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BIRZEIT

UNIVERSITY

ELECTRICAL

ENGINEERING

DEPARTMENT

ANALOG AND DIGITAL

COMMUNICATION LAB

(ENEE 411)

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2

Table of Contents

Experiment 1 AM Modulation and Detection ... 4

Experiment 2 DSB-SC and SSB ... 11

Experiment 3 FM Modulation and Demodulation ... 19

Experiment 4 FDM ... 26

Experiment 5 ADC ... 34

Experiment 6 DAC ... 42

Experiment 7 PCM ... 52

Experiment 8 TDM ... 57

Experiment 9 ASK (Amplitude Shift Keying) ... 63

Experiment 10 FSK (Frequency Shift Keying) ... 70

Experiment 11 BPSK(Binary Phase Shift Keying) ... 75

Experiment 12 QPSK(Quadri- Phase Shift Keying) ... 80

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3 EXPERIMENT.1

AM Modulation and Demodulation

Objectives:

 To understand the theory of amplitude modulation and demodulation.

 To design and implement the two types of AM modulator: transistor and balanced modulator.

 To design and implement the two types of AM demodulator: the diode detection and the product detection.

 To understand the measurements and adjustments of AM modulator and demodulator.

PrelaB Work:

Use MATLAB command and M files to draw the demodulated signal after the envelope detector given that: ) cos( )] cos( 1 [ ) (t A t t SAMc  mc

1. Write the mathematical expression for the demodulated signal.

2. Use MATLAB command and M files to draw the demodulated signal for the following three cases:

a. Ac=16v, modulation index=0.22, modulating signal frequency=800Hz b. Ac=16v, modulation index=1, modulating signal frequency=800Hz c. Ac=16v, modulation index=1.85, modulating signal frequency=800Hz

3. Discuss your result in each part .you must write the commands which are used in the Pre-lab.

Equipment Required:

 2 AC Function Generators  DC Power Supply

 ETEK ACS-3000-02 Module  Connection wires

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4

Theory:

Modulation

: the process by which some characteristic (like: amplitude, frequency or phase) of a carrier signal is varied in accordance with the modulating signal (message signal).The signal modulation is used in order to transmit messages over long distances and also to transmit signals from various sources simultaneously over a common channel.

Amplitude Modulation (AM): The process in which the amplitude of the carrier varies linearly

with message signal.

The general formula for the modulated AM signal:

From the above formula we find that in order to generate an AM signal we just need to add a DC signal with the message signal then multiply the added signal with the carrier signal.

The analog multiplier is the basic modulator that is used to generate AM signal as shown in fig1.1:

Fig(1.1): Analog Multiplier.

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Frequency

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Frequency

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message

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M odulation

:

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cos(

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c m m c m m c m c AM

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5

The Modulation Index µ:

There is an important parameter in the AM modulation which is called the modulation index (µ) which is equal to Am/Ac .

The Frequency Spectrum for the AM modulated signal:

Equation (1-1) can be written as :

( )

[ ( ( ) ) ( ( ) )] ( ) ( )

The first term of equation (1-2) represents the double side band signals .While the second term represents the carrier signal. Since the audio signal is hidden in the double side bands and the carrier signal does have no data, the AM modulation is lower efficiency than double side band suppressed carrier (DSB-SC) modulation but its demodulation circuit is much simpler.

If the double side bands get stronger then the transmission efficiency is getting better. From equation (1-2) we find that the double side bands are proportional to µ so larger µ is getting better efficiency.

The transmission power efficiency η:

( )

The modulation index is smaller or equal to .So if µ <1 an over modulation will happen for the AM signal , which means that the variation of the carrier is no longer sinusoidal and the signal is distorted . So it is unable to recover the signal at the receiver using the envelope detector (as we will see later).

AM modulator practical circuits:

As we said previously we can implement the AM modulators by using a multiplier. In electronics circuits a multiplier is implemented by the nonlinear characteristics of active elements. There are many circuits’ works as a multiplier but in this experiment we will deal with two types:

1- Transistor AM modulator 2- Balanced Modulator (MC1496)

Demodulation

: is the process of restoring the message signal at the receiver side. In this

experiment we will show two types of AM demodulators: 1- Envelope detector (asynchronous detector) 2- Product detector (synchronous detector)

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6

Detection Using Envelope detector:

Fig(1-2) shows the envelope detector operation. After the diode rectifies the AM signal (removing the negative part) then the RC low pass filter obtains the AM envelope which is the message signal. The envelope detector is able to recover the message signal if the following conditions are achieved:

1- fc<<10 fm 2- µ=[0,1]

3- Tc>>RC>>Tm .Where Tc=1/fc, Tm=1/fm, RC is the time constant of the RC low pass filter .

Fig(1.2): Envelope detector.

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7

Detection Using Product detector:

Fig(1.3): Product detector.

The output of the product as shown in fig (1-3): ( )

( ) [ ( )] ( ) ( )

The first term of eq(1-4) is a DC signal while the second is the message signal , the third term is the second harmonic of the AM signal which is rejected by the low pass filer.

The two types of the detectors have its own advantages and disadvantages. For the envelope detector which is asynchronous detector, its circuit is simple but its performance is not better as the product detector .However, the product detector’s circuit is more complicated and requires synchronous for both carrier signal and AM signal (same phase and same frequency), otherwise the quality of the output will be affected.

Procedure:

Transistor AM modulator:

1- Refer to ACS3-1 on ETEK kit ACS-3000-02 module.

2- At the audio input port (Audio I/P) ,use the function generator to input a sine wave 600mV amplitude and 1KHz frequency. At the carrier signal port (Carrier I/P) ,input a sine wave 1.7 amplitude and 500 KHz frequency.

3- By using the oscilloscope, observe the AM modulated signal at the modulator output port (AM O/P).Adjust VR1 so that the AM signal is maximum without distortion (VR1 is used to change the operation point of the transistor and it also controls the magnitude of the carrier) .

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8 5- Try to change the frequency and the amplitude of the message signal. record your

results.

Balanced AM modulator:

1- Refer to ACS3-2 on ETEK kit ACS-3000-02 module.

2- Let J1 short,J2 open so that R10=6.8KΩ (R10 determines the magnitude of the bias current for the modulator).

3- At the audio input port (Audio I/P) ,use the function generator to input a sine wave 500mV amplitude and 1KHz frequency. At the carrier signal port (Carrier I/P) ,input a sine wave 2V amplitude and 500 KHz frequency.

4- By using the oscilloscope, observe the AM modulated signal at the modulator output port (AM O/P).Adjust VR2 so that the AM signal is maximum without distortion (VR2 controls the gain of the modulator) . Adjust VR1 so that the value of µ is less

than 1 (VR1 controls the value of µ). Record your results.

5- Change the value of VR1 until µ=1 (100% modulation). Let µ<1 (over modulation) observe the AM signal. Record your results.

6- Try to change the amplitude of the message signal and its frequency. notice the effects on the AM signal. (Keep the connection as it is for the second part ).

Diode Detector:

1- At the audio input port (Audio I/P), use the function generator to input a sine wave 350mV amplitude and 3KHz frequency. At the carrier signal port (Carrier I/P) ,input a sine wave 2V amplitude and 500 KHz frequency.

2- Adjust VR1 so that µ is maximum and VR2 so that AM O/P1 approximate between 150-350mVp-p.

3- Connect AM O/P1 to the input AM I/P of the diode detector (ACS 4-1 on ETEK ACS-3000-02 module).

4- Observe the signal at TP1,TP2,TP3 and TP4.

5- Change the value of VR1 so that µ is less than 1.record your results.

6- Change the message signal amplitude and frequency and notice their effects on the signal at the detector output.

Product Detector:

1- Keep the connection for the balanced modulator the same as in the previous part. 2- At the audio input port (Audio I/P), use the function generator to input a sine wave

350mV amplitude and 3KHz frequency. At the carrier signal port (Carrier I/P) ,input a sine wave 2V amplitude and 500 KHz frequency.

3- Adjust VR1 so that µ is less than 1.

4- Connect AM O/P1 to the input AM I/P of the product (Coherent) detector (ACS 4-2 on ETEK ACS-3000-02 module).

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9 5- Connect the carrier signal input of the product detector (Carrier I/P) with the same

carrier signal in AM modulator (for synchronization).

6- Adjust the value of VR1 (controls the amplitude of the carrier),VR2(controls the amplitude of the message signal) and VR3(controls the gain of the detector) so that the signal at the output of the detector is maximum without distortion.

7- Try to change the frequency of the message signal and the frequency of the carrier. Observe the signal at the detector output.

Questions:

1. Calculate the power efficiency for different modulation index µ=0.25, µ =0.5, µ =0.75, µ =1

2. An AM detector gets a wave with the following mathematical expression: V(t) = 5(1 + 0.5sin(2l000t)sin(2455000t)

 Explain what is this wave and the meaning of the parameters: 5,0.5, 1000, 455000

 What is the modulation coefficient of the above wave and what is the relation between the modulated wave amplitude and the' carrier wave amplitude?

 What is the bandwidth of this AM modulated wave?

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10 EXPERIMENT.2:

DSB-SC and SSB

Objectives:

 To understand the theory of DSB-SC and SSB modulation and demodulation.  To design and implement the DSB-SC and SSB modulators and demodulators.  To understand the waveforms and frequency spectrums of DSB-SC and SSB signals.  To understand the measurements and adjustments of DSB-SC and SSB modulators and

demodulators.

PreLab work:

Using Matlab software and Simulink, to show graphically the time domain of SSB-SC modulated Signal. Taking the modulating signal m(t)cos2(1500)t and the carrier signal

t t c( )4cos2(100000) .

Equipment Required:

 2 AC Function Generators  DC Power Supply

 ETEK ACS-3000-03 Module  Connection wires.

Theory:

DSB-SC and SSB modulation:

Recall that the AM modulated signal is given by:

( )

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11

Fig(2-1): Frequency spectrum of AM.

Since the message signal is hidden in the double side bands and the carrier does not contain any signal, therefore, the power is consumed in the carrier during the transmission of AM signal. This will explain that the AM modulation has a low transmission efficiency (it could be only 33% in the best case). So the idea from Double Side Band Suppressed Carrier modulation (DSB-SC) is to suppress the carrier or in other words, to make the carrier amplitude equals to zero. This technique will improve the power efficiency.

We can use DSB-SC to obtain SSB modulation. It is not necessary to transmit both side-bands. Either one can be suppressed at the transmitter without any loss of information. The information represented by the modulating signal is contained in both the upper and the lower sidebands. In SSB modulation we eliminate the carrier and one sideband, a power savings of over 83 percent is realized. Additionally, the bandwidth required for SSB is theoretically one-half that required when both sidebands are transmitted.

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12

Fig(2-3):Frequency spectrum of SSB ( Lower sideband).

Fig(2-4):Frequency spectrum of SSB ( Upper sideband).

Fig(2-5):block diagram of DSB-SC modulation.

We can also use the DSB-SC modulation to obtain SSB modulation. We utilize two DSB-SC modulators and let the phase difference between the two audio signals and the two carriers to become 90 degree, i.e: (DSB-SC)Q- quadrature component and (DSB-SC)I-in phase component where:

(DSB-SC)I = cos2π(fc-fm)t+ cos2π(fc+fm)t ………. (2-2) (DSB-SC)Q = cos2π(fc-fm)t - cos2π(fc+fm)t ………. (2-3)

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13 Equations (2-2) and (2-3) show that both (DSB-SC)I and (DSB-SC)Q connect to an adder to obtain USSB or LSSB at the output port.

LSSB= (DSB-SC)I+ (DSB-SC)Q= cos2π(fc-fm)t ………. (2- 4) USSB= (DSB-SC)I- (DSB-SC)Q= cos2π(fc + fm)t ……….(2- 5)

During transmission, the power consumption of SSB modulation is less than DSB-SC modulation so the sequence of power consumption for these different types of modulation is as follows: AM <DSB-SC < SSB.

Implementation of DSB-SC modulator:

DSB-SC modulation is a kind of AM modulation so we can use the structure of AM modulator to implement DSB-SC. In this experiment we will utilize balanced modulator MC1496 to design DSB-SC modulated signal.

Fig(2-6):Circuit diagram of DSB-SC modulation by utilizing MC1496.

Implementation of SSB modulator:

From equations (2-4) and (2-5), we know that the SSB modulator is the combination of two DSB-SC modulators. Figure (2-6) is the block diagram of SSB modulator.

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14

Fig(2-7):Circuit diagram of SSB modulator.

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15

Fig(2-9):Circuit diagram of linear adder.

DSB-SC and SSB demodulation:

As we know:

( ) ( ) ( )………..….(2- 6)

Multiply equation (2-6) by 2cos(2πfct):

( ) ( ) ( ) ( )

( )[ ( ) ] ( ) By using Fourier Transform on equation (2-7) we get:

( ) ( ) [ ( ) ( )] ( )

When ( ) passes through a low pass filter which its bandwidth equals or larger than the bandwidth of the message signal but smaller than 2fc then the only term left in equation (2-8) is 0.5M(f). The block diagram for the DSB-SC demodulator is shown in the figure below:

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16 From equations 4) and 5) we conclude that we can use the demodulator above figure (2-10)as a SSB demodulator.

Implementation of DSB-SC and SSB demodulator:

DSB-SC and SSB demodulator which is called a coherent product detector will be implemented in this circuit using MC1496 as shown in the diagram.

Fig(2-11):Circuit diagram of the coherent product detector.

Procedure:

Part 1: DSB-SC and SSB modulators:

1- Refer to module ACS5-1 on ETEK ACS-3000-03 Kit.

2- At the audio input port (Audio I/P) put a sine wave with 400mV amplitude and 1KHz frequency. Then at the carrier input port (Carrier I/P) put a sine wave with also 400 mV amplitude and 200KHz frequency.

3- By using oscilloscope, observe the signals at the audio output ports TP1 and TP2 at the same time. Adjust the variable resistor “QPS” so that the phase shift between TP1 and TP2 is 90º.

4- By using oscilloscope, observe the signals at the carrier output ports TP3 and TP4 at the same time. Adjust the variable resistor “Phase Adjust” so that the phase shift between TP3 and TP4 is 90º.

5- By using oscilloscope, observe TP5 (DSB-SC(Q)) then adjust VR1(gain adjustment) so that the output amplitude is maximum without distortion. Also, adjust VR3 (modulation index µ) so that µ=1.Record your result.

6- By using oscilloscope, observe TP6 (DSB-SC(I)) then adjust VR2(gain adjustment) so that the output amplitude is maximum without distortion. Also, adjust VR4 (modulation index µ) so that µ=1.Record your result.

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17 7- Try to change the amplitude of the message signal then its frequency and observe the

effects.

8- Try to change the amplitude of the carrier signal then its frequency. Record your results.

9- Keep all connections as they are.

Part 2: DSB-SC demodulator:

1- To implement the product detector of DSB-SC refer to ACS6-1 on ETEK ACS-3000-03 module. Let J1 be short circuit and J2 open circuit.

2- Connect the modulated DSB-SC(I) signal in module ACS5-1 to the input terminal (DSB-SC/SSB I/P) of the product detector in module ACS6-1.At the same time, input the same carrier signal in ACS5-1 to the carrier signal input port (Carrier I/P) in ACS6-1.

3- By using Oscilloscope, observe the output signal of the product detector (Audio O/P) in ACS6-1.

4- Adjust VR1 and VR2 so that the amplitude at (Audio O/P) is maximum without distortion then record the waves of the product detector at TP1 and TP2 .

5- Let J1 is open and J2 is short and repeat the steps above. 6- Keep only the connections at the modulator side.

Part 3: SSB demodulator:

1- Connect the modulated SSB signal (SSB O/P) in module ACS5-1 to the input terminal (DSB-SC/SSB I/P) of the product detector in module ACS6-1.At the same time, input the same carrier signal in ACS5-1 to the carrier signal input port (Carrier I/P) in ACS6-1.

2- By using Oscilloscope, observe the output signal of the product detector (Audio O/P) in ACS6-1.

3- Adjust VR1 and VR2 so that the amplitude at (Audio O/P) is maximum without distortion then record the waves of the product detector at TP1 , TP2 and (Audio O/P) .

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18 EXPERIMENT.3

FM Modulation and Demodulation

Objectives:

 Creating a modulated FM wave using MC4046 and LM566 Modulators.

 Investigating the influence of changing the frequency of the signal at the modulator voltage output.

 Calculation of the frequency deviation and the bandwidth.

 Modulation and detection of the FM signal using MC4046 and LM565 detectors.  Calculation of the modulation coefficient.

Equipment Required:

ETEK ACS-3000-04(MC4046 and LM566 Modules)  Power supply

 Oscilloscope

 Audio signal generator  Banana wires

PreLab work:

Consider the frequency modulated signal:

)] 2 sin( 4 ) 17 ( 2 cos[ ) (t t t S    

a. Find the message signal m(t). b. Plot s(t) versus t for -1 ≤ t ≤ 1.

c. Differentiate s(t) with respect to t and plot ds(t)/dt for -1 ≤ t ≤ 1. Notice how this operation transforms an FM waveform into an AM waveform.

d. Apply ds(t)/dt to an ideal envelope detector, subtract the dc term and show that the detector’s output is linearly proportional to m(t).

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19

Theory:

Frequency Modulation: the process by which frequency of the carrier must be varied with

respect to the message signal.

FM modulation (Direct Method):

In practice, FM modulation is implemented by controlling the instantaneous frequency of a voltage-controlled oscillator (VCO). The amplitude of the input signal voltage controls the oscillation frequency of the VCO output signal.

The instantaneous frequency given by:

) ( )

(t fc Kfm t

fi   ……….... (3.1)

Where Kf: is the proportionality constant with unit (HZ/volt) A typical characteristics of VCO looks like these:

Fig(3-1):A typical characteristics of VCO.

The General Formula of FM Modulated Wave

       

  t c FM t A fct Kf m d S ( ) cos 2 2 ()  ……….... (3.2)

When message signal m(t) Amcos(2fmt)

What is the formula of FM modulated wave? The modulation coefficient

fm KfA fm fm    ……… (3.3)

Wheref : is the peak frequency deviation. Fm: message signal frequency

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20

Band width of FM Modulated signal:

The band width of fm modulated signal given by Carson’s rule as the following:

BWFM 2(ffm)... (3.4) BWFM 2fm(1)………..….... (3.5)

Advantages of FM Modulation :

1. Constant power

2. Better noise immunity [good quality]

3. Power efficiency: the total transmitted power is constant and is independent of the message signal.

FM DeModulation :

FM signals can be demodulated using different techniques. Our focus in this experiment will be on the Slope Method, which uses a cascaded differentiator with an envelope detector circuit as illustrated in Fig (3.2). The differentiator basically produces an AM-like signal that is then demodulated by the envelope detector block.

Fig (3.2): FM modulator and demodulator.

        cos (2 2

( ) ) ) ( 0    f t k m d A t s t f c c ……….. (3.6) Where: ) (t m = modulating signal f = carrier frequency c A = carrier amplitude c

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21 kf = sensitivity factor

If we let the modulating signal be a pure sinusoidm(t) Amcos2fmt, then equation (1.1) becomes

f t f t

A t f f A k t f A t s m c c m m m f c

ccos (2 sin2 cos(2 sin2 ) (          ……… (3.7)

Where kfAm f = frequency deviation

= m

f f

= Modulation index (Deviation ration)

There are two types of FM signals depending on the value of ; NBFM ( 1) and WBFM (all).

Differentiating s(t) in (3.7)with respect to t we get:

                  2 2 ( ) sin (2 2

( ) ) ) ( 0      f k m t A f t k m d dt t ds t f c c f c ……….…. (3.8)

Note that equation (3.8) similar to AM modulated signal. The output after the envelope detector given as the following:

2 f 2 k m(t)

Acc   f ………... (3.9)

You must add capacitor to do dc blocking. What is the output after the capacitor?

Procedure:

Part One: Modulation and Demodulation using MC4046 and PLLMC4046Modules fig

(3.3) and fig (3.4):

1. Connect the oscilloscope to (FM O/P) output in CD4046 module and observe the output signal .adjust the variable resistor VR1 so that the output signal 20 KHz square wave. 2. Connect the signal generator to Audio signal input (Audio I/P) and set the amplitude of

the generator 10vp-p and 1 KHz frequency of the sine wave.

3. Connect the oscilloscope to the output of the modulator (FM O/P) and observe the output signal and take at least three measurements of frequency variations.

4. Repeat step 2 and step 3 for triangular input signal and square input signal and draw the Modulated signal in each case.

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22 5. Adjust the free running frequency (fo) of the VCO output port TP1 to 20KHz in

PLLCD4046 Module.

6. Connect the output port (FM/OP) of the VCO MC4046 to the input port (FM I/P) of the PLLMC4046.

7. At the Audio input port (Audio I/P) of the VCO connect the function generator choose sine wave with frequency 1 KHz and choose a suitable value of amplitude to recover the output.

Fig.(3.3): FM Modulation and demodulation using MC4046 module.

Fig (3.4): FM Modulation and demodulation using PLL MC4046 module.

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23 1. Set J1 and J3 short circuit and J2 open circuit the selected capacitor C4=10nf in the FM

modulator LM566 Module

2. Connect the oscilloscope to (FM O/P) port adjust the variable resistor VR1 so that the frequency of the (FM O/P) output equal to 20 KHz

3. Connect the signal generator to Audio signal input port (Audio I/P) and select sinusoidal signal with amplitude 10vp-p and frequency 1 KHz.

4. Connect the oscilloscope to the output of the FM modulator (FM O/P) port then measure at least three variations in frequency and draw the FM modulated signal.

5. Repeat step 3 and step 4 for triangular and square signal and calculate the maximum frequency deviation, the modulation coefficient, the desired bandwidth for the square modulating signal.

Fig (3.5): FM modulator and demodulator using LM566 module.

Part Three: Modulation and Demodulation using PLL LM565 Module:

1. Set J3 short circuit and J1 and J2 open circuit to choose C5=10nf in LM565 module. 2. Connect the oscilloscope to (VCO O/P) port adjust the variable resistor VR1 so that the

free running frequency fo equal to 20 KHz.

3. Connect the output port of (FM O/P) of the VCO LM566 module to the input port (FM I/P) of the PLL LM565.

4. At the Audio input port (Audio I/P) Connect the function generator and select sinusoidal signal with maximum amplitude and 1 KHz frequency.

5. Connect the oscilloscope to the output of the FM detector (Audio O/P) and draw the output.

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24 1. Set J2 short circuit and J3 and J1 open circuit C2=100nf

2. Adjust the variable VR1 so that the free running frequency fo of the (VCO O/P) equal 2 KHz.

3. Set J1 open circuit this means that SW1 is open

4. At the demodulated FM input port (FM I/P) connect the signal generator and choose square wave with 5vp-p and 2 KHz frequency. Then change the input frequency as shown in the table (2-1) and measure the amplitude of (Audio O/P) at each frequency. 5. Draw the frequency vs the voltage output (Characteristic of the VCO).

Frequency 0.5KHz 1KHz 1.5KHz 2KHz 2.5KHz 3KHz 3.5KHz 4KHz 0.5KHz Amplitude

Table (3-1)

Fig (3.6): Voltage and frequency conversion using LM565 module.

6. Set J3 short circuit and J1 and J2 open circuit C5=10nf

7. Adjust the variable VR1 so that the free running frequency fo of the (VCO O/P) equal 20 KHz.

8. Set J1 open circuit this means that SW1 is open

9. At the demodulated FM input port (FM I/P) connect the signal generator and choose square wave with 5vp-p and 20 KHz frequency. Then change the input frequency as shown in the table (2-2) and measure the amplitude of (Audio O/P) at each frequency.

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25 10. Draw the frequency Vs the voltage output (Characteristic of the VCO).

Frequency 8KHz 12KHz 14KHz 15KHz 18KHz 22KHz 23KHz 24KHz 25KHz Amplitude

Table (3-2)

Questions:

Question#1:

1) What are the significant frequencies and the power in each harmonies of a FM modulated wave

for:

β=0.5(refer to Bessel function table) and for:

β=2(refer to Bessel function table) When the carrier wave is:

Vc(t) =8 cos(2π50000t)

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26

Bessel function table

Hint to solve the question:

a. Jn (β) are Bessel functions of the first kind of order n and argument β. β appears in Brackets because the Bessel functions are dependent on β.

b. Carrier wave in fc frequency and Vc . J0 (β) power.

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27 EXPERIMENT.4

FDM Multiplexer and Demultiplexer

Objectives:

 To understand the operation theory of frequency Division Multiplexing FDM and Demultiplexing.

 To design and implement the FDM multiplexer and Demultiplexer.

Equipment Required:

ACS11-1 and ACS12-1 of ETEK ACS-3000-06 module.

DC Power Supply.

Connection wires.

Theory:

If the transmission channel consists only of one modulated signal, then the usage of the channel is very low and the efficiency is also not good. Therefore, in order to comfort with the economic benefit, the channel must be able to transmit multiple signals, such as in the telephone system. As you know the frequency range of the sound is 300Hz to 3 KHz so in order to transmit this kind of signal via a single channel, we must divide the signal into several slots to prevent the interference then we can obtain the signal at the receiver. There are two types of signal division Time Division Multiplexing (TDM) and Frequency Division Multiplexing (FDM).

FDM Multiplexing:

Figure (4.1) is the system block diagram of FDM. Like TDM, FDM is used to transmit multiple signals over the same communication channel simultaneously. However, unlike TDM, FDM does not use pulse modulation. Figure (4.1) assumes that all the input audio signals are low pass pattern and after each input signal, there will be a low pass filter to remove all the unwanted signals except the audio signals. Then the audio signals will be sent into the modulator so that the frequency range of the signals will shift to different region. The conversion of the frequency is controlled by the carrier signal. Therefore, we utilize the simplest technique which is the AM modulation to implement the modulator. Then the modulated signal will pass through a band pass filter which can limit the signal bandwidth to prevent the interference between each signal. Finally, the signals will be added by a linear adder. As compare to TDM, we utilize AM modulation to implement FDM system and sampling to implement TDM system.

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28

Fig.(4.1):Block diagram of FDM Multiplexer.

In this experiment, we build each balanced modulator by utilizing MC1496 and use different carriers for each modulator. As you know, the output from each balanced modulator is a DSB-SC signal. Then, the DSB-DSB-SC signals will be added by a linear adder in order to produce the FDM signal.

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29

Fig.(4.3):Circuit diagram of the linear adder.

FDM Demultiplexing:

There are two ways to implement FDM demultiplexer. The first way is shown in figure (4.4). Let the FDM signals pass through a band pass filter, this filter will remove the signal which its frequency is larger and lower than f0 and only left a single DSB-SC modulated signal. After that, this signal will pass through the LPF which recover the modulated signal and obtain the original audio signal. While Figure (4.5) shows the second way to implement the FDM demultiplexer which is called synchronous product detection. After the signal passes through the synchronous product detector, we will add a LPF to remove all the unwanted signals and recover the original audio signal.

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30

Fig.(4.5):Block diagram of synchronous product detector.

Fig.(4.6):Circuit diagram of synchronous product detector.

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Procedure:

FDM Multiplexing:

1- Refer to the audio signal generator in ACS11-1 of ETEK ACS-3000-06 module.

2- Using the oscilloscope to observe the audio signal from the signal generator 1 output (TP1) .Adjust the variable resistors “Audio Frequency Adjust1” and “Audio Gain Adjust1” to obtain an output audio signal with 500 Hz frequency and 620mV amplitude.

3- Using the oscilloscope to observe the audio signal from the signal generator 2 output (TP3) .Adjust the variable resistors “Audio Frequency Adjust2” and “Audio Gain Adjust2” to obtain an output audio signal with 800 Hz frequency and 620mV amplitude.

4- Using the oscilloscope to observe the audio signal from the signal generator 3 output (TP7) .Adjust the variable resistors “Audio Frequency Adjust3” and “Audio Gain Adjust3” to obtain an output audio signal with 1.2 kHz frequency and 620mV amplitude.

5- Refer to the carrier signal generator in ACS11-1 of ETEK ACS-3000-06 module.

6- Using the oscilloscope to observe the carrier signal from the carrier signal generator 1 output (TP2) .Adjust the variable resistor “Carrier Gain Adjust1” so that the output amplitude of the carrier is 620mV.

7- Using the oscilloscope to observe the carrier signal from the carrier signal generator 2 output (TP4) .Adjust the variable resistor “Carrier Gain Adjust2” so that the output amplitude of the carrier is 620mV.

8- Using the oscilloscope to observe the carrier signal from the carrier signal generator 3 output (TP8) .Adjust the variable resistor “Carrier Gain Adjust3” so that the output amplitude of the carrier is 620mV.

9- Using the oscilloscope to observe output signal of the balanced modulator 1(TP5) .Adjust the variable resistor “Modulator Adjust 1” so that the output is DSB-SC modulated signal.

10- Using the oscilloscope to observe output signal of the balanced modulator 2(TP6). Adjust the variable resistor “Modulator Adjust 2” so that the output is DSB-SC modulated signal.

11- Using the oscilloscope to observe output signal of the balanced modulator 3(TP9). Adjust the variable resistor “Modulator Adjust 3” so that the output is DSB-SC modulated signal.

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32 12- Using the oscilloscope to observe output signal waveform of FDM output port (FDM

O/P).

FDM Demultiplexing:

1- To implement a product detector (shown in fig.(4.5)) and the low pass filter (shown in fig.(4.6)), refer to figure ACS12-1 on ETEK ACS-3000-06 module.

2- Connect (FDM O/P) in ACS11-1 to (FDM I/P) in ACS12-1.

3- Connect the carrier signal (TP2) in ACS11-1 to (Carrier I/P1) in ACS12-1, (TP4) to (Carrier I/P2) and (TP8) to (Carrier I/P3).

4- Using oscilloscope to observe the output signal waveforms of (Audio O/P1), (Audio O/P2) and (Audio O/P3), then adjust the variable resistors “Carrier Adjust 1”, “Gain Adjust 1”, “Carrier Adjust 2”, “Gain Adjust 2”, “Carrier Adjust 3” and “Gain Adjust 3” so that the output waveforms are maximum without distortion. Record your results.

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33 EXPERIMENT.5

Analog to Digital Conversion (ADC)

Objectives:

 To understand the operation theory of analog to digital converter.

 To implement the analog to digital converter by using ADC0804 and ADC0809.

Equipment Required:

 ETEK-DCS-3000-07 module  Signal Generator  Oscilloscope  DC-Power supply

Theory:

Figure 5-1 is the characteristic curve of an ideal 3-bit analog to digital converter, and the analog input range is from 0 V to 5 V. We can divide the input signal into 8 (2^3 = 8) ranges, at each range all the analog values use the same binary code to represent, and this binary code is corresponding with the mid-value. Therefore, during the processing of converter, it consists of ± 1/2 least significant bit (LSB) quantization uncertainty or quantization error, and also includes the previous converter that has the analog error, then all of the errors comprise the error value of ADC. One of the methods to reduce the quantization error is to increase the number of bits of the converter. The more the numbers of bits, the more the numbers of ranges and the data signal will be more detail. This is because the ± 1/2 LSB becomes small, therefore, the quantization error will reduce. Quantization value (Q) means when the digital output changes LSB, the required input voltage value also changes The methods of conversion for analog to digital converter are various, sample-and-hold, S&H circuit will capture the input signal Vin to avoid normally can be divided as AID conversion methods are digital-ramp ADC, successive approximation ADC, flash ADC and tracking ADC. In this chapter, only the successive approximation ADC is discussed, therefore, we will discuss on the operation theory of successive approximation ADC.

Figure 5-2 is the block diagram of successive approximation ADC, which is provided with 8-bit resolution. When we input the analog signal, sample-and-hold, S&H circuit will capture the input signal Yin to avoid any signal change during con version period. At this moment , the control

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34 logic will store all the bit s and reset to" 0 ", follow by the most significant bit, MSB D7 is set to " 1 ". Thus, the output voltage of DAC is:

Fig(5-1)

Fig(5-2)

This voltage is half of the reference voltage Vref, If the input voltage Vin is higher than V( D), then D0 to D7 remains at " 1 ", otherwise alters to " 0 ". Next, make second bit D6 as " 1 ", after

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35 passing through a DAC then obtain an output voltage V(D), at this moment comparing the new V(D) and Vin, if Yin is higher than V(D), then D6 remains at " 1 " otherwise alters to " 0 ". Similarly for the others until the comparison of D0 to D7 have been completed, then we can obtain the complete D7 to D0 digital output.

ADC0804 Analog to Digital Converter

ADC0804 is a 20-pin DIP package with an 8-bit resolution single channel IC. The analog input voltage range is from 0 V to 5 V with single 5 V power supply, 15 mW power consumption and 100 us conversion time . As a result of this IC contains of 8-bit resolution, so it has 2^8=256 quantization steps, if the reference voltage is 5 V , each step will be 5/256 = 0.01953 V . 00000000 (OOH) represents 0.00 V and 1111111 (FFH) represents 4.9805 V. The unadjusted error of ADC0804 is ±1 LSB, which is 0.01953 V, which includes full-scale error, offset error and non-linearity error. Figure 5-3 shows the pins diagram of ADC0804. In figure 5-3, the D0 to D 7 of ADC0804 is the 8-bit output pins , when CS and RD are low, the digital data will be sent to the output pins. If any pins of CS and RD are high, then D0 to D7 are in floating condition. WR is the write control signal, when CS and WR are Low, ADC0804 will do the clear action, when WR backs to high, ADC will start the conversion. CLK IN (Pin 4) is the clock input , the frequency range starts from 100 kHz to 800 kHz. During the conversion period, INTR is at high level and then after the conversion completed, INTR will alter to low. Pin6 Vin (+) and pin7 Vin (-) are differential analog signal inputs, ordinarily used single input terminal and Vin ( - ) is connected to ground. ADC0804 has two ground terminals, one is analog ground (A GND) and another one is digital ground (D GND). Pin 9 (Vref /2) is 1/2 of the reference voltage, if pin 9 is floating , then the 1/2 reference voltage equals to power supply voltage Vee. ADC0804 has a built-in Schmitt trigger as shown in figure 5-4. If we add a resistor and capacitor at CLK R (pin 19) and CLK IN (pin 4), then we can generate the ADC operating time.

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36 Therefore, we need not input an external clock signal to CLK IN terminal . We can determine the clock signal by the external R and C via pin 4 and pin 19.

Figure 5-5 is the circuit diagram of ADC0804 analog to digital converter, the analog signal input range is controlled by VR2 and input through the Vin ( +) terminal and at the same time, the Vin ( -) is short circuit. Vref / 2 is provided by R1 , R2 and VR1. C1 and R3 is used to control the clock of the circuit, CS and RD are short circuit, so that the IC is enable, then let WR and INTR connect to SW1 in order to simulate the control signal.

Fig(5-4)

Procedure:

ADC0804 analog to digital converter

1. Refer to the circuit diagram in figure 5-4 on ETEK ACS-3000-07 module. Set J1 be open circuit.

2. Use the digital voltage meter to measure the reference voltage input port (TP1). Adjust VR1 so that the voltage of TP1 is 2.5 V. At this moment, ADC0804 analog voltage input range is 0 V to 5 V.

3. By using oscilloscope, observe on the TP2.

4. Adjust VR2 so that the input voltage of the analog signal input port (TP3) is 0 V, and record the measured results in table 5-1.

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37 5. Set J1 be short circuit to maintain the output digital signal. Observe on the changes of

LED, LED "on" represents " I", LED "off' represents "0".

ADC0809 analog to digital converter

1. Refer to the circuit diagram in figure 5- 5 on ETEK ACS-3000-07 module.

2. At the CLK input port (CLK I/P), input 120 kHz frequency and a TTL signal with 5 V offset.

3. Let SW3, SW2 and SW1 switch to GND (push down the slide switch), at this moment, the multiplexer selects to channel 0 and the analog signal is inputted from the IN0 input.

4. Use the digital voltage meter to measure the TP1 of channel 0. Adjust VR1 so that the input voltage of TP1 is similar to the values in table 5-2. Observe on the changes of LED, LED "on" represents “1’’. LED "off' represents "0", then record the measured result s in table 5-2.

5. Use the digital voltage meter to measure the TP2 of channel 1 until TP7 of channel 6, and then record the measured results in table 5-3.

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38

Table(5-1)

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39

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40 EXPERIMENT.6

Digital to Analog Conversion (DAC)

Objectives:

 To understand the operation theory of digital to Analog converter.

 To implement the digital to analogue converter by using ADC0804 and ADC0809.

Equipment Required:

 ETEK-DCS-3000-07 module  Signal Generator  Oscilloscope  DC-Power supply

Theory:

Digital to analog converter (DAC) is a device, which converts the digital signal to analog signal. We normally store a digital signal in a media or transmission line. Then a DAC changes the digital signal to an analog signal in order to control data display or further analog signal processing. For example, from a digital communication system, when a receiver receives the digital modulation signal , then after via a demodulator and decoder, we can obtain the digital signal, and follow by using DAC to convert this digital signal to the analog signal. Next we will discuss the basic operation theory of DAC.

Basically, DAC is a digital code that represents digital value converted to analog voltage or current. Figure 6-1(a) is a genera 14-bit DAC binary codes , the digit al input terminal [D3 D2 D1 D0] are manipulated by the register in a digital system . The 4-bit code represent s 2^4= 16 groups of 2 . binary state value, as shown in figure 6-1(b). For every binary code input, DAC will output a voltage (Vout),

which is double or other order of the binary value. According to this, analog output voltage Vout and the

digital input binary values are the equivalent. If the DAC output is current, l out, the theory is similarly.

Figure 6-2 is the basic block diagram of DAC. The reference voltage (Vref) is used to provide the reference voltage during conversion, Then due to the magnitude of the input binary code , the digital control switch will output different binary codes to the resistors network. Normally, the DAC analog output is represented by current, if we want to obtain the voltage output, we need to connect an operational amplifier, which can convert the current to voltage level.

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41

Fig(6-1a)

Fig(6-1b)

Fig(6-2)

Resolution and Step Size:

The resolution of DAC illustrates that when the digital input terminal changes a unit, it will produce a small change at the analog output terminal, which is normally the LSB levels. Refer to

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42 figure 6-1(b), when the digital input value changes a unit Vout will change at least 1 V, so the resolution is 1V.

Resolution is also called step size because Vout will change, when the digital input step varies from one to another. Figure 6-3 shows a 4-bit binary counter as DAC digital input signal, the counter has a clock input, so it can output 16 types of statuses continuously in cycle . The output waveform of DAC is every step with 1V change. When the counter generates 1111, the DAC output is the maximum value, which is 15 V. We call this situation as full-scale output. When the counter generates 0000, the DAC output is 0 v. Resolution or step size is to indicate the difference between two steps. For example, if the step size is 1 V then the difference between the steps is 1V.

Figure 6-3 shows 16 types digital inputs corresponding to the 16 levels of output steps waveform. From 0 V to 15 V (full-scale) , there are only 15 steps size. Generally, N bits of DAC will produce 2N different levels and 2N-1 steps size.

Fig(6-3)

DAC 0800 Digital to Analog Converter:

DAC 0800 is a cheap and commonly used 8-bit DAC, the internal circuit consists of reference voltage power supply, R-2R ladder resistors network and transistor switch. The voltage power supply range is between ± 4.5 V to ± 18 V, under the ± 5 V condition, the power loss is approximately 33mWand the settling time is approximately 85 ns. Figure 6-4 is the pins diagram

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43 of DAC0800. Figure 6-5 is the circuit diagram of DAC0800 single polarity voltage output, which D7 ~ Do are the 8-bit digital input s. The positive reference voltage is + 5V and passes through R1 to connect to Vref(+) (pin14). The negative reference voltage is GND and passes through R2 to connect to Vref (-) (pin 15). The reference current Iref that passes through R1 can be expressed as Iref in the following equation (6-1):

At the current output terminal (pin4), the output current as in equation(6-2) below I out is:

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44

Fig(6-5)

Procedure:

Part1: R-2 R network DAC:

1. Refer to the circuit diagram in figure 6-6(b) or figure ACS14-1 on ETEK ACS-3000-07 module.

2. Let SW I, SW2, SW3 and SW4 switch to 1 ("0" represents as GND, " 1" represents as "+5 V").

3. By using voltage meter to measure TP1 , TP2 , TP3, TP4, TP5 of R-2Rnetwork and output port of D/A converter (Vout) . According to the switching of SW 1, SW2, SW3 and SW4 in table 6-l, record the measured results in table 6-1.

Fig(6-6)

Part 2: DAC0800 unipolar voltage output

1. Refer to the circuit diagram in figure 6-7 or figure ACS 14-2 on ETEK ACS-3000-07 module.

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45 2. Set Jl , J2 and J3 be short circuit.

3. Calculate the step size and record the calculation in table 6-2.

In table 6-2, the binary values are used as the digital inputs, which" 0 “represents GND,” 1 “represents +5V.

4. Using equation (6-2) and equation Vout=I out *R3 to calculate the theoretical values of the output current I out and output voltage Vout (Rr = 4.7 k), then record in calculation in table 6-2.

5. Let J1 be open circuit, then connect the digital current meter to 11 for measuring the output current Iout. Finally record the measured results in table 6-2.

6. Remove the current meter and let J1 be short circuit. Using digital voltage meter to measure the output voltage (O/P). Then record the measured results in table 6-2.

Fig(6-7)

Part three: DAC0800 bipolar voltage output

1. Refer to the circuit diagram in figure 6-7 or figure ACS 14-2 on ETEK ACS-3000-07 module. Set J1 and J2 be short circuit, J3 be open circuit.

2. Calculate the step values and record the calculation in table 6-3.

3. In table 6-3, the binary values are used as the digital inputs, which 0 represents GND And 1 represents +5 V.

4. Using equation (6-2) to calculate I out and Ifs , then substitute I out and Ifs into equation

Vout=2*I out*R4- Ifs*R4 Find the theoretical value of output voltage Vout, finally record

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46 5. Let J1 and J2 be short circuit, J3 be open circuit. Using digital voltage meter to measure

the output voltage Vout , then record the measured results in table 6-3 .

6. Let J1 and J3 be open circuit, J2 be short circuit. Connect the digital current meter to J1, then measure the output current Iout . Finally record the measured results in table 6-3. 7. Let J2 and 13 be open circuit, J1 be short circuit. Connect the digital current meter on J2

to measure the output current Iout. Finally record the measured results in table 6-3 . 8. Calculate I out + I~out and record the measured results in table 6-3.

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48

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49 EXPERIMENT.7

Pulse Code Modulation (PCM)

Objectives:

 T o study the operation of a PCM encoder.  To study the operation of a PCM decoder.

 To consider reasons for using digital signal transmission of analog signals.

Equipment Required:

 ETEK-DCS-6000-03 module  Signal Generator  Oscilloscope  DC-Power supply

Prelab works:

Consider the sinusoidal test signal x(t)cos(2t)this signal is applied to a sampler operating at 10 sample per second followed by a 8 level quantizer with a range of (-1, +1).the quantized samples are then applied to a natural binary encoder. (i.e, one that assigns 000 to the first level and 111 to the eight levels).

a. Plot x(t) for 0t1

b. Find the values of the sampled signal over0t1 c. Find the quantized values of x(t) for0t1

d. Find the sequence of binary digits observed at the encoder output for0t 1

Theory:

Pulse-code modulation (PCM) is a digital representation of an analog signal where the magnitude of the signal is sampled regularly at uniform intervals, then quantized to a series of symbols in a digital (usually binary) code. PCM has been used in digital telephone systems and is also the standard form for digital audio in computers.

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Block diagram of PCM modulator:

Demodulation of PCM:

To produce output from the sampled data, the procedure of modulation is applied in reverse. After each sampling period has passed, the next value is read and the output of the system is shifted instantaneously (in an idealized system) to the new value. As a result of these instantaneous transitions, the discrete signal will have a significant amount of inherent high frequency energy, mostly harmonics of the sampling frequency To smooth out the signal and remove these undesirable harmonics, the signal would be passed through analog filters that suppress artifacts outside the expected frequency range (i.e: greater than, the maximum resolvable frequency). Some systems use digital filtering to remove the lowest and largest harmonics. In some systems, no explicit filtering is done at all; as it's impossible for any system to reproduce a signal with infinite bandwidth, inherent losses in the system compensate for the artifacts — or the system simply does not require much precision. The sampling theorem suggests that practical PCM devices, provided a sampling frequency that is sufficiently greater than that of the input signal, can operate without introducing significant distortions within their designed frequency bands.

The electronics involved in producing an accurate analog signal from the discrete data are similar to those used for generating the digital signal. These devices are DACs (digital-to-analog converters), and operate similarly to ADCs. They produce on their output a voltage or current (depending on type) that represents the value presented on their inputs. This output would then generally be filtered and amplified.

There are many conditions for any PCM system:

 Choosing a discrete value near the analogue signal for each sample (quantization error must be minimum)

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51

 Sampler should operate at a rate of fs 2w

 Absolute error less than

2

where is the step of the quantizer, and n is the number of bits per sample.

 If 2Ais the peak to peak variation of the message signal and Q is the number of quantization levels, then

Q A 2   where Q 2n

The above fig represent a uniform quantizer with A=4v,Q=8.

1 8 8   

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Procedure:

Consider the circuit diagram in figure 7-1 in ETEK DCS-6000-03 module.

Fig (7.1)

1. Set J1 short circuit and from the signal input terminal (I/P), connect the signal generator and Set the amplitude of the sinusoidal signal 5 vp-p and 500Hz frequency.

2. Connect the oscilloscope to observe on the output terminal of low-pass filter (Tl), input terminal of audio signal (T2), feedback point of output signal (T3) and output signal Terminal of PCM (OP). After that connect the output terminal (T4) with2048 kHz square wave to the CH1 of the oscilloscope and output terminal (T6) of modulated signal to CH2 of the oscilloscope, then Draw the output of each terminal and determine the amplitude and the frequency of each output.

Consider the circuit diagram in figure 7-2 in ETEK DCS-6000-03 module.

Fig (7.2)

3. Set J1 of DCS6-1 short circuit and connects the output terminal (PCMO/P) of modulated PCM signal of DCS5-1 to the input terminal (PCM I/P) of demodulation PCM signal of DCS6- 1. By

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53 using oscilloscope, observe on the output terminal of buffer (TI), 2048 kHz square wave generator (T2), 8 kHz square wave generator (T3), demodulated PCM signal output Terminal (T4) and signal output terminal (Audio O/P), then record the measured results and draw each output and determine the frequency and the amplitude for each output.

4. Repeat step (1-3) when the frequency of the function generator change to 1 KHz.

5. Set J2 short circuit and J1 open and from the signal input terminal (I/P), connect the signal generator and Set the amplitude of the sinusoidal signal 5 vp-p and 500Hz frequency.

6. Connect the oscilloscope to observe on the output terminal of low-pass filter (Tl), input terminal of audio signal (T2), feedback point of output signal (T3) and output signal Terminal of PCM (OP). After that connect the output terminal (T4) with 2048 kHz square wave to the CH1 of the oscilloscope and output terminal (T6) of modulated signal to CH2 of the oscilloscope, then Draw the output of each terminal and determine the amplitude and the frequency of each output. 7. Set J2 of DCS6-1 short circuit and J1 open and connects the output terminal (PCM O/P) of modulated PCM signal of DCS5-1 to the input terminal (PCM I/P) of demodulation PCM signal of DCS6- 1.

8. connect the oscilloscope, observe on the output terminal of buffer (TI), 2048 kHz square wave generator(T2), 8 kHz square wave generator (T3), demodulated PCM signal output Terminal (T4) and signal output terminal (Audio O/P), then record the Measured results and draw each output and determine the frequency and the amplitude for each output.

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54 EXPERIMENT.8

TDM Multiplexer and Demultiplexer

Objectives:

 To understand the operation theory of Time Division Multiplexing TDM and Demultiplexing.

 To design and implement the TDM multiplexer and Demultiplexer.

Equipment Required:

ACS9-1 and ACS10-1 of ETEK ACS-3000-05 module.

DC Power Supply.

Connection wires.

Theory:

Time Division Multiplexing TDM:

TDM means multiple signals can be transmitted over the same transmission channel. Time division indicates the signal is divided into several slots in time domain, and then these slots will transmitted to the receiver by following a fixed time slots. Therefore, these slots are also called as sampling values. If the fixed time slot is large enough for other sampling value of other signal to fill in, then this method can achieve the function of multiplexing. The basic structure of TDM system is shown in figures 8.1 and 8.2 below:

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Fig(8.2): Circuit structure of TDM system.

The implementation of the TDM Multiplexer:

As a result of TDM uses the same channel to transmit several group of signals .Therefore, in this experiment we utilize sinusoidal, square and triangle waves as the several groups of signals to achieve the TDM modulation.

Since the TDM uses the time slots to transmit signal so we need to produce a time generator circuit (shown in fig 8.3) which can generate a fixed timing as the switching circuit.

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Fig(8.4): Time sequence of time generator.

The fig (8.5) shows the circuit diagram of TDM multiplexer. When t1 is high the triangular wave will occur at the output port while when t2 is high then the square wave will be at the output port and when t3 is high the output will be the sinusoidal wave.

Fig(8.5): Circuit diagram of TDM multiplexer.

TDM Demultiplexing:

After we divided the time of transmission channel into several time slots, there will be a small gap between each time slots which is known as guard time and it is used to prevent the interference between the symbol and jitter of the multiplexer. Therefore, we can utilize the pulse at a certain period to process different number of channels. On the other hand, according to the synchronous signal at the transmitter, the receiver can also separate the signals of different channels accurately. The example of a simple TDM system is shown below in fig (8.6).

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Fig(8.6): Transmission diagram of TDM system.

The implementation of the TDM Demultiplexer:

Fig (8.3) is also used as a synchronous signal generator for Demultiplexing. The most important thing is the synchronization between both time generators in the transmitter and receiver so the system will be able to recover the original signal. Fig (8.7) is the circuit diagram of TDM demultiplexer. When TDM signal inputs by matching with the synchronous signal generator, then we can obtain the input sequences which are the triangle, square and sinusoidal waveforms.

Fig(8.7): Circuit diagram of TDM demultiplexer.

Procedure:

TDM Multiplexing:

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58 1- By using oscilloscope, observe the output signal of triangular wave output port (TP1), adjust the variable resistor VR3 so that the amplitude of TP1 is maximum without distortion. Record your result.

2- Observe the output signal of square wave output port (TP2), adjust the variable resistor VR1 so that the amplitude of TP2 is maximum without distortion. Record your result. 3- Observe the output signal of sine wave output port (TP3), adjust the variable resistor VR3

so that the amplitude of TP3 is maximum without distortion. Record your result.

4- Turn the variable resistor “Clock Adj.” left to the end, at this moment the counter of the clock is slow. By using CH1 of the oscilloscope, observe the output signal of the triangular wave at port (TP4) .Use CH2 to observe TDM output port (TDM O/P). Record your result.

5- By using CH1 of the oscilloscope, observe the output signal of the square wave at port (TP5) .Use CH2 to observe TDM output port (TDM O/P). Record your result.

6- By using CH1 of the oscilloscope, observe the output signal of the sine wave at port (TP6) .Use CH2 to observe TDM output port (TDM O/P). Record your result.

TDM Demultiplexing:

Refer to figure ACS10-1 of ETEK ACS-3000-05 module.

1- Connect the output port (TDM O/P) of TDM multiplexer in ACS9-1 to the input port (TDM I/P) of TDM demultiplexer in ACS10-1.

2- Observe the output signal of (TP1) of TDM demultiplexer. Record your result.

3- Connect the triangular wave output port (TP4) of TDM multiplexer to (TP2) of TDM demultiplexer.

4- Connect the square wave output port (TP5) of the TDM multiplexer to the square wave input port (TP3) of the TDM demultiplexer.

5- Connect the sine wave output port (TP6) of the TDM multiplexer to the sine wave input port (TP4) of the TDM demultiplexer.

6- Using the oscilloscope to observe the signals at (TP2) and (O/P1) of the TDM demultiplexer.

7- Again use CH1 and CH2 of the oscilloscope to observe (TP2) and the square wave output port (O/P2) of the TDM demultiplexer.

8- Also observe both (TP2) and the sine wave output port (O/P3) of the TDM demultiplexer. 9- Use the oscilloscope to observe (TP3) and the output signal of triangular wave output

port (O/P1) of the TDM demultiplexer.

10- Observe again (TP3) and the output signal of square wave output port (O/P2) of the TDM demultiplexer.

11- Observe again (TP3) and the output signal of sine wave output port (O/P3) of the TDM demultiplexer.

12- Use the oscilloscope to observe (TP4) and the output signal of triangular wave output port (O/P1) of the TDM demultiplexer.

13- Observe again (TP4) and the output signal of square wave output port (O/P2) of the TDM demultiplexer.

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59 14- Observe again (TP4) and the output signal of sine wave output port (O/P3) of the TDM

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60 EXPERIMENT.9

Amplitude Shift Keying (ASK)

Objectives:

 Creation of ASK an modulated signal

 Detection of the modulated signal using envelope detector

 Detection of the modulated signal using bandpass filter followed by an envelope detector

Equipment Required:

 TPS3-3431  Power supply  Banana wires

Theory:

The general block diagram that represent the generation of ASK signal given bellow

The bit stream consists of a sequence of binary digits as demonstrated below for the sequence (10110100):

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61 The data after multiplication with a carrier [vcos(2pifct)] is an ASK signal as the following:

The detection of an ASK signal is done using envelope detection as the follows:

Refer to envelope detection of AM signal

Try to find the output after each stage of envelope detector.

Note it is not enough to do detection using envelope detector you must use two Schmitt trigger to convert the analogue output to digital output.

The output after the two Schmitt trigger must be as the following (in the case of perfect data recovery):

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62

Demodulation process using non-coherent demodulator:

Disadvantage of ASK modulated signal

1. Amplitude not constant this causes the detection process to be very difficult. 2. Usable only for Low data rate .

Remarks:

The spectrum of ASK signal resembles that of Normal AM modulation.

Procedure:

 Connect the trainer to the power supply.

 Connect the power supply to the Mains and turn it ON.

 Connect the data transmitter output to the ASK modulator input

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63  Connect the CH1 scope probe to the modulator input.

 You should see the transmitted data on channel CH1.

 Set the switches to the binary number 0101010 1 and watch the transmitted Data signals.  Connect the CH2 scope probe to test point TP 1.You should see the Fl carrier wave.  Measure or calculate the frequency of the carrier wave.

 This frequency should be approximately 12 KHz.

 Move the output of the CH2 scope probe to the modulator output.  In your notebook, draw the shape of the signals - the modulator (at the Modulator input) and the signal at the modulator output.

 Connect the modulator output to the envelope detector input.

 Move the CH2 scope probe from the modulator output to the detector's Output.  Decrease the time base a little in order to see more FI cycles during Transmission.  Because of the low sampling rate, you can notice only some of the F1Cycles.

 In your notebook draw the shape of the signals-the modulated signal (at the detector input) and the output of the detector.

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64  Move channel 2 of the scope probe from the detector output to the amplifier output.  In your notebook draw the shape of the signals-the modulated signal (at the detector

input) and the signal at the amplifier output..

 Connect the output of the ASK modulator to the input of the bandpass filter(BPF)

 Connect channel 2 of the scope probe to the filter input.  Draw the filter input

 Connect channel 2 of the scope probe to the output of the filter  Draw the output of the filter

 Connect the filter output to the envelope detector input

 Connect the detector output to the upper Schmitt amplifier input  Connect the Schmitt trigger1 output to the Schmitt trigger2 input  Connect the Schmitt trigger2 output to the data receiver input

References

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