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Measuring Signal Generator Response Through
An Adc Evaluation Board
Limuel R. Landicho, Irvin B. Garcia, Glenn N. Ortiz, Mark Joseph B. Enojas
Abstract Many semiconductor industries use Automated Test Equipment (ATE) which comprises of linear and mixed signals instruments. External Signal generators are usually not associated to the equipment’s calibration or checker routine. This research introduces a method of testing the functionality of the signal generators by establishing a signal generator checker for automated test equipment using Analog to Digital Converter (ADC) evaluation board and Field Programmable Gate Array (FPGA) capture board. This setup will enable the system to focus on fundamental frequency and amplitude level of the signal generator. A Visual Basic Application (VBA) program was created to control the desired frequency and amplitude level of the signal generator. The FPGA evaluates the digital signal and graphically presents it in a system data platform software. In result, the graphical output displays the quality of the signal generator through the full-scale fundamental frequency and amplitude levels. The common problems encountered using ATEs, namely; loosed RF cable, incorrect RF cable connections on ATE configuration, and noisy signal generators can be detected. This research is precedent to a more intelligent and complex signal generator checker to ensure signal integrity.
Index Terms: analog to digital converter, automated test equipment, device under test, field programmable gate array, signal generator, visual basic application
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1
INTRODUCTION
There are several means to ensure ATEs are working properly. Some methods of tests for ATEs are based on parameters such as reliability, maintenance, and testability [1]. It is vital to ensure that each of the test equipment used in ATEs are checked. Signal generators play an important role in providing RF signals to test equipment. Examples of such devices tested are nonlinear microwave devices where the phase and amplitude are critically monitored [2]. Signal generators need to be checked based on frequency and amplitude of signals. Frequency band from 500 kHz to 20 MHz can be tested using a simple crystal oscillator and high power amplifier [3]. The signal quality is evaluated based on the signal to noise ratio
and distortion (SINAD) given the formula of eq. (1), where PAll
is the total power of all signal components, P0 the component
power, and P1, the carrier power [3]. Common values of
SINAD for signal generators in these frequencies are in 130 dB.
For pulsed RF signals, the device under test (DUT) is being evaluated based on its amplitude and phase. Evaluation and verification for such signals are done using digital sampling oscilloscopes [4].
Another method of testing components in ATEs for RF signals is through matching networks. This method tries to address the degradation in RF signal. However, it can cover but not all the frequencies defined for such ranges [5]. Some model of a mobile signal viewer was developed for convenience [6]. However, interference is more felt in the airwaves, especially when mobile devices such as smart phones are used. Therefore, development of a more robust and reliable system needs to be established that is insusceptible to such interference or noise. In order to retain the integrity of signals, a method of signal transformation is needed [7]. The FPGA reinforces the integrity of digital signal measurement. [8]. In tests, debugging, and calibration of signal generators for ATEs, visuals and interface for engineers and technicians to the equipment or machine is a great advantage [6], [9], [10]. This paper presents a method of testing and measurement of the Signal Generators used for ATEs based on its fundamental frequency and amplitude level response from the instrument itself up to the test head. As an improvement, an excel VBA graphical user interface (GUI) was created to control the signal generator’s desired input frequency and amplitude level as well as the value of clock frequency based on the ADC evaluation board product specifications. An ADC evaluation board was used to convert the analog frequency signal into digital codes in lieu of the ADC voltage reference along with its complementary FPGA capture board that evaluates the results of the signal response of the signal generator. A system data platform was used to demonstrate the fundamental frequency and amplitude level response of the signal generator via graphical representation of the signal on a computer software. In addition, this study highlights an alternative application of ADC evaluation board, which is also used as a customer-based systems data analyzer to ensure that the product performs on the conditions set by the product specification data sheet. It is utilized to check the signal generator’s functionality by connecting the fundamental frequency and amplitude response which is defined by eq. (2) based on the full scale power response. The succeeding sections are discussed: Section 2, the methodology which explains the process flow and tests and evaluation, Sectionv3, presents and discusses the results of the tests, and Section 4, the concluding statement.
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• Limuel R. Landicho is a graduate of Bachelor of Science in Electronics and Communications Engineering in Technnological University of the Philippines Taguig, Philippines under the Industry-Based Program. E-mail: [email protected]
• Irvin B. Garcia is a graduate of Bachelor of Science in Electronics and Communications Engineering in Technnological University of the Philippines Taguig, Philippines under the Industry-Based Program. E-mail: [email protected]
• Glenn N. Ortiz is a graduate of Master of Technology Management in University of the Philippines Diliman, Quezon City Philippines, E-mail: [email protected]
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2
METHODOLOGY
2.1 Signal Generator Checker Process Flow and Design
The setup for the signal generator checker is presented in Fig. 1. A VBA GUI was developed for the control of the input signal to the signal generator. The desired frequency and amplitude levels for checking are inputted to the system and processed to the ADC evaluation board, thus signals are in 1’s and 0’s. This is evaluated further in a capture board via SPI controller. The generated fundamental frequency and amplitude level responses are graphically presented by the systems data analysis platform on a computer software
The desired signals will be fed to the signal generator and are also displayed in the GUI. This signals are transmitted through a GPIO module of the ATE test head and linked to the RF connector of the ADC evaluation board through a communication cable. At this point the signals are now
digitized and further evaluated to the FPGA and will undergo data analysis via USB connection. The software Visual Analog is used to adjust and set the amplitude of the input signal. The graph and standard data outlook of the signal generator response are displayed in the computer monitor. Varying the desired frequency and amplitude signal for checking can be done using this setup. The user can set parameter threshold to identify whether the signals passes or fails.
2.2 Software Design
The developed VBA program on ATE’s user interface is used to input the desired signals and display it in a GUI. The Visual analog and Serial Peripheral Interface (SPI) controller installed in the computer is used for system data analysis of the generated data. See Fig. 3. The SPI controller software facilitates the data transmission.
2.3 Project Testing and Evaluation
The tests are done based on the accuracy, reliability and functionality. The functionality test is in the context of the developed VBA GUI workability based on the signal generator output criteria: 1) signal generator input frequency and amplitude level congruence, 2) ADC evaluation board and Capture board evaluation in frequency set {100KHz, 1MHz, 3MHz, 5MHz, 8MHz, and 10MHz} with amplitude level range of 0dB, 2dB, 4dB, 6dB, and 8dB. The fundamental level response from the Visual Analog and SPI controller will be collected and tabulated. 3) ATEs Test head GPIO module tests. The congruence of the input frequency and the display in the GUI will be checked. To verify these signals, an oscilloscope is used for both the input and the clock port on the GPIO module.
3 RESULTS
AND
DISCUSSION
3.1 Hardware Design Results
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3.2 Software Design Results
The GUI contains the analog input frequency and the amplitude level display. The ―RUN‖ button is used to run the checking of the signal generator. The actual display of the developed GUI is presented in Fig. 5. To verify the display accuracy of the VBA GUI developed, it is compared to the signal generator frequency and amplitude level display. Series of trials are conducted to execute adjustments in software display resolution and accuracy. As a result, the display achieved a 100% accuracy in a resolution of 1Hz. The Visual Analog and the SPI are run to monitor the signal input and output. The digitized signals are fed to the SPI controller to facilitate the analysis and display of signals. See Fig. 6.
3.3 Test Results
1. Congruence of signals
To verify the congruence of signals, an oscilloscope is used.
The VBA GUI displays the input signal frequency and its amplitude in dB and is verified through the signal generator display and oscilloscope. See Fig. 7. The results of the signal generator frequency and amplitude levels are shown in Fig. 8 for the two ATEs. At frequencies of 100KHz, 1MHz, 3MHz, 5MHz, 8MHz, and 10MHz, which are within the bandwidth of the ADC evaluation board, have an output fundamental level at 0dB or full scale power. In general, it can be said that at any given frequency within the range of the ADC evaluation board, the output fundamental power amplitude can go to the minimum or maximum levels.
2. Testing cable connections
The testing of ATE cable connections can be verified using the Virtual Analog display. An incorrect setup was intentionally done. The instrument is connected to the GPIO module of the ATE to verify the ability of the system to identify incorrect connection. The result is shown in Fig. 9. A standard signal generator as the source of analog signal frequency and another signal generator as clock pulse source.
3. Evaluating ATEs
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can be used to classify good and bad signal generators. An additional test for cable connections was conducted. One case is an intentionally loosed connection. This is run in 10 MHz at 8dB input frequency in a good signal generator of an ATE. There is a noticeable drop of fundamental frequency in a loosed connection cable. The secured cable connection normally has fundamental frequency as shown in Fig. 14b. One special case that is considered when the fundamental frequency drops is due to aliasing or folding. This happens when the frequencies are much higher than 15 MHz which is presented in Fig. 15. This is one good reason why the tests are limited to such an amount of frequency. The setup is enough to be used to measure and classify good and bad signal generators.
4 CONCLUSION
In this research, a signal generator checker was established for Automated Test Equipment using ADC Evaluation Board and FPGA Capture Board through a VBA based GUI controls. The functionality and accuracy was tested based on cable connection quality from ADC evaluation board to ATE’s test head GPIO, configuration of Visual Analog and SPI controller software on the ADC evaluation board, and amplitude level on the ATE’s GUI based on ADC’s voltage reference. Using this setup in doing diagnostics on ATEs will be able to detect problems like loosed and incorrect RF cable connection to ATE and some noisy signal generators. Additional improvement can be done in the future for good quality tests and evaluation of equipment and products in this field. Single load board design of signal generator checker can be embedded on ATE’s test head. A sweep function for analog input frequency and amplitude of the signal generator on the VBA program can be added that is capable to operate from 9 KHz to 6 GHz. An intelligent evaluation board can be designed that is able to find fault with a data log window showing the frequency and amplitude based on the user-defined tolerance.
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ACKNOWLEDGMENT
This research is conducted to improve processes in the work environment when using ATEs. The equipment and products
used were provided by Analog Devices Inc. in partnership with TUP Taguig as the academic institution. The authors acknowledge the almighty God and our Lord Jesus Christ who made all these possible. In this research, a signal generator
checker was established for Automated Test Equipment using ADC Evaluation Board and FPGA Capture Board through a VBA based GUI controls. The functionality and accuracy was tested based on cable connection quality from ADC evaluation board to ATE’s test head GPIO, configuration of Visual Analog and SPI controller software on the ADC evaluation board, and amplitude level on the ATE’s GUI based on ADC’s voltage reference. Using this setup in doing diagnostics on ATEs will be able to detect problems like loosed and incorrect RF cable connection to ATE and some noisy signal generators. Additional improvement can be done in the future for good quality tests and evaluation of equipment and products in this field. Single load board design of signal generator checker can be embedded on ATE’s test head. A sweep function for analog input frequency and amplitude of the signal generator on the VBA program can be added that is capable to operate from 9 KHz to 6 GHz. An intelligent evaluation board can be designed that is able to find fault with a data log window showing the frequency and amplitude based on the user-defined tolerance.
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