A Low Power 2.4 GHz Variable-gain Low Noise Amplifier for Wireless Applications
SIMULATION RESULTS
The VGLNA was simulated, targeting 2.4 GHz using 0.18 um CMOS process. The VGLNA exhibited gain, S21 centred
at 2.4 GHz with a controllable range from 8.27 dB to 16.95
dB and it consumed 4.63 mW from a 1 V supply. The gains of the VGLNA are shown in Figure 8 with two modes. With
the current mirror as variable gain stage, the gain over power
quotient which was frequently used as a figure of merit for low power design was calculated to be 3.66 dB/mW.
Changes at the gain did not degrade the noise performance of the circuit since the circuit was constructed from two
different stages. As shown in Figure 9, the noise figure (NF) equalled to 1.05 dB. The input and output reflection coefficients were –27.40 dB and –22.98 dB, respectively, as shown in Figure 10. This showed that the VGLNA was able to provide enough attenuation to the LO leakage. In terms of linearity fulfilment, the input-referred third order intercept
point (IIP3) was –1.39 dBm with the gain optimized. This showed that the current mirror introduced for variable gain
in the VGLNA design reduced the current consumption of the circuit without sacrificing linearity.
Table 2 showed the summary of this work and comparison
with published data of several LNAs designed in CMOS
process. It was observed that this work demonstrated the
lowest noise figure (NF) with a power consumption of 4.63
mW.
CONCLUSION
This work demonstrated a variable gain low noise amplifier (VGLNA) in a 0.18 um CMOS process which was suitable for use as a first amplifier in Bluetooth application. As
the CMOS process keeps progressing to smaller channel
M1 NMOS M2 NMOS M3 NMOS M4 NMOS Lg L Ld L Ls L Lo L Co C Rbias R RFin Vb RFout Vdd I4 I3
L. Lee et al.: A Low Power 2.4 GHz Variable-gain Low Noise Amplifier for Wireless Applications
67
lengths driven by the digital circuitry, the performance of the circuits would continue to improve as well. Theoretical
analysis of the amplifier architecture demonstrated the
fundamental role of induced gate noise as well as in designing a power constrained noise optimization design.
This VGLNA exhibited 16.95 dB gain, 1.05 dB NF and
approximately 8 dB gain tuning range while dissipating
4.63 mW from a 1 V supply. The proposed VGLNA offers
a compromise between gain, noise factor and power consumption. Its versatility offers further deployment in circuits and architecture breakthrough especially in the wireless applications. 20 15 10 5 0 –5 –10 1.8 2.0 2.2 2.4 Frequency (GHz) S21 (dB) 2.6 2.8 3.0 1.5 1.4 1.3 1.2 1.1 1.0 1.8 2.0 2.2 2.4 Frequency (GHz) nf (2) 2.6 2.8 3.0
Figure 8. Power gain, S21 of the proposed VGLNA.
Figure 9. Noise figure of the proposed VGLNA in low and high gain modes.
ASM Science Journal, Volume 3(1), 2009
ACKNOWLEDGEMENTS
This research was supported by Silterra Malaysia Sdn. Bhd and Ministry of Science, Technology and Innovation
(MOSTI) of Malaysia through the National Science Fellowship (NSF).
Date of submission: September 2008 Date of acceptance: August 2009
REFERENCES
Allen, PE and Holberg, DR 2002, CMOS analog circuit design, Oxford University Press, USA.
Cheng, KH and Jou, CF 2005, ‘A novel 2.4 GHz LNA with digital gain control using 0.18/spl um/m CMOS,’ in Asia- Pacific Microwave Conference Proceedings 2005, vol. 2, pp. 4–7.
Lee, TH 1998, The design of CMOS radio frequency integrated circuit, Cambridge University Press, Cambridge.
0 –5 –10 –15 –20 –25 –30 1.8 2.0 2.2 2.4 Frequency (GHz) dB [S(1,1)] dB [S(2,2)] S1 1, S22 (dB) 2.6 2.8 3.0
Figure 10. S11 and S22 of the proposed VGLNA.
Table 2. Comparison of proposed VGLNA with VGLNAs published.
Process Frequency VDD Gain Gain NF Pdc Gain/Pdc
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0.18 5.75 1.8 21.00 10.5 4.40 22.20 0.95 (Raja et al. 2003)
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Elemental analysis of metals is usually necessary in order to study human health, environmental, geochemical and industrial issues (Vandercasteele & Block 1993). The effects of these elements on human health are of great interest nowadays, especially for consumable aquatic products because once toxic metals reach human beings they may produce chronic and acute illnesses (Reis & Almeida 2008).
Uluozlu et al. 2007 reported that metals could be possibly
classified as potentially toxic (arsenic, cadmium, lead,
mercury, etc.), probably essential (cobalt, nickel, vanadium) and essential (copper, iron, manganese, zinc). The toxic elements can be very harmful even at low concentrations if ingested over a long period of time. On the other hand, essential metals could produce toxic effects if their intake was excessive (Celik & Oehlenschlager 2007). As a result, it is not surprising that numerous studies have been carried
out on metal accumulation in different fish species, as fish
forms a major part of human diet (Türkmen 2005).
Quantification of metals in organic matter like fish is most
often accomplished via atomic absorption spectroscopy (AAS). This generally requires destruction of the sample matrix to produce a solution of the analyte for analysis. The decomposition of the sample is a critical step as it will
definitely have crucial effects on the final results. Therefore
it has to be assured that there is total decomposition of the
sample, with no significant loss of the metals throughout
the process. There is a wide range of sample decomposition methods for aquatic products that have been published,
such as dry ashing, wet ashing with different mixtures of reagents or conventional heating procedures, microwave dissolution and acid bomb digestion (Reis et al. 2008; Hseu 2004; Tüzen 2003 & Sures et al. 1995). These methods generally show both good accuracy and precision. However, the conventional wet and dry ashing digestion procedures are, to a certain extent rather time consuming.
The most commonly used method nowadays is microwave digestion which has been the method of choice that has offered many advantages over conventional digestion procedures in both time and recovery aspects. At present, a large number of methods are recommended for the preparation of aquatic samples via microwave assisted digestion with the addition of other reagents besides nitric acid (HNO3) prior to digestion of aquatic products (Hamilton
et al. 2007; Mendil & Uluözlü 2007; Manutsewee et al.
2007; Retief et al. 2006; Scancar et al. 2004). The addition of other reagents with HNO3 prior to digestion may permit more complete oxidation of organic sample matter, address
specific decomposition of required chemicals, or address specific elemental stability and solubility problems (EPA
Method 3052, 1996). Microwave extraction using diluted
acids in a closed high-pressure vessel at temperatures above the boiling point of these acids is a simple alternative sample preparation and its use is growing. Diluted mineral acid solutions can absorb microwave energy more intensely owing to their water content. These features reduce acid consumption, contamination, and preparation time (Soylak
et al. 2007). However, these may well cause limitation
to the technique or increase the complexity of analysis.