Indian Journal of Science and Technology
Year: 2016, Volume: 9, Issue: 16, Pages: 1-7
Anu Ravindran*, Karthigha Balamurugan and M. Jayakumar
Department of Electronics and Communication Engineering, Amrita School of Engineering, Amrita Vishwa Vidyapeetham, Amrita University, Coimbatore – 641112, Tamil Nadu, India; [email protected], [email protected], [email protected]
*Author of Corresponding: Anu Ravindran Department of Electronics and Communication Engineering, Amrita School of Engineering, Amrita Vishwa Vidyapeetham, Amrita University, Coimbatore – 641112, Tamil Nadu, India; [email protected]
Background/Objectives: Now-a-days advancements in CMOS technology increase the demand on transceiver design in the aspect of gain, linearity, power, re-configurability and cost-effectiveness1 . The performance of RF frontend of transceiver system using MOS device are excellent and found to be the par of 3-5 semiconductor technology. Methods/Statistical Analysis: The first component present in transceiver design is Low Noise Amplifier (LNA) which requires high gain, low noise, better input-output matching, low power, good linearity and stability. Trade off between these performances is more complex when transistors operate at reduced supply voltage and reduced power consumption. So many researchers focus to modify the existing topology by adding active/passive feedback elements and/or using current re-use inductors2,3. But the latter, suffer from large power consumption. Moreover LNA using cascode configuration offers good gain with low power but the circuit has the limitation of output voltage swing4 . So the proposed work focuses on the design of LNA using transconductance feedback in Common Source (CS) configuration circuits. Findings: At RF frequencies, distributed parasitic of the device dominates thus altering the inputoutput matching characteristics which degrades gain, noise figure and stability of Low Noise Amplifier. So design of multistage LNA with feedback techniques is necessary to increase the gain. The transconductance feedback used in the design of LNA suits well for increase of gain provided if it is properly designed to ensure stability. The proposed work involves the design of MOS based low noise amplifier using single stage and cascaded Common Source (CS) configuration in S-band. By using the transconductance feedback in CS amplifier, the voltage gain is boosted. Using the extracted small signal equivalents, single stage and cascaded CS amplifier with the transconductance feedback are designed and analyzed. Importance of device parasitic like gate to source capacitance, gate to drain capacitance and the output resistance influence the loop gain. This is brought in the design and emphasizes on the proper utilization of these parasitic in LNA design with transconductance feedback. Using a standard 90 nm CMOS process, LNAs have been demonstrated for 2-GHz frequency (S-band) applications. Operated at a supply voltage of 0.6 V, the gain and noise figure of single stage CS LNA with transconductance feedback are observed to be 17.9 dB and 2.1 dB respectively. It is noted that nearly 17% gain improvement has been achieved with excellent input reflection coefficient of -54.8 dB and low power consumption of 2.92 mW. Similarly, for a cascaded CS amplifier when operated at 0.6V, it is observed that the gain and noise figure are found to be 13.6 dB and 2.38 dB respectively. It is noted that nearly 6.25% increase in gain is achieved with appealing reverse gain of -52. 8 dB when compared to cascaded CS circuit without transconductance feedback. Higher reverse gain ensures the stability of the designed amplifier. Applications: The proposed work is needed in the design of transceivers working at S-band (2 GHz – 8 GHz). Few noticeable applications are: Communication satellites (NASA), weather radar systems, microwave ovens and optical communication5 which require low power modules. Improvements: This work can be further extended to reconfigure the input matching network so that UWB bandwidth is covered.
Keywords: Cascaded Common Source (CS) Configuration, Low Noise Amplifier (LNA), MOS Parasitic, S-Band, Trasconductance Feedback
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