Design and implementation of a low-noise high-linearity variable gain amplifier for high speed transceivers

Abstract: The variable gain amplifier (VGA) is utilized in various applications of remote sensing and communication equipments. Applications of the variable gain amplifier (VGA) include radar, ultrasound, wireless communication and even speech analysis. These applications use the variable gain amplifier (VGA) to enhance dynamic performance. The purpose of the thesis work is to implement a high linearity and low noise variable gain amplifier in 150 nm CMOS technology, for an analog-front-end of a transceiver. Two different amplifier architectures are designed and compared. First architecture is an amplifier with diode connected load and second architecture is a source degenerative amplifier. The performance of the amplifier with diode connected load is lower than the source degenerative amplifier in terms of gain, power, linearity, noise and bandwidth. So, the source degenerative amplifier is selected for implementation. The three stage variable gain differential amplifier is implemented with selected architecture. The implemented three stage variable gain differential amplifier have gain range of -541.5 mdB to 22.46 dB with step size of approximately 0.3 dB and total gain steps are 78. The -3 dB bandwidth achieved is 953.3 MHz. The third harmonic distortion (HD3) is -45 dBc at 250 mV and the power is 35 mW at 1.8 V supply source.