Study of Small-signal Model of Simple CMOS Amplifier with Instability Compensation of Positive Feedback Loop

The paper deals with precise analysis of simple AC variable gain CMOS amplifier. The circuit can be used as a simple voltage follower (6 MOS transistors are required) or amplifier. The main attention of this work is focused on a small-signal model of the proposed block and effects of additional passive network leading to compensation of its instability. The continuous gain adjusting in range from 1.1 to 10 (0.8 – 20 dB and with bandwidth 4.9 - 90 MHz at 5 pF load capacitance) is possible and the proposed amplifier is suitable for implementation in systems, where lower range of gain adjusting and large dynamical range is required. Theoretical analyses are supported by PSpice simulations (TSMC 0.18 um technological models) and experimental measurements with commercially available CMOS transistor fields (ALD1106/7) also confirm the discussed behavior of the amplifier.