A Negative Resistance-Based ULV Variable-Gain OTA for Low-Power Applications

In this brief, a new low-power and low-voltage configurable-gain small-signal amplifier is proposed. It is based on an active negative resistance circuit and incorporates an improved technique for controlling output common-mode voltage stability in all gain range using a replica bias strategy. The circuit modeling and sizing procedure are described, as well as a prototype version in 180-nm CMOS process for operation with a supply voltage of 0.4 V. The measurement results demonstrate the ability to provide variable gain from 3 to 22 dB for a unity gain frequency of 55 kHz with power consumption in the range of 94 to 549 nW. The performance is comparable to that of state-of-the-art low-voltage variable-gain amplifiers, with the advantage of requiring less silicon area.