A 0.35-V bulk-driven self-biased OTA with rail-to-rail input range in 65 nm CMOS

An operational-transconductance-amplifier (OTA) design for low-voltage low-power applications is proposed. The proposed OTA incorporates bulk-driven MOS transistors in the pseudo differential pair of the input stage to concurrently enable low voltage operation and rail-to-rail input range. Using a common-mode feedforward (CMFF) circuit in the first stage to bias the following stages of the OTA obviates the need for extra biasing circuitry and improves the performance of the OTA. To further enhance the bandwidth and allow the use of smaller compensation capacitors, a compensation network based on a damping factor control circuit is exploited. To verify the theoretical findings, the OTA was fabricated in a 65 nm CMOS technology. Measurements show that the OTA provides a low-frequency gain of 46 dB at V_DD = 0.5 V, and a gain of 43 dB at V_DD = 0.35 V. The power dissipation is 182 μW at V_DD = 0.5 V, and 17 μW at V_DD = 0.35 V.