An ultra-low-power reconfigurable two-stage OTA with improved transconductance and DC gain

ABSTRACTAn ultra-low-power reconfigurable bulk-driven two-stage operational transconductance amplifier (OTA) with enhanced transconductance and dc gain is presented in this article. By means of the partial positive-feedback technique, the effective bulk transconductance of the input stage is improved. Also, the proposed composite-transistor is used to enhance the dc gain of the OTA. In addition, a proposed pseudo-cascode compensation technique to improve the stability of the two-stage OTA in ultra-low-voltage condition, which makes the OTA reconfigurable, is introduced. Transistor-level simulations in UMC 0.18μm CMOS process confirm the theoretical results. Simulated from a 0.5-V supply voltage, the proposed OTA achieves a 98 dB dc gain, a 15.5kHz gain-bandwidth and the phase margin varies less than 6% as the bias current scaled by a factor of 200. The power of the proposed OTA is only 38nW.