A 0.5V Bulk-Input Operational Transconductance Amplifier with Improved Common-Mode Feedback

This paper presents the design of a two-stage pseudo-differential operational transconductance amplifier (OTA). The circuit was designed in a standard 0.18 mum, 0.5 V V_T digital CMOS process. An improved bulk-mode common-mode feedback (CMFB) circuit has been designed which does not load the OTA compared to previous design (Chatterjee, 2004). A self cascode load structure and partial positive feedback provide higher gain. The bulk terminals of all transistors have been biased to lower their V_t and maximize signal swing. The OTA operates at a supply voltage of 0.5 V and consumes only 28 muW of power. Rail-to-rail input is made possible by using the transistor´s bulk terminal as the input. For a load of 20 pF the OTA has a simulated DC gain of 65 dB, a gain-bandwidth product of 550 kHz, and a phase margin of 50⁰.