A High Gain, Low Offset Time-Based Operational Amplifier for Capacitive Loads with 36MHz UGB and 70μA Quiescent Current

A time-based operational amplifier (OP-AMP) with high gain and a wide bandwidth is presented in this paper. The proposed OP-AMP utilizes voltage-controlled oscillator (VCO) as an ideal integrator to replace the conventional voltage-based error amplifier which provides infinite DC gain. The OP-AMP is compensated with a feed-forward Gm amplifier with capability of driving load capacitance up to 200pF. Proposed OP-AMP uses only 2pF of on-chip capacitor and consumes low quiescent current (70μA at typical corner and temperature). It further utilizes time-based offset cancellation technique to reduce the effect of mismatch between VCOs. The proposed OP-AMP was designed in TSMC 65nm CMOS LP process technology with input/output common mode voltages as 0.3V-0.7V and input power supply of 1.2V; achieving unity gain bandwidth (UGB) of 36MHz. A case study involving reference buffer for a 12-bit SAR ADC and a track and hold circuit are presented to demonstrate the versatility and performance of the proposed OP-AMP.