Slew Rate Enhancement Using Recycling Tail Current Source

Abstract

A current recycling structure is used to boost the tail current source of an operational transconductance amplifier (OTA), improving the slew rate (SR). The proposed current recycling circuit detects the magnitude of the differential input voltage and adjusts the tail current source value in proportion to the absolute value of the detected differential input voltage. When a small input signal is applied, the quiescent current of the OTA does not change; therefore the proposed tail current boosting circuit does not degrade the voltage gain and bandwidth. The proposed boosted tail current source has been used to drive a two-stage class A-AB OTA to evaluate its performance. Post-layout simulation results using standard 0.18 µm 3.3 V CMOS process technology show SR improvement of approximately 396% at the cost of 21% increase in static power consumption compared to a two-stage class A-AB primary OTA. The proposed AB-AB OTA achieves 65.7 V/μs at a static power consumption of 0.38 mW when driving a 10 pF capacitive load.