Miller compensated four-stage OTA with Q-reduction for wide range of load capacitors

Abstract

This paper proposes a four-stage miller compensated Operational Transconductance Amplifier (OTA) with Q-reduction. The multi-stage OTA is an ideal choice for the submicron CMOS technology. The main challenge in multi-stage OTA design with low quiescent current is the increased number of high impedance nodes. These high impedance nodes create stability issues. Usually, the multi-stage OTA requires the compensation capacitor in the order of pF which consumes more chip area; moreover, it reduces the bandwidth of the OTA. The proposed four-stage OTA uses a single miller capacitor Cm along with a feed-forward capacitor Cf. The four-stage OTA uses only 500fF of total compensation capacitors to stabilize a complex four-stage OTA. The proposed OTA uses multiple feed-forward paths to enhance the small-signal and the large-signal performances of the OTA. The four-stage OTA achieves a better transient response with the settling time of 510ns under low quiescent power of 63.6μW for the wide range of load capacitors of 5pF to 100pF.