Hybrid Cascode Compensation With Hybrid Q-Factor Control for Three-Stage Unconditionally Stable Amplifiers

This paper presents Hybrid Cascode Compensation with Hybrid Q-Factor Control (HCCHQ), for three-stage feedback operational transconductance amplifiers (OTA) capable of handling any load capacitor (C-L). The design incorporates an enhanced Miller compensation strategy, exploiting cascode-Miller compensation with hybrid pathways to effectively separate the dominant pole from non-dominant poles for bandwidth expansion. It also combines a hybrid quality factor (Q-factor) control with a local impedance attenuation (LIA) module, adjusting the Q-factor of non-dominant poles by mitigating the ringing in the time response and the frequency peaking for lighter C(L)s. The new design can accommodate unlimited capacitive loads, owing to the Miller- and load-compensated solutions for the light and heavy C(L)s, respectively. Fabricated in a 180-nm standard CMOS process, a prototype of the proposed amplifier demonstrates a quiescent current of 25 mu A under a 1.8 V single supply. It boasts a compact 0.0055 mm2 area and exhibits unconditional stability when configured as a voltage buffer driving any CL. With a mean DC gain of 115 dB, the average unit-gain frequency (UGF) is 2.30 MHz and 0.11 MHz for 0.1 and 47 nF external capacitive loads, respectively. The mean 1% settling time is measured as 2.41 mu s and 40 mu s for the same capacitive loads, respectively, when a 0.4 V pulse signal is applied to the input.