Hybrid Cascode Compensation for Two-Stage CMOS Opamps

Abstract

This paper presents the analysis of hybrid cascode compensation scheme, merged Ahuja and improved Ahuja style compensation methods, which is used in two-stage CMOS operational transconductance amplifiers (OTAs). The open loop signal transfer function is derived to allow the accurate estimation of the poles and zeros. This analytical approach shows that the non-dominant poles and zeros of the hybrid cascode compensation are about 40 percent greater than those of the conventional cascode compensation. Circuit level simulation results are provided to show the accuracy of the calculated expressions and also the usefulness of the proposed cascode compensation technique.

A 5th-order ΣΔ modulator with combination of op-Amp and CBSC circuit for ADSL applications

“…As shown in Fig. 7, a 2-stage folded-cascade class A OTA is employed to implement the IIR filter block [15]. In this structure, in addition to C s compensation capacitor, the C a capacitor is employed to keep circuit poles further away from zero frequency in order to attain higher rate and bandwidth with respect to conventional structures.…”

A new class AB folded-cascode operational amplifier

“…Thus, a two-stage class AB amplifier with large slew rate and enhanced unity-gain bandwidth and DC gain is achieved. To further improve the linear settling performance of such a two-stage class AB amplifier, the hybrid cascode compensation can be utilized [4].…”

Design of a two-capacitor sample & hold circuit using a two-stage OTA with hybrid cascode compensation

“…Frequency compensation plays an important role in design of a stable two-stage opamp, the most well known of which are Miller and cascode. The main drawbacks of Miller compensation scheme are the low speed and low power supply rejection ratio (PSRR) compared to the cascode compensation [5].…”

“…We use a novel cascode compensation scheme called hybrid cascode compensation that has been introduced in [4] and reconsidered in [5,6]. In this method, two distinct capacitors are used between two low-impedance nodes of the first stage and the output node.…”

“…As shown in Fig. 2 two separate capacitors, C a and C s , have been used for compensation of the opamp where C a is used in a signal path and C s in a non-signal path [5,6].…”