High Slew Rate Op-Amp Using LHP Zeroes

Abstract

In this paper, to achieve a high slew rate (SR) Op-Amp, a new compensation method for a fully differential two-stage operational transconductance amplifier (OTA) is presented. The proposed technique adds a left half-plane (LHP) zero to the first stage of the two-stage class A-AB using a nulling resistor with a series compensating capacitor, improving the stability of the closed-loop configuration. Also, active compensation has been used, which also leads to an increase in gain. Thus, compensation is done with a smaller capacitor, and the operational amplifier slew rate is increased. The output stage is an AB amplifier class, and floating gate MOSFET is used as a large resistor in the second stage. The value of the load capacitor is assumed to 20 pF. The proposed circuit is simulated by HSPICE with 180 nm 3.3V CMOS technology. Simulation results show that the gain and average slew rate of the proposed operational amplifier is 94.2 dB and 12.6 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{V}/\mu\mathrm{s}$</tex> , respectively. However, the gain and average slew rate of the previous class A-AB operational amplifier is respectively 89 dB and 3.95 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{V}/\mu\mathrm{s}$</tex> in the same power consumption (0.33 mW) and load capacitor.