Step-response optimization techniques for low-power three-stage operational amplifiers for large capacitive load applications

This paper proposes and develops two simple efficient techniques for optimizing the closed-loop transient response of three-stage amplifiers for large capacitive load applications. The proposed approaches exploit a current comparator in the inner amplifier nodes to sense the input voltage transients and switch on an auxiliary driving device providing slew-rate enhancement and settling time improvement without extra static power dissipation. SPECTRE simulations are carried out on a three-stage amplifier adopting a recently proposed RNMC strategy with a voltage follower and two resistors. Simulation results confirm the effectiveness of both proposed techniques, showing a symmetrical step-response with a significant improvement in large-signal speed performance. Both discussed solutions are suitable for any particular three-stage amplifier topology and are also independent of the adopted compensation network.