Optimization of Operational Amplifier Settling Time by Adjusting Secondary Poles Based on gm/ID Design

In readout circuits of infrared detectors, the settling time of the operational amplifier is crucial to transfer radiation signals. Hence, this paper proposes an optimization of the sizes of the load transistors pair, M3 and M4 in Figure 1, to improve the transient response. In this design, the amplifier is firstly designed based on g(m)/I-D method to satisfy the required performance. However, this may be not the best solution. Then, the sizes of the load transistors are scanned with the fixed width-to-length (W/L) ratio to guarantee the noise level. The step response experiments are carried out to figure out the best damping factor. Meanwhile, this paper analyzes the influence of the doublet spacing and the secondary pole-to-pole spacing. The initial calculated design has a settling time of 39.8ns @ 12 bit precision, while the settling process compresses to 32.4ns after the adjustment.