Abstract
In this paper, we present modifications to the constant-g m bias circuit and Miller-lead compensation of operational amplifiers which eliminate or minimize some of their shortcomings. First, we demonstrate how parasitic pad capacitance can cause instability in the constant-g m bias circuit, and show that the transconductance is constant only for specific bias conditions. Next, we suggest a new circuit topology that requires 75% less compensation capacitance to achieve stability. We also discuss problems with Miller-lead compensation that arise from temperature, process, and load variations. Finally, we present a new biasing technique to correct these problems, and, through simulation, demonstrate a 40∘ improvement in phase margin over load current variations.
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