A Compact Operational Amplifier with Load-Insensitive Stability Compensation for High-Precision Transducer Interface
2018
High-resolution electronic interface circuits for transducers with nonlinear capacitive impedance need an operational amplifier, which is stable for a wide range of load capacitance. Such operational amplifier in a conventional design requires a large area for compensation capacitors, increasing costs and limiting applications. In order to address this problem, we present a gain-boosted two-stage operational amplifier, whose frequency response compensation capacitor size is insensitive to the load capacitance and also orders of magnitude smaller compared to the conventional Miller-compensation capacitor that often dominates chip area. By exploiting pole-zero cancellation between a gain-boosting stage and the main amplifier stage, the compensation capacitor of the proposed operational amplifier becomes less dependent of load capacitance, so that it can also operate with a wide range of load capacitance. A prototype operational amplifier designed in 0.13-
μ
m complementary metal–oxide–semiconductor (CMOS) with a 400-fF compensation capacitor occupies 900-
μ
m
2
chip area and achieves 0.022–2.78-MHz unity gain bandwidth and over 65
∘
phase margin with a load capacitance of 0.1–15 nF. The prototype amplifier consumes 7.6 μ
W from a single 1.0-V supply. For a given compensation capacitor size and a chip area, the prototype design demonstrates the best reported performance trade-off on unity gain bandwidth, maximum stable load capacitance, and power consumption.
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