A Compact Operational Amplifier with Load-Insensitive Stability Compensation for High-Precision Transducer Interface

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-mu m complementary metal-oxide-semiconductor (CMOS) with a 400-fF compensation capacitor occupies 900-mu m(2) chip area and achieves 0.022-2.78-MHz unity gain bandwidth and over 65 degrees phase margin with a load capacitance of 0.1-15 nF. The prototype amplifier consumes 7.6 mu 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.