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

Abstract

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-μm complementary metal–oxide–semiconductor (CMOS) with a 400-fF compensation capacitor occupies 900-μm2 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 μW 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.

Classification and Design Space Exploration of Low-Power Three-Stage Operational Transconductance Amplifier Architectures for Wide Load Ranges

“…The amplifiers in [51,52] achieve pseudo single-stage behavior by reducing the impedance of inner amplifier nodes to push the non-dominant poles to high frequencies. The required DC gain is restored by using shunt gain booster circuits, as shown in Figure 9.…”

“…Architectures that rely on reverse nested Miller provide an improved power efficiency [3,13,[29][30][31][32][33] but it has been recognized that nesting Miller capacitors leads to bulky and slow implementations and many architectures were devised to use a single Miller capacitor along with some ancillary compensation structures [4,11,14,[34][35][36][37][38][39][40][41][42][43][44][45][46][47][48]. Some authors have also demonstrated compensation techniques that do not rely on a Miller capacitor at all [8,[49][50][51][52].…”

Design of a 1 ampere high-precision thin-film resistive current transducer with negligible frequency dependence from DC to 100 KHz

“…Typical requirements for the sensors are a simple structure, wide bandwidth, reliability, low-Temperature Coefficient of Resistance (TCR), low self-heating, and robustness in sensing environment. In the case of transducers, is required a high precision interface insensitive to load and excellent stability from DC to kHz range [1][2][3][4][5][6][7].…”