A Single-Stage, Capacitively-Coupled Instrumentation Amplifier With Complementary Transimpedance Boosting

Capacitively-Coupled Instrumentation Amplifiers (CCIAs) are widely used as AC-coupled, low-noise amplifiers in many multi-channel, area-intensive sensor interface applications. However, the need for a trade-off between the front-end gain and CCIA area, imposed by the input capacitance, restricts the miniaturization of such sensors. We propose a Complementary Transimpedance Boosting (CTB) technique to relieve this challenging gain versus area trade-off. The proposed CTB applies to both the DC and AC paths of a CCIA. CTB also reduces AC gain degradation, suppressing low-side gain peaking of the frequency response without significantly increasing input-referred noise. The Gain-Noise-Area Efficiency (GNA) and Gain-Power-Area Efficiency (GPA) factors are also introduced for holistic comparisons with other front-end amplifiers regarding noise, gain, and power consumption. CTB-based CCIAs (CTB-CCIA) are fabricated in 0.18 <tex-math notation="LaTeX">μ</tex-math> m CMOS, with the highest single-stage AC gain of 289 V/V achieved. Occupying only 0.011 mm <tex-math notation="LaTeX">²</tex-math> , a conventional CCIA with the same area will have 14.4 <tex-math notation="LaTeX">×</tex-math> less gain while requiring at least two stages. The CTB-CCIA has a competitive NEF of 4.92 within a signal bandwidth of 0.21 Hz – 8.7 kHz, suitable for multi-channel applications.