Low-voltage high-linear Gm-transimpedance instrumentation amplifier with robust feedforward biasing against PVT variations

Abstract

A new gm-transimpedance instrumentation amplifier (GTIA) is introduced that enables precision signal acquisition with low-power operation. The GTIA architecture employs an input current-mode gm stage to achieve high-linearity and low-noise specs simultaneously. For biomedical applications, a bootstrapped AC coupling scheme is devised which maintains rail-to-rail electrode offset tolerance and gigaohms level input impedance. The amplifier gain is set by a single feedback resistor to over 80 dB with 2nd-order bandpass filter response. Also, an innovative feedforward biasing technique is proposed that yields robust operation along with adaption to different ranges of supply voltage. The circuit is implemented in 0.18 μm CMOS process and consumes 40 and only 1.12 μW of power at 1.2 and 0.8 V. Several simulations have been carried out to characterize the designed GTIA. Total input-referred noise equals 0.88 and 3.17 μVRMS within frequencies of 0.5–100 and 0.1–150 k Hz, respectively. Input offset voltage equals 2.6 μV regulated via the DC servo loop (DSL) circuit which does not degrade the noise performance. CMRR of the designed GTIA is up to 105 dB without sensitivity to variation of the feedback resistor and the THD is less than 0.015% for a 2 mVpp input signal.