A Low-Noise Area-Efficient Current Feedback Instrumentation Amplifier

Abstract

The low-power current feedback instrumentation amplifier (CFIA) circuits using local feedback configuration are reported in the literature for biomedical applications. However, they have limitations such as low gain, higher area, and higher noise due to the need for higher source degeneration resistors (in tens to hundreds of kΩ), and higher minimum achievable bandwidth (in tens of kHz). In this paper, a low-power, low-noise CFIA using closed-loop configuration is proposed to overcome these limitations. It uses a folded cascode operational transconductance amplifier with a lower value of source degeneration resistor (in the order of few kΩ) in the input stage to reduce the noise without compromising the loop gain. As the bandwidth of the proposed CFIA is defined as unity-gain bandwidth of the CFIA’s loop gain, it can be reduced below 10 kHz without increasing area. The proposed CFIA is designed and implemented in a 0.35 µm CMOS process for a current of 9.6 µA with a supply voltage of 3 V, and its performance is evaluated through simulation. It has a gain of 34 dB, total input-referred noise of 3 µVrms, and a noise efficiency factor of 3.81. It achieves a bandwidth of 8.8 kHz using a load capacitor which is more than four times smaller than that of local CFIA. It provides an input signal swing of 16 mVpp at THD of 1% and the CMRR of 118 dB.