A 1.87 µW Capacitively Coupled Chopper Instrumentation Amplifier with a 0.36 mV Output Ripple and a 1.8 GΩ Input Impedance for Biomedical Recording

Abstract

Chopper and capacitively coupled techniques are employed in instrumentation amplifiers to create capacitively coupled chopper instrumentation amplifiers (CCIAs) that obtain a high noise power efficiency. However, the CCIA has some disadvantages due to the chopper technique, namely chopper ripple and a low input impedance. The amplifier can easily saturate due to the chopper ripple of the CCIA, especially in extremely low noise problems. Therefore, ripple attenuation is required when designing CCIAs. To record biomedical information, a CCIA with a low power consumption and a low noise, low output ripple, and high input impedance (Zin) is presented in this paper. By introducing a ripple attenuation loop (RAL) including the chopping offset amplifier and a low pass filter, the chopping ripple can be reduced to 0.36 mV. To increase the Zin of the CCIA up to 1.8 GΩ, an impedance boost loop (IBL) is added. By using 180 nm CMOS technology, the 0.123 mm2 CCIA consumes 1.87 µW at a supply voltage of 1 V. According to the simulation results using Cadance, the proposed CCIA architecture achieves a noise floor of 136 nV/√Hz, an input-referred noise (IRN) of 2.16 µVrms, a closed-loop gain of 40 dB, a power supply rejection ratio (PSRR) of 108.6 dB, and a common-mode rejection ratio (CMRR) of 118.7 dB. The proposed CCIA is a helpful method for monitoring neural potentials.

Keywords

• low power
• chopper amplifier
• ripple attenuation
• input impedance