A Low-power and Low-noise Multi-purpose Chopper Amplifier with High CMRR and PSRR

Area of Science:

• Electronics
• Biomedical Engineering
• Signal Processing

Background:

• Neural signal acquisition requires amplifiers with high Common-Mode Rejection Ratio (CMRR) and Power Supply Rejection Ratio (PSRR).
• Low noise and wide bandwidth are critical for accurately capturing electroencephalogram (EEG), local field potential (LFP), and action potential (AP) signals.
• Existing amplifier designs often face trade-offs between noise, bandwidth, power consumption, and input impedance.

Purpose of the Study:

• To design and optimize a multi-purpose, low-noise chopper amplifier for various neural signal applications.
• To achieve high CMRR and PSRR while minimizing noise figure (NEF) and power consumption.
• To integrate features for DC offset rejection, high input impedance, and noise reduction for clear signal acquisition.

Main Methods:

• A single-stage current reuse amplifier with pseudo-resistor common-mode feedback was employed to minimize noise and increase bandwidth.
• A fully differential amplifier was used in the second stage for high output swing.
• A DC servo loop with an active RC integrator, a positive feedback loop for input impedance enhancement, and ripple reduction techniques were implemented.
• Circuit simulations were performed using a 0.18 μm CMOS technology, including Monte Carlo analysis for robustness.

Main Results:

• The designed chopper amplifier operates with 3.7 μA current from a ±0.6V supply.
• Achieved a bandwidth of 50 mHz to 10 kHz with an input-referred noise of 2.9 μVrms and a mid-band gain of 40 dB.
• Demonstrated tolerance to 60 mV DC electrode offset, an input impedance of 17 MΩ, and mean CMRR/PSRR of 94/80 dB after Monte Carlo analysis.

Conclusions:

• The proposed neural chopper amplifier is suitable for EEG, LFP, and AP signal recording due to its high CMRR, PSRR, and low noise figure.
• The optimized multi-stage design effectively minimizes noise and maximizes bandwidth while maintaining low power consumption.
• The amplifier's robustness against process variations and mismatches is confirmed through extensive simulations, validating its practical applicability.