A Micropower Chopper CBIA Using DSL-Embedded Input Stage With 0.4 V EO Tolerance for Dry-Electrode Biopotential...

Area of Science:

• Electronics
• Biomedical Engineering
• Instrumentation

Background:

• Bio-potential acquisition systems require instrumentation amplifiers (IAs) with linearized input stages to handle large electrode offset voltages.
• Linearization often leads to high power consumption, especially when low input-referred noise (IRN) is critical.
• Existing solutions face trade-offs between power, noise, and offset voltage accommodation.

Purpose of the Study:

• To present a current-balance instrumentation amplifier (CBIA) that eliminates the need for input stage linearization.
• To achieve low power consumption while maintaining low input-referred noise (IRN) for bio-potential acquisition.
• To demonstrate the suitability of the CBIA for applications like ECG and EEG recording, particularly with dry electrodes.

Main Methods:

• A novel current-balance IA (CBIA) design utilizing two transistors as both input transconductance stage and DC-servo loop (DSL).
• Integration of an off-chip capacitor to complete the DSL, enabling sub-Hz high-pass cutoff via chopping switches for DC rejection.
• Fabrication in a 0.35-μm CMOS process, measuring key performance metrics including IRN, noise efficiency factor, CMRR, and gain variation.

Main Results:

• The CBIA achieves an input-referred noise (IRN) of 0.91 μVrms over a 100 Hz bandwidth with a noise efficiency factor of 2.22.
• Demonstrates typical common-mode rejection ratio (CMRR) of 102.1 dB, degrading to 85.9 dB with a ±0.3 V input offset.
• Maintains a gain variation of only 0.5% within a ±0.4 V input offset range, consuming 1.19 μW from a 3 V supply.

Conclusions:

• The proposed current-balance IA (CBIA) effectively accommodates large electrode offset voltages without input stage linearization.
• The design offers a significant reduction in power consumption (1.19 μW) while achieving excellent low noise performance (0.91 μVrms) and high CMRR.
• The CBIA's performance is well-suited for demanding bio-potential acquisition applications, including ECG and EEG recording with dry electrodes.