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

A chopper instrumentation amplifier (IA) dedicated for bio-potential acquisition usually requires a linearized input stage for large electrode offset voltage accommodation. This linearization leads to excessive power consumption when sufficiently low input-referred noise (IRN) is required. We present a current-balance IA (CBIA) without the need for the input stage linearization. It uses two transistors to operate as an input transconductance stage and a dc-servo loop (DSL) at the same time. An off-chip capacitor completes the DSL by ac coupling the source terminals of the input transistors via chopping switches realizing a sub-Hz high-pass cutoff frequency for dc rejection. Fabricated in a 0.35-mu m CMOS process, the proposed CBIA occupies 0.41 mm(2) and consumes 1.19 mu W from a 3 V dc supply. Measurements show that the IA achieves an input-referred noise of 0.91 mu V-rms over 100 Hz bandwidth. This corresponds to a noise efficiency factor of 2.22. Typical CMRR of 102.1 dB is achieved for zero offset and degraded to 85.9 dB when a +/- 0.3 V input offset was applied. Gain variation of 0.5% is maintained within the range of +/- 0.4 V input offset. The resulting performance meets well with the requirement for ECG and EEG recording using dry electrodes. A demonstration for the use of the proposed IA on a human subject is also provided.

Automated summary

A current-balance instrumentation amplifier (CBIA) is proposed, which eliminates the need for input stage linearization and achieves low input-referred noise. This design uses two transistors to simultaneously operate as input transconductance stage and dc-servo loop (DSL), achieving sub-Hz high-pass cutoff frequency for dc rejection. The fabricated CBIA demonstrates good performance with an input-referred noise of 0.91 μV-rms over 100 Hz bandwidth.