A 590-nA Fully-Integrated AFE Including a CSCCIA with SC Ripple Rejection and a Configurable SC-BPF for Implantable Cardiac Pacemakers

This paper presents a fully integrated analog frontend (AFE) circuit for implantable cardiac pacemakers, which consists of a chopper stabilization capacitively-coupled instrumentation amplifier (CS-CCIA) and a configurable $2^{\text {nd }}-$ order switched-capacitor bandpass filter (SC-BPF). To reduce the CCIA’s power consumption, the ripple induced by chopper is suppressed by a SC-resistor based circuit instead of conventional amplifier-based ripple rejection loop (RRL). The SC-BPF following the CS-CCIA provides 2 passband modes to extract 2 kinds of intracardiac electrocardiographs (iECG), such as the natural ECG and paced ECG. The SC scheme not only realizes fully integration of the BPF with passband lower than 200 Hz but also provides accurate frequency responses against PVT variations. Fabricated in a $180-\mathrm{nm}$ CMOS process, the AFE consumes only $\mathbf{5 9 0} \mathbf{n A}$ from a $\mathbf{2 - V}$ battery with $\mathbf{8 - k H z}$ clock for the SC circuits. The 2 configurable passbands are $12 \sim 188 \mathrm{~Hz}$ and $38 \sim 97 \mathrm{~Hz}$ with $35.5-\mathrm{dB}$ and $39.4-\mathrm{dB}$ passband gain. The fully integrated AFE’s input reference noise is $\mathbf{2. 7 5}$ $\mu \mathrm{V}_{\text {rms }}$ and $1.79 \mu \mathrm{~V}_{\text {rms }}$ in the two modes, respectively, while occupying $0.44-\mathrm{mm}^{2}$ active area.