Low-power sensing and digitization of cardiac signals based on sigma-delta conversion

In this work we propose an architecture for the acquisition and digitization of cardiac signals in a pacemaker, based on ΣΔ modulation. Due to the characteristics of such an application, the proposed system presents the typical design challenges of low-voltage, low-power circuits. The work demonstrates that, thanks to the narrow bandwidth typical of biological signals (50-150 Hz), oversampling conversion techniques can be advantageous in terms of power dissipation at a given dynamic range. The converter is designed in a 0.8 μm CMOS technology using the switched op-amp technique. The ΣΔ converter is a third order modulator with an oversampled frequency of about 8 kHz and the circuit can operate at a minimum supply voltage of 2 V, while dissipating 2 μW at most. According to simulation results the dynamic range is larger than 50 dB.