A 300-mV ΔƩ modulator using a gain-enhanced, inverter-based amplifier for medical implant devices

Abstract

An ultra-low-voltage low-power switched-capacitor (SC) delta-sigma (ΔΣ) modulator running at a supply voltage as low as 300 mV is presented for biomedical implant devices, e.g., cardiac pacemakers. To reduce the supply voltage, an inverter-based amplifier is used in the integrators, whose DC gain and gain-bandwidth (GBW) are boosted by a simple current-mirror output stage. The full input-feedforward loop topology offers low integrators internal swing, supporting ultra-low-voltage operation. To demonstrate the concept, a second-order loop topology was chosen. The entire modulator operates reliably against process, voltage and temperature (PVT) variations from a 300 mV ± 10% supply voltage only, while the switches are driven by a charge pump clock boosting scheme. Designed in a 65 nm CMOS technology and clocked at 256 kHz, the simulation results show that the modulator can achieve a 64.4 dB signal-to-noise ratio (SNR) and a 60.7 dB signal-to-noise and distortion ratio (SNDR) over a 1.0 kHz signal bandwidth while consuming 0.85 µW of power.