A 300 mV DS Modulator Using a Gain Enhanced, Inverter Based Amplifier for Medical Implant Devices
An ultra low voltage low power switched capacitor (SC) delta sigma (DS) 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 mW of power.