High precision biomedical sensor readout circuits design for wearable health monitoring system

Abstract

This chapter presents a new low-jitter low-power RC relaxation oscillator for biomedical sensor interface application. A novel switch-capacitor based energy efficient swing boosting RC network is proposed to effectively improve the oscillator phase noise and energy efficiency. A low input-referred noise low power inverter-based comparator with replica biasing is employed to enhance the phase noise performance and to reduce output frequency inaccuracy over supply voltage variation. A first-order temperature compensated timing resistor is designed to reduce the output frequency inaccuracy over temperature variations. The prototype relaxation oscillator circuit is designed and fabricated in a commercial 65 nm CMOS process. The measured output frequency is 3 MHz under nominal supply voltage of 1 V, consuming a total power of 17.3 µW. This design achieves an energy efficiency of 5.7 pJ/cycle, and output phase noise of -114 dBc/Hz at 100 kHz offset frequency. The measured relative period jitter is 0.015%. The frequency inaccuracy is ±0.15% over a supply range of 1 V to 1.6 V, and ±0.6% over a temperature range of 0°C to 90°C. The Figure -of-Merit (FOM) is computed to be 161 dBc/Hz, which compares favorably with the benchmark FOM of 162.1 dBc/Hz [42].