Efficient Low-Power Microwave Readout Circuit in 180 nm CMOS for Wearable Electronics

The integration of microwave sensors and CMOS technology contributes to the development of wearable electronics to support small form factor and low power devices. This paper presents a unique microwave readout integrated circuit incorporated with a split ring resonator (SRR), particularly designed for gas monitoring in wearable electronics. The readout circuit is composed of a cross-coupled LC oscillator and an RF-to-DC converter. The LC oscillator naturally excites the SRR at the sensor's operating frequency, eliminating the need for the bulky vector network analyzer. The RF output of the SRR is regulated to a measured DC voltage level using the RF-to-DC converter. This DC voltage can then be used to power up the ADC or digital block in the wearable electronic device. The monolithic microwave readout circuit has been designed, simulated and implemented in TSMC 180 nm CMOS, occupying an active area of 0.108 mm² and consuming a low power of 777.1 µW obtained from post-layout simulation at a supply voltage of 1.5 V. These characteristics make the microwave readout circuit suitable for integration in wearable electronics.