CMOS Monolithic Thermostatic Microwave Heater With Bioimpedance Load Effect Compensation

Abstract

Based on microwave heating, a monolithic low-power temperature-programmable high-precision microheater is implemented for thermotherapy. The microwave heater is designed and fabricated in 0.18- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> CMOS process. The <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula> -factor of the on-chip inductor that serves as the heat applicator would be degraded by the bioimpedance load effect when the heating target is in the vicinity of the microwave heater. Because of such bioimpedance load effect, the electric field around the heat applicator is decreased, which limits the heating efficiency of the microwave heater. To improve the heating efficiency, a bioimpedance load effect compensation technique is adopted to enhance the electric field around the heat applicator. Moreover, a time-to-digital converter (TDC)-based temperature sensor with a sensing resolution of 0.052 is employed to realize the thermostatic function with the precision of ±0.1 °C. Consuming 136 mW, the power amplifier of the heater delivers the output power of 25.36 mW (14 dBm). The heating rate of 0.24 °C/min and heating efficiency of 34.4 J/°C are achieved.