A 2.4 GHz CMOS Pulse-Mode Transmitter for RF Body-Contouring Device Applications

Body-contouring devices deliver controlled thermal energy to treat cellulite, reduce localized fat, and improve skin elasticity. Since the thermal effect is closely related to the delivered RF output power, precise control of the output power is critical for both efficacy and safety. In this study, we propose a 2.4 GHz CMOS pulse-mode transmitter for body-contouring device applications, featuring precise control of the average power delivered to the body. The transmitter comprises a fully integrated phase-locked loop (PLL) synthesizer, pulse modulator (PM), and 10 mW power amplifier (PA). It is fabricated in a 65 nm CMOS with a compact die area of 3.75 mm2. The PA provides four-level continuous-mode output control from −0.3 dBm to 11.1 dBm, and the PM performs programmable PA switching for pulse-mode operation of the PA with a wide range of pulse rates and duty ratios. By combining the continuous-mode output power control and pulse-mode on–off time regulation, the average output power delivered to the skin is finely controlled, managing the delivered power within a safe skin temperature below 65 °C. The PLL loop filter is fully integrated with a wide programmability, improving the form factor and bill of materials for the target devices. Measurement results confirm that the designed transmitter can accurately control both the average output power and pulse profile across the 2.4 GHz ISM band, demonstrating its suitability for compact home-use RF body-contouring devices.