CMOS RF Transmitter Using Pulsewidth Modulation for Wireless Smart Sensors

This paper presents the radio frequency (RF) transmitter using pulsewidth modulation (PWM) method. The proposed transmitter can perform with lower power consumption compared to other RF transmitters using a conventional ring oscillator because the proposed voltage-controlled oscillator (VCO) is operated by ON-/OFF-time of the PWM signal. Moreover, the proposed VCO with a metal-oxide semiconductor switch can reduce the power consumption significantly due to the reduction of idle current loss. The power dissipation of the transmitter is measured as 0.75 mW at a carrier of 315 MHz. The transmission of the modulated signal is performed by the on-chip antenna with bond-wire inductor. The on-chip antenna has gain of -34.33 dBi. The radiated power is measured as -32.3 dBm at a distance of 10 cm between the receiver and the transmitter.