An FSK modulator at 23.2 MHz with ±0.9% accuracy for the USB power delivery standard

This paper presents an FSK modulator suitable for a transmitter chain within the new USB Power Delivery standard. The proposed solution performs a binary FSK modulation using a relaxation voltage-controlled oscillator with a voltage averaging feedback. A reference proportional to supply is used to compensate real-time frequency variations, whereas the frequency spread due to the process is corrected by an 8 bit trimming system. The considered input signal bit rate is 300 kbps and the carrier frequency is 23.2 MHz with ±0.5 MHz frequency deviation. The proposed modulator grants ±0.9% accuracy against PVT spread by consuming 1.2 mW and phase noise at 20kHz from the carrier lower than -56 dBc/Hz.