US Patent 10097283 Watch-crystal-based RF transmitter

Example radio frequency (RF) transmitters and associated methods are disclosed. One example RF transmitter includes an RF oscillator, a real-time clock (RTC) oscillator. and a control circuit. The control circuit is configured to determine whether a calibration of the RF oscillator is needed; electrically couple the RF oscillator to the RTC oscillator and initiate calibrating of the RF oscillator using the RTC oscillator when it is determined that the calibration is needed; and activate the RF oscillator to operate in an open-loop mode to generate an RF signal for data transmission. The calibration can be performed in a closed-loop mode before the data transmission or in an open-loop mode during the data transmission.