System and method for transitioning from one PLL feedback source to another

• Main Authors: ORTIZ JEFFERY PETER, HUMPHREYS SCOTT ROBERT, HIETALA ALEXANDER WAYNE
• Format: Patent
• Language: English
• Published: 12.08.2008
• Subjects: AUTOMATIC CONTROL, STARTING, SYNCHRONISATION, OR STABILISATIONOF GENERATORS OF ELECTRONIC OSCILLATIONS OR PULSES; BASIC ELECTRONIC CIRCUITRY; ELECTRIC COMMUNICATION TECHNIQUE; ELECTRICITY; TRANSMISSION

A system and method are provided for switching from one phase-locked loop feedback source to another in a radio frequency (RF) transmitter. The RF transmitter includes a phase-locked loop (PLL) that provides a phase-modulated RF input signal and power amplifier circuitry that amplifies the RF input signal to provide an RF output signal. The PLL includes switching circuitry that couples a feedback path of the PLL to an output of the PLL for open loop operation and couples the feedback path of the PLL to an output of the power amplifier circuitry for closed loop operation. Prior to switching the feedback path from the output of the PLL to the output of the power amplifier circuitry, time alignment circuitry operates to time-align feedback signals from the outputs of the PLL and the power amplifier circuitry such that switching from open loop operation to closed loop operation causes minimal phase disturbance.