A phase-locked loop having: an oscillator for forming an oscillating output signal; a frequency divider connected to receive the output of the oscillator and frequency divide it by a value dependent on a division control signal; and a phase comparator for comparing the phase of the divided signal and a reference signal to generate a control signal, the operation of the oscillator being dependent on the control signal; a first mode of operation in which the frequency divider is configured to operate in dependence on a first division control signal such that the resultant oscillating output signal has a first frequency and first phase, a second mode of operation in which the frequency divider is configured to operate in dependence on a second division control signal such that the resultant oscillating output signal has a second frequency and second phase, the first division control signal being generated independently of the oscillating output signal such that the first phase is maintained when the phase-locked loop is operating in a second mode.