Phase-locked loop modulation

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 different from the first frequency and first phase,
• the first division control signal being generated independently of the oscillating output signal such that, when the phase-locked loop is operating in the second mode, the first division control signal remains operative to produce the same phase as when the phase-locked loop is operating in the first mode.