Phase locked loop and method for trimming a loop filter

A phase locked loop, comprising:

• a voltage-controlled oscillator comprising a setting input and with a signal output that forms a control loop output from the phase locked loop;
• a phase comparator comprising a reference input configured to receive a reference signal, a feedback input connected to the signal output of the voltage-controlled oscillator via a frequency divider to form a feedback path, and an output, and configured to output an actuating signal at the output thereof based on a comparison of a feedback path signal and the reference signal;
• a charge pump configured to output a control voltage derived from the actuating signal, the charge pump comprising a control input connected to the output of the phase comparator;
• a loop filter comprising an output coupled to the setting input of the voltage-controlled oscillator and an input configured to receive the control voltage from the charge pump, and comprising a first charge store and at least one tunable element configured to selectively alter a filter characteristic of the loop filter;
• and
• a means for determining an initial loop filter characteristic of the loop filter and comparing the initial filter characteristic to a reference characteristic, and altering the initial filter characteristic to an adjusted filter characteristic based on the comparison.

A method for trimming a loop filter in a phase locked loop, comprising:

• providing a loop filter comprising at least one charge store and having an initial filter characteristic;
• supplying a charging current to the loop filter;
• determining a time period required to charge the at least one charge store;
• and
• altering the filter characteristic of the loop filter based on the determined time period.