Phase Locked Loop-Based Tuning Adjustable Filter

A method comprising:

• detecting a phase difference between a test signal input into a circuit and a signal output by the circuit, the circuit including an amplifier and an adjustable filter;
• generating a phase difference signal that indicates the phase difference between a center frequency of the test signal input into the circuit and a center frequency of the signal output by the circuit;
• processing the phase difference signal to provide a tuning signal;
• and
• setting an adjustable characteristic of the adjustable filter using the tuning signal.

A method comprising:

• providing an oscillation signal from a local oscillator to a first circuit and to a parallel coupled second circuit, the first circuit including an adjustable filter;
• detecting a phase difference between a first output oscillation signal from the first circuit and a second output oscillation signal from the second circuit;
• generating a phase difference signal indicating the phase difference between the first output oscillation signal and the second output oscillation signal;
• filtering the phase difference signal using a low pass filter to generate a tuning signal having an adjustment value corresponding to the phase difference between the first output oscillation signal and the second output oscillation signal;
• and
• setting the adjustable filter based on the adjustment value of the tuning signal.

A system comprising:

• a first circuit including an amplifier and an adjustable filter, the first circuit configured to receive an oscillator signal;
• a second circuit coupled in parallel with the first circuit to receive the oscillator signal, the second circuit including an amplifier and a fixed value filter;
• and
• an adjustment circuit including a phase detector to detect a phase difference between an output oscillation signal from the first circuit and an output oscillation signal from the second circuit, the adjustment circuit configured as a phase locked loop (PLL) to generate a tuning signal to set an adjustment value of the first circuit based on the detected phase difference and to lock the center frequency of the first circuit to the frequency of the oscillator signal.