Method and apparatus for automatic center frequency tuning of tunable bandpass filters

DETAILED DESCRIPTION A radio having a tunable bandpass filter wherein the filter is tuned by apparatus within the radio is disclosed.
The apparatus comprises a reference generator for generating a reference signal to tune the tunable bandpass filter to a desired center frequency.
The tunable bandpass filter receives the reference signal and provides a filter output signal.
A digital signal processing and control processor is connected to the tunable bandpass filter to receive the filter output signal.
The digital signal processing and control processor provides a phase error metric from the filter output signal and tunes the tunable bandpass filter to provide a desired phase error metric signal thereby tuning the tunable bandpass filter to the desired center frequency.
The digital signal processing and control processor further comprises a phase comparison function that provides the phase error metric from the filter output signal.
The phase comparison function comprises a low-frequency quadrature down converter tuned to a frequency below the desired center frequency to down convert the filter output signal into low-frequency in-phase and quadrature outputs.
A high-frequency quadrature down converter is tuned to a frequency above the desired center frequency to down convert the filter output signal into high-frequency in-phase and quadrature outputs.
In the phase comparison function a low-frequency phase measurement block is connected to the low-frequency quadrature down converter to provide a low-frequency phase angle from the low-frequency in-phase and quadrature outputs.
A high-frequency phase measurement block is connected to the high-frequency quadrature down converter to provide a high-frequency phase angle from the high-frequency in-phase and quadrature outputs.
A summing circuit compares the low-frequency phase angle and the high-frequency phase angle to provide a difference angle.
An absolute value function removes a negative sign from the difference angle.
An integrate and dump circuit integrates and dumps the difference angle value thereby providing the phase error metric