Bi-quad calibration
Embodiments include methods of tuning state variable filters. Examples include state variable filters whose center frequencies can be tuned using variable gain blocks coupled to outputs of filter integrators. First- and second-order state variable filters may operate on signals in parallel and their outputs combined to produce a filtered output. Filters may be tuned to pass or reject signals depending on the application; sample applications include, but are not limited to: agile filtering; spectrum analysis; interference detection and rejection; equalization; direct intermediate-frequency transmission; and single-sideband modulation and demodulation.
1. A method of tuning a filter of a biquad circuit, the biquad circuit comprising analog circuit components including a loss pad, a first integrator, and a second integrator, the method comprising:
tuning the loss pad to generate a target gain value at a predetermined frequency;
tuning a phase of the first integrator to a target phase at the predetermined frequency;
tuning a phase of the second integrator to the target phase at the predetermined frequency; and
tuning a gain of the first integrator to the target gain value at the predetermined frequency; and
tuning a gain of the second integrator to the target gain value at the predetermined frequency;
wherein each tuning step comprises changing circuit values.
2. The method of claim 1 , further comprising determining the target gain value at the predetermined frequency.
3. The method of claim 1 , wherein tuning the loss pad includes adjusting an attenuation value at the loss pad.
4. The method of claim 1 , wherein tuning the phase of the first integrator includes adjusting a phase value of an input at the first integrator, the phase value controlling the phase of the first integrator.
5. The method of claim 1 , wherein tuning the gain of the first integrator includes adjusting a coarse gain value and adjusting a fine gain value at the first integrator, the coarse gain value and fine gain value controlling the gain of the first integrator.
6. The method of claim 1 , wherein tuning the phase of the second integrator includes adjusting a phase value of an input at the second integrator, the phase value controlling the phase of the second integrator.
7. The method of claim 1 , wherein tuning the gain of the second integrator includes adjusting a coarse gain value and adjusting a fine gain value at the second integrator, the course gain value and fine gain value controlling the gain of the second integrator.
8. The method of claim 1 , wherein the biquad circuit is tuned to operate as a notch filter.
9. The method of claim 1 , wherein the biquad circuit is tuned to operate as an all-pass filter.