Boosted-bias tunable filter with dynamic calibration

1. A signal communication device comprising:

a frequency-selective filter having at least one component that is biased by a control signal to establish a center frequency of the frequency-selective filter; and

a closed-loop bias generator to generate the control signal and to adjust the control signal based, at least in part, on a comparison of the control signal and a reference signal.

2. The signal communication device of claim 1 wherein the closed-loop bias generator comprises:

a bias control circuit to generate charge-enable pulses; and

a bias accumulator that accumulates charge in response to the charge-enable pulses, the accumulated charge establishing a voltage level of the control signal.

3. The signal communication device of claim 2 wherein the bias control circuit comprises:

a comparator to compare the reference signal and the control signal and to generate a pulse-enable signal in either a first state or a second state according to the comparison of the control signal and the reference signal; and

pulse control logic to output the charge-enable pulses to the bias accumulator when the pulse-enable signal is in the first state and to cease outputting the charge-enable pulses to the bias accumulator when the pulse-enable signal is in the second state.

4. The signal communication device of claim 1 wherein the at least one component is a varactor and wherein the control signal is a varactor bias voltage.

5. The signal communication device of claim 4 wherein the closed-loop bias generator is implemented in part within an integrated circuit device that is powered by a logic-level supply voltage, and in part by a set of discrete components that operate to generate a varactor bias voltage within a range of voltages that extends to a higher voltage than the logic-level supply voltage.

6. The signal communication device of claim 5 wherein the integrated circuit device comprises a signal receiver coupled to receive a filtered signal from the frequency-selective filter and to recover an information-bearing signal from the filtered signal.

7. The signal communication device of claim 5 wherein the integrated circuit device comprises a signal transmitter coupled to output a modulated carrier to the frequency-selective filter.

8. The signal communication device of claim 1 further comprising a digital-to-analog converter to generate the reference signal at a level indicated by a digital control word.

9. The signal communication device of claim 1 wherein the closed-loop bias generator comprises a bias control circuit to generate a sequence of charge-enable pulses with a duty cycle determined, at least in part, by a digital control word that indicates a desired level of the control signal.

10. The signal communication device of claim 1 wherein the closed-loop bias generator comprises a bias control circuit to generate a sequence of charge-enable pulses at a frequency determined, at least in part, by a digital control word that indicates a desired level of the control signal.

11. The signal communication device of claim 1 further comprising a calibration circuit to generate a sequence of digital control words that establish respective levels of the control signal and to determine which of the digital control words yields either a maximum or minimum output from the frequency-selective filter.

12. The signal communication device of claim 11 further comprising a plurality of storage elements, each to store a respective digital control word that yields a maximum or minimum output from the frequency-selective filter for a corresponding channel selection.

13. The signal communication device of claim 1 wherein the circuitry to generate the sequence of pulses comprises circuitry to generate the sequence of pulses with a duty cycle and a frequency determined, at least in part, by a selected one of the digital control words.

14. The signal communication device of claim 1 wherein the circuitry to generate the sequence of pulses comprises circuitry to generate the sequence of pulses with a duty cycle determined, at least in part, by a selected one of the digital control words.

15. The signal communication device of claim 1 wherein the circuitry to generate the sequence of pulses comprises circuitry to generate the sequence of pulses at a frequency determined, at least in part, by a selected one of the digital control words.

16. An integrated circuit device comprising:

a calibration circuit coupled to receive a band-limited signal from an external filter network and to determine digital control words that yield maximum or minimum levels of the band-limited signal for respective frequency bands within a broader frequency spectrum; and

a bias control circuit to generate a control signal for controlling a center frequency of the external filter network within a selected one of the frequency bands based, at least in part, on the respective one of the digital control words, the bias control circuit including circuitry to generate a sequence of pulses that may be applied within an external bias accumulator circuit to develop a bias voltage for controlling the center frequency of the external filter network.

17. The integrated circuit device of claim 16 wherein the calibration circuit comprises circuitry to generate, for each of the frequency bands, a sequence of digital control words and to compare levels of the band-limited signal that result for each digital control word of the sequence of digital control words.

18. A method of tuning a frequency-selective filter having a center frequency that is established by a control signal, the method comprising:

generating a reference signal that corresponds to a desired center frequency;

comparing the control signal with the reference signal to generate a comparison result; and

adjusting the control signal according to the comparison result.

19. The method of claim 18 wherein generating a reference signal that corresponds to the desired center frequency comprises converting a digital control word into an analog reference signal.

20. The method of claim 18 wherein generating a reference signal that corresponds to the desired center frequency comprises generating a sequence of reference signals having respective signal levels to determine which of the sequence of reference signals yields either a maximum or minimum output from the frequency-selective filter.

21. An integrated circuit device comprising:

means for receiving a band-limited signal from an external filter network and for determining digital control words that yield maximum or minimum levels of the band-limited signal for respective frequency bands within a broader frequency spectrum; and

means for generating a control signal for controlling a center frequency of the external filter network within a selected one of the frequency bands based, at least in part, on the respective one of the digital control words.

22. Computer-readable media, the computer-readable media having information embodied therein that includes a description of an integrated circuit device, the information including descriptions of:

a calibration circuit coupled to receive a band-limited signal from an external filter network and to determine digital control words that yield maximum or minimum levels of the band-limited signal for respective frequency bands within a broader frequency spectrum; and

a bias control circuit to generate a control signal for controlling a center frequency of the external filter network within a selected one of the frequency bands based, at least in part, on the respective one of the digital control words, the bias control circuit including circuitry to generate a sequence of pulses that may be applied within an external bias accumulator circuit to develop a bias voltage for controlling the center frequency of the external filter network.