Power efficient crest factor reduction

1. A circuit comprising:

crest factor reduction (CFR) circuitry including:

a peak neighborhood analyzer having a first terminal and a second terminal;

peak detection circuitry having a first terminal, a second terminal, and a third terminal; and

a controller having a first terminal and a second terminal, the first terminal of the controller coupled to the second terminal of the peak neighborhood analyzer, the second terminal of the controller coupled to the second terminal of the peak detection circuitry,

wherein the peak neighborhood analyzer is configured to:

receive an input signal at the first terminal of the peak neighborhood analyzer;

analyze the input signal to determine whether a peak larger than a target threshold is expected within an interval; and

provide a first control signal at the second terminal of the peak neighborhood analyzer responsive to determining that a peak larger than the target threshold is expected within the interval, and

wherein the controller is configured to:

receive the first control signal at the first terminal of the controller; and

gate a clock or data to the peak detection circuitry responsive to the first control signal.

2. The circuit of claim 1 , wherein the peak neighborhood analyzer includes envelope calculation circuitry and peak absence prediction circuitry, the envelope calculation circuitry having a first terminal and a second terminal, the peak absence prediction circuitry having a first terminal and a second terminal, the first terminal of the envelope calculation circuitry coupled to the first terminal of the peak neighborhood analyzer, the second terminal of the envelope calculation circuitry coupled to the first terminal of the peak absence prediction circuitry, the second terminal of the peak absence prediction circuitry coupled to the second terminal of the peak neighborhood analyzer.

3. The circuit of claim 2 , wherein the envelope calculation circuitry is configured to:

receive input signal samples at the first terminal of the envelope calculation circuitry, the input signal samples associated with a baseband interface rate;

calculate envelope values of the input signal samples; and

provide the envelope values at the second terminal of the envelope calculation circuitry.

4. The circuit of claim 3 , wherein the peak absence prediction circuitry is configured to:

receive the envelope values at the first terminal of the peak absence prediction circuitry;

compare the envelope values to the target threshold to obtain comparison results; and

provide the first control signal responsive to the comparison results indicating the envelope values stay below the target threshold for at least a threshold number of input signal samples.

5. The circuit of claim 1 , wherein the controller has a third terminal, the CFR circuitry includes interpolated envelope calculation circuitry having a first terminal, a second terminal, and a third terminal, the second terminal of the interpolated envelope calculation circuitry coupled to the third terminal of the controller, the third terminal of the interpolated envelope calculation circuitry coupled to the first terminal of the peak detection circuitry, and the controller is configured to:

receive the first control signal at the first terminal of the controller; and

gate a clock or data to the interpolated envelope calculation circuitry responsive to the first control signal.

6. The circuit of claim 5 , wherein the controller has a fourth terminal, the CFR circuitry includes interpolation circuitry having a first terminal, a second terminal, and a third terminal, the second terminal of the interpolation circuitry coupled to the fourth terminal of the controller, the third terminal of the interpolation circuitry coupled to the first terminal of the interpolated envelope calculation circuitry, and the controller is configured to:

receive the first control signal at the first terminal of the controller; and

gate a clock or data to the interpolation circuitry responsive to the first control signal.

7. The circuit of claim 6 , wherein the fourth terminal of the controller is one terminal of a set of fourth terminals of the controller, the interpolation circuitry includes a set of poly-phase filters, each poly-phase filter of the set of poly-phase filters having a first terminal, a second terminal, and a third terminal, each second terminal of each respective poly-phase filter coupled to a respective terminal of the set of fourth terminals, and the controller is configured to:

receive the first control signal at the first terminal of the controller; and

gate a clock or data to each poly-phase filter of the set of poly-phase filters responsive to the first control signal.

8. The circuit of claim 1 , wherein the CFR circuitry includes peak cancellation circuitry having a first terminal, a second terminal, and a third terminal, the first terminal of the peak cancellation circuitry is coupled to the third terminal of the peak detection circuitry, the peak detection circuitry is configured to detect when a peak of the input signal is greater than a peak limit, the peak limit greater than the target threshold, and the peak cancellation circuitry is configured to:

calculate an excess peak portion of the detected peak relative to the peak limit; and

apply a correction to the detected peak based on the excess peak portion.

9. The circuit of claim 1 , wherein the CFR circuitry includes peak cancellation circuitry having a first terminal, a second terminal, and a third terminal, the first terminal of the peak cancellation circuitry coupled to the third terminal of the peak detection circuitry, the second terminal of the peak cancellation circuitry coupled to the first terminal of the peak neighborhood analyzer, and the peak cancellation circuitry including:

envelope calculation circuitry having a first terminal and a second terminal, the first terminal of the envelope calculation circuitry coupled to the first terminal of the peak cancellation circuitry;

excess peak calculation circuitry having a first terminal and a second terminal, the first terminal of the excess peak calculation circuitry coupled to the second terminal of the envelope calculation circuitry;

a delay line having a first terminal and a second terminal, the first terminal of the delay line coupled to the first terminal of the peak cancellation circuitry; and

a multiplier having a first terminal, a second terminal, and a third terminal, the first terminal of the multiplier coupled to the second terminal of the delay line, the second terminal of the multiplier coupled to the second terminal of the excess peak calculation circuitry.

10. The circuit of claim 9 , wherein the peak cancellation circuitry includes:

cancellation pulse generation circuitry having a first terminal and a second terminal, the first terminal of the cancellation pulse generation circuitry coupled to the third terminal of the multiplier;

delay circuitry having a first terminal and a second terminal, the first terminal of the delay circuitry coupled to the second terminal of the peak cancellation circuitry; and

combine circuitry having a first terminal, a second terminal, and a third terminal, the first terminal of the combine circuitry coupled to the second terminal of the cancellation pulse generation circuitry, the second terminal of the combine circuitry coupled to the second terminal of the delay circuitry, and the third terminal of the combine circuitry coupled to the third terminal of the peak cancellation circuitry.

11. A transmitter comprising:

crest factor reduction (CFR) circuitry including:

peak detection circuitry having a first terminal, a second terminal, and a third terminal; and

peak cancellation circuitry having a first terminal, a second terminal, and a third terminal, the first terminal of the peak cancellation circuitry coupled to the third terminal of the peak detection circuitry, the peak cancellation circuitry including:

envelope calculation circuitry having a first terminal and a second terminal, the first terminal of the envelope calculation circuitry coupled to the first terminal of the peak cancellation circuitry;

excess peak calculation circuitry having a first terminal and a second terminal, the first terminal of the excess peak calculation circuitry coupled to the second terminal of the envelope calculation circuitry;

a delay line having a first terminal and a second terminal, the first terminal of the delay line coupled to the first terminal of the peak cancellation circuitry; and

a multiplier having a first terminal, a second terminal, and a third terminal, the first terminal of the multiplier coupled to the second terminal of the delay line, the second terminal of the multiplier coupled to the second terminal of the excess peak calculation circuitry.

12. The transmitter of claim 11 , wherein the peak cancellation circuitry includes:

cancellation pulse generation circuitry having a first terminal and a second terminal, the first terminal of the cancellation pulse generation circuitry coupled to the third terminal of the multiplier;

delay circuitry having a first terminal and a second terminal, the first terminal of the delay circuitry coupled to the second terminal of the peak cancellation circuitry; and

combine circuitry having a first terminal, a second terminal, and a third terminal, the first terminal of the combine circuitry coupled to the second terminal of the cancellation pulse generation circuitry, the second terminal of the combine circuitry coupled to the second terminal of the delay circuitry, and the third terminal of the combine circuitry coupled to the third terminal of the peak cancellation circuitry.

13. The transmitter of claim 11 , wherein the CFR circuitry includes:

a peak neighborhood analyzer having a first terminal and a second terminal; and

a controller having a first terminal and a second terminal, the first terminal of the controller coupled to the second terminal of the peak neighborhood analyzer, the second terminal of the controller coupled to the second terminal of the peak detection circuitry, the peak neighborhood analyzer configured to:

receive input signal samples at the first terminal of the peak neighborhood analyzer;

analyze the input signal samples to determine whether a peak larger than a target threshold is expected within an interval; and

provide a control signal at the second terminal of the peak neighborhood analyzer responsive to determining that a peak larger than the target threshold is not expected within the interval.

14. The transmitter of claim 13 , wherein the peak neighborhood analyzer includes envelope calculation circuitry and peak absence prediction circuitry, the envelope calculation circuitry having a first terminal and second terminal, the peak absence prediction circuitry having a first terminal and a second terminal, the first terminal of the envelope calculation circuitry coupled to the first terminal of the peak neighborhood analyzer, the second terminal of the envelope calculation circuitry coupled to the first terminal of the peak absence prediction circuitry, the second terminal of the peak absence prediction circuitry coupled to the second terminal of the peak neighborhood analyzer, the envelope calculation circuitry configured to calculate envelope values of the input signal samples, and the peak absence prediction circuitry configured to:

receive the envelope values at the first terminal of the peak absence prediction circuitry;

compare the envelope values to the target threshold to obtain comparison results; and

provide the control signal at the first terminal of the peak absence prediction circuitry responsive to the comparison results indicating the envelope values stay below the target threshold for at least a threshold number of input signal samples.

15. The transmitter of claim 13 , wherein the controller has a third terminal, the CFR circuit further comprises interpolated envelope calculation circuitry having a first terminal, a second terminal, and a third terminal, the second terminal of the interpolated envelope calculation circuitry coupled to the third terminal of the controller, the third terminal of the interpolated envelope calculation circuitry coupled to the first terminal of the peak detection circuitry, and the controller is configured to:

receive the control signal at the first terminal of the controller; and

gate a clock or data to the interpolated envelope calculation circuitry responsive to the control signal.

16. The transmitter of claim 15 , wherein the controller has a fourth terminal, the CFR circuitry includes interpolation circuitry having a first terminal, a second terminal, and a third terminal, the second terminal of the interpolation circuitry coupled to the fourth terminal of the controller, the third terminal of the interpolation circuitry coupled to the first terminal of the interpolated envelope calculation circuitry, and the controller is configured to:

receive the control signal at the first terminal of the controller; and

gate a clock or data to the interpolation circuitry responsive to the control signal.

17. A method comprising:

receiving a transmit signal;

selectively enabling peak detection based on a peak absence prediction for the transmit signal;

when enabled, performing peak detection by comparing a peak of the transmit signal to a peak limit;

calculating an excess peak portion of the peak relative to the peak limit;

applying a correction to the peak based on the excess peak portion; and

providing an updated transmit signal with the corrected peak.

18. The method of claim 17 , wherein calculating the excess peak portion includes:

calculating an envelope value for an interpolated transmit signal sample;

comparing the envelope value to the peak limit to obtain comparison results; and

determine the excess peak portion based on the comparison results.

19. The method of claim 17 , wherein performing peak absence detection includes:

receiving transmit signal samples for an interval of the transmit signal;

calculating envelope values for the transmit signal samples;

comparing the envelope values to a threshold to obtain comparison results, the threshold less than the peak limit; and

in response to the comparison results indicating there is no peak larger than the threshold within the interval, providing a control signal, and

the method further comprises disabling peak detection circuitry used to perform the peak detection responsive to the control signal.

20. The method of claim 19 , further comprising disabling interpolated envelope calculation circuitry used to provide envelope values to the peak detection circuitry responsive to the control signal.