Apparatus and method for crest factor reduction architecture
A device and a method for crest factor reduction reduces peak-to-average ratio (PAR) to increase power amplifier efficiency. A first hard clipping block performs hard clipping on an input signal when the amplitude of the input signal is greater than a first threshold. A shaping filter reshapes the spectrum of the hard clipped signal. An interpolator increases the sampling rate of the reshaped signal. A second hard clipping block performs hard clipping on the interpolated signal when the amplitude of the interpolated signal is greater than a second threshold.
1. For use in a crest factor reduction architecture, a device comprising:
a first hard clipping block configured to hard clip an input signal when the amplitude of the input signal is greater than a first threshold and output a clipped signal;
a shaping filter configured to reshape a spectrum of the clipped signal toward a spectrum shape of the input signal, and output the reshaped signal;
an interpolator configured to increase a sampling rate of the reshaped signal and output an interpolated signal; and
a second hard clipping block configured to hard clip the interpolated signal when the amplitude of the interpolated signal is greater than a second threshold and output an output signal.
2. The device of claim 1 , wherein the first threshold is lower than the second threshold.
3. The device of claim 1 , wherein the shaping filter is further configured to reshape the spectrum of the clipped signal by causing a mild re-growth of one or more peaks of the input signal that were clipped by the first hard clipping block.
4. The device of claim 3 , wherein the first threshold is determined based on at least one of a resulting adjacent channel leakage ratio (ACLR) and an error vector magnitude (EVM), wherein the shaping filter is configured to restore the resulting ACLR close to an initial ACLR of the input signal.
5. The device of claim 1 , wherein the interpolator is a first interpolator, the device further comprising a second interpolator configured to increase the sampling rate of the output signal.
6. The device of claim 1 , wherein the interpolator comprises at least a first stage interpolator and a second stage interpolator, the first stage interpolator configured to output a first stage signal.
7. The device of claim 6 , further comprising a third hard clipping block located between the first stage interpolator and the second stage interpolator, the third hard clipping block configured to hard clip the first stage signal when the amplitude of the first stage signal is greater than a third threshold.
8. The device of claim 1 , further comprising a window clipping block configured to window clip the output signal, wherein a window clipping threshold determines the peak-to-average ratio (PAR) of the output signal.
9. A method for crest factor reduction, the method comprising:
hard clipping an input signal when the amplitude of the input signal is greater than a first threshold to output a clipped signal;
reshaping a spectrum of the clipped signal toward a spectrum shape of the input signal, and outputting the reshaped signal;
increasing a sampling rate of the reshaped signal to output an interpolated signal; and
hard clipping the interpolated signal when the amplitude of the interpolated signal is greater than a second threshold to output an output signal.
10. The method of claim 9 , wherein the first threshold is lower than the second threshold.
11. The method of claim 9 , wherein reshaping the spectrum of the clipped signal comprises causing a mild re-growth of one or more peaks of the input signal that were clipped by the first hard clipping.
12. The method of claim 11 , wherein the first threshold is determined based on at least one of a resulting adjacent channel leakage ratio (ACLR) and an error vector magnitude (EVM), such that reshaping the clipped signal increases the resulting ACLR close to an initial ACLR of the input signal.
13. The method of claim 9 , further comprising increasing the sampling rate of the output signal.
14. The method of claim 9 , wherein increasing the sampling rate of the clipped signal comprises performing a first stage interpolation and a second stage interpolation, and wherein the first stage interpolation outputs a first stage signal.
15. The method of claim 14 , further comprising hard clipping the first stage signal when the amplitude of the first stage signal is greater than a third threshold.
16. The method of claim 9 , further comprising window clipping the output signal, wherein the window clipping threshold determines the peak-to-average ratio (PAR) of the output signal.
17. A transmitter, comprising:
a crest factor reduction device configured to:
perform a first hard clip on an input signal when the amplitude of the input signal is greater than a first threshold,
reshape a spectrum of the first hard clipped signal toward a spectrum shape of the input signal,
interpolate the reshaped signal to increase a sampling rate of the reshaped signal, and
perform a second hard clip on the interpolated signal when the amplitude of the interpolated signal is greater than a second threshold.
18. The transmitter of claim 17 , wherein the first threshold is lower than the second threshold.
19. The transmitter of claim 17 , wherein the crest factor reduction device is a field-programmable gate array (FPGA).
20. The transmitter of claim 17 , wherein the crest factor reduction device is an application-specific integrated circuit (ASIC).