Wide bandwidth digital predistortion system with reduced sampling rate
A digital predistortion linearization method is provided for increasing the instantaneous or operational bandwidth for RF power amplifiers employed in wideband communication systems. Embodiments of the present invention provide a method of increasing DPD linearization bandwidth using a feedback filter integrated into existing digital platforms for multi-channel wideband wireless transmitters. An embodiment of the present invention utilizes a DPD feedback signal in conjunction with a low power band-pass filter in the DPD feedback path.
1. A communications system comprising:
a digital predistorter (DPD) operable to receive an input signal, wherein the input signal is characterized by a bandwidth of 20 MHz and the DPD is characterized by a bandwidth of greater than 100 MHz;
a digital filter coupled to the output of the DPD, wherein the digital filter is characterized by a bandwidth between 30 MHz and 50 MHz;
a digital-to-analog converter coupled to the output of the digital filter;
a modulator coupled to the output of the digital-to-analog converter;
a power amplifier coupled to the output of the modulator;
an intermediate frequency (IF) band-pass filter coupled to the output of the power amplifier and the output of a down-converter, wherein the IF band-pass filter is characterized by a bandwidth less than 100 MHz; and
an analog-to-digital converter (ADC) coupled to the output of the IF band-pass filter, wherein the ADC is characterized by a sampling rate less than or equal to 100 Msps,
wherein the DPD comprises a coefficient estimator applying an indirect learning algorithm.
2. The communications system of claim 1 , wherein the bandwidth of the IF band-pass filter is between 30 MHz and 50 MHz.
3. The communications system of claim 1 , wherein the sampling rate is between 60 Msps and 100 Msps.
4. The communications system of claim 1 , wherein the ADC is characterized by a sampling rate value less than one-third the value of the DPD.
5. The communications system of claim 1 , wherein the bandwidth of the ADC is equal to the bandwidth of the digital filter.
6. The communications system of claim 1 , wherein the digital filter comprises a narrowband digital filter.
7. The communications system of claim 1 , further comprising a duplexer coupled to the output of the power amplifier.
8. The communications system of claim 7 , wherein the duplexer is coupled to the IF band-pass filter.
9. A wideband communications system including:
a digital predistorter (DPD) operable to receive an input signal, wherein the DPD is characterized by a first bandwidth;
a filter characterized by a second bandwidth coupled to the output of the DPD;
a digital-to-analog converter coupled to the output of the filter;
a modulator coupled to the output of the digital-to-analog converter;
a power amplifier coupled to the output of the modulator;
a down-converter coupled to the output of the power amplifier;
a band-pass filter characterized by a third bandwidth coupled to the output of the down-converter; and
an analog-to-digital converter (ADC) coupled to the output of the band-pass filter, wherein the ADC is characterized by a sampling rate value less than a value of the first bandwidth,
wherein the DPD comprises a coefficient estimator applying an indirect learning algorithm.
10. The wideband communications system of claim 9 wherein the ADC is characterized by a sampling rate value less than one-third the value of the first bandwidth.
11. The wideband communications system of claim 9 wherein the third bandwidth is less than the first bandwidth.
12. The wideband communications system of claim 11 wherein the third bandwidth is substantially equal to the second bandwidth.
13. The wideband communications system of claim 9 wherein the band-pass filter comprises an intermediate frequency (IF) band-pass filter.
14. The wideband communications system of claim 9 wherein the filter comprises a narrowband digital filter.
15. The wideband communications system of claim 9 , further comprising a duplexer coupled to the output of the power amplifier.