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 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 band-pass filter characterized by a third bandwidth coupled to the output of the power amplifier;
a down-converter coupled to the output of the band-pass filter;
an analog-to-digital converter (ADC) coupled to the output of the down-converter, wherein the ADC is characterized by a sampling rate value less than a value of the first bandwidth; and
a digital filter coupled to the polynomial function generators in the indirect learning algorithm.
2. The wideband communications system of claim 1 wherein the ADC is characterized by a sampling rate value less than one-third the value of the first bandwidth.
3. The wideband communications system of claim 1 wherein the third bandwidth is less than the first bandwidth.
4. The wideband communications system of claim 3 wherein the third bandwidth is substantially equal to the second bandwidth.
5. The wideband communications system of claim 1 wherein the band-pass filter comprises a low power narrowband band-pass filter.
6. The wideband communications system of claim 1 wherein the filter comprises a narrowband digital filter.
7. The wideband communications system of claim 1 wherein the band-pass filter comprises a radio frequency (RF) filter.
8. The wideband communications system of claim 1 wherein the band-pass filter comprises an analog lower power narrowband intermediate frequency (IF) filter.
9. 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;
a radio frequency (RF) band-pass filter coupled to the output of the power amplifier and characterized by a bandwidth less than 100 MHz;
an analog-to-digital converter (ADC) coupled to the output of the RF band-pass filter, wherein the ADC is characterized by a sampling rate less than or equal to 100 Msps; and
a digital filter coupled to the polynomial function generator in the indirect learning algorithm.
10. The communications system of claim 9 wherein the bandwidth of the RF band-pass filter is between 30 MHz and 50 MHz.
11. The communications system of claim 9 wherein the sampling rate is between 60 Msps and 100 Msps.
12. A method of operating a communications system, the method comprising:
receiving a signal at a digital predistorter (DPD);
introducing predistortion to the signal using the DPD;
filtering the predistorted signal using a digital filter;
converting the filtered signal to an analog signal;
modulating the analog signal;
amplifying the modulated signal;
coupling a portion of the amplified signal to provide a feedback signal;
filtering the feedback signal using a band-pass filter;
downconverting the filtered feedback signal;
converting the downconverted signal to a digital signal; and
providing the digital signal to the DPD.
13. The method of claim 12 wherein filtering the predistorted signal is performed over a filter bandwidth less than the bandwidth of the DPD.
14. The method of claim 13 wherein the filter bandwidth is between 30 MHz and 50 MHz.
15. The method of claim 14 wherein filtering the feedback signal using a band-pass filter is performed over a band-pass bandwidth less than the bandwidth of the DPD.
16. The method of claim 13 wherein the band-pass bandwidth is between 30 MHz and 50 MHz.
17. The method of claim 12 wherein converting the downconverted signal is performed at a sampling rate less than twice the bandwidth of the DPD.
18. The method of claim 17 wherein the sampling rate is between 60 Msps and 100 Msps.