Digital pre-distortion systems in transmitters
Various digital pre-distortion systems for use in transmitters are disclosed. The digital pre-distortion system comprises an observing path, which performs either undersampling or radio frequency sampling of the output of a power amplifier. Undersampling may be performed at a rate, which causes aliasing to occur in the undersampled frequency domain. Both undersampling and radio frequency sampling reduces the complexity of the digital pre-distortion system by removing any down mixing modules or anti-aliasing modules, while maintaining reasonable performance of the digital pre-distortion systems.
1. A digital pre-distortion circuitry for observing and correcting non-linearity in a transmitter, the digital pre-distortion circuitry comprising:
an observing path configured to sample a multi-band output signal of a power amplifier, said observing path comprising a radio frequency (RF) analog-to-digital converter (ADC) configured to sample the multi-band output signal of the power amplifier at a first sampling rate that is equal to or more than twice a highest upper cut off frequency of a band centered at a highest frequency of the multi-band output signal to produce a multi-band digital signal without overlapping between bands, wherein the observing path does not convert the multi-band output signal of the power amplifier to an intermediate frequency; and
a digital signal processing circuit for down sampling, in a digital domain, the multi-band digital signal produced by the RF ADC to generate a down sampled multi-band digital signal having a sampling rate that matches the transmitter and is lower than the first sampling rate, and measuring the non-linearity of the power amplifier based on the down sampled multi-band digital signal.
2. The digital pre-distortion circuitry of claim 1 , wherein:
the observing path does not include an anti-aliasing filter.
3. The digital pre-distortion circuitry of claim 1 , wherein:
the digital signal processing circuit is configured to remove artifacts and/or noise caused by the sampling process of the RF ADC through an adaptive algorithms engine configured to compare known multi-band signals being transmitted in a path towards the power amplifier and the multi-band digital signal respectively.
4. The digital pre-distortion circuitry of claim 1 , wherein the digital signal processing circuit comprises:
a multi-band separation engine comprising bandpass filters configured to separate the multi-band digital signal into separated bands.
5. The digital pre-distortion circuitry of claim 4 , wherein the digital signal processing circuit further comprises at least two adaptive algorithms engines configured to process the separated bands in parallel to compare at least one known multi-band signals being transmitted in a path towards the power amplifier and at least one respective separated bands to measure and/or correct the non-linearity of the power amplifier.
6. The digital pre-distortion circuitry of claim 4 , wherein the digital signal processing circuit further comprises one or more adaptive engines configured to process the separated bands one band at a time or a subset of the separated bands at a time to compare at least one known multi-band signals being transmitted in a path towards the power amplifier and at least one respective separated bands to measure and/or correct the non-linearity of the power amplifier.
7. The digital pre-distortion circuitry of claim 1 , wherein:
the digital signal processing module comprises a multi-band separation engine configured to separate the multi-band digital signal into M separated bands using known multi-band signals being transmitted in a path towards the power amplifier respective to the M bands.
8. The digital pre-distortion circuitry of claim 7 , wherein the digital signal processing circuit further comprises at least two adaptive algorithms engines configured to process the separated bands in parallel to compare at least one known multi-band signals being transmitted in a path towards the power amplifier and at least one respective separated bands to measure and/or correct the non-linearity of the power amplifier.
9. The digital pre-distortion circuitry of claim 7 , wherein the digital signal processing circuit further comprises one or more adaptive engines configured to process the separated bands one band at a time or a subset of the separated bands at a time to compare at least one known multi-band signals being transmitted in a path towards the power amplifier and at least one respective separated bands to measure and/or correct the non-linearity of the power amplifier.
10. The digital pre-distortion circuitry of claim 1 , wherein the sampling rate is at least 2 gigahertz.
11. A digital pre-distortion method for observing and correcting non-linearity in a transmitter, the method comprising:
sampling a multi-band output signal of a power amplifier in an observing path by a radio frequency (RF) analog-to-digital converter (ADC) at a first sampling rate that is equal to or more than twice a highest upper cut off frequency of a band centered at a highest frequency of the multi-band output signal to produce a multi-band digital signal wherein sampling in the observing path does not include converting the multi-band the output signal of the power amplifier to an intermediate frequency, wherein sampling in the observing path does not include converting the multi-band the output signal of the power amplifier to an intermediate frequency; and
down sampling, by the digital signal processing circuit in a digital domain, the multi-band digital signal produced by the RF ADC to generate a down sampled multi-band digital signal having a sampling rate that matches the transmitter and is lower than the first sampling rate;
measuring, by the digital signal processing circuit, the non-linearity of the power amplifier using a signal being transmitted in a forward path and the down sampled multi-band digital signal; and
correcting, by the digital signal processing circuit, the non-linearity of the power amplifier.
12. The digital pre-distortion method of claim 11 , wherein sampling in the observing path does not include an anti-aliasing filter.
13. The digital pre-distortion method of claim 11 , further comprising:
removing, by the digital signal processing circuit, artifacts and/or noise caused by the sampling process of the RF ADC through an adaptive algorithms engine configured to compare known multi-band signals being transmitted in a path towards the power amplifier and the multi-band digital signal respectively.
14. The digital pre-distortion method of claim 11 , further comprising:
separating the multi-band digital signal into separated bands by a multi-band separation engine comprising bandpass filters.
15. The digital pre-distortion method of claim 14 , further comprising:
processing, by at least two adaptive algorithms engines of the digital signal processing circuit, the separated bands in parallel to compare at least one known multi-band signals being transmitted in a path towards the power amplifier and at least one respective separated bands to measure and/or correct the non-linearity of the power amplifier.
16. The digital pre-distortion method of claim 15 , further comprising:
processing, by one or more adaptive engines of the digital signal processing circuit, the separated bands one band at a time or a subset of the separated bands at a time to compare at least one known multi-band signals being transmitted in a path towards the power amplifier and at least one respective separated bands to measure and/or correct the non-linearity of the power amplifier.
17. The digital pre-distortion method of claim 11 , further comprising:
separating, by a multi-band separation engine in the digital signal processing module, the multi-band digital signal into M separated bands using known multi-band signals being transmitted in a path towards the power amplifier respective to the M bands.
18. The digital pre-distortion method of claim 17 , further comprising:
processing, by at least two adaptive algorithms engines of the digital signal processing circuit, the separated bands in parallel to compare at least one known multi-band signals being transmitted in a path towards the power amplifier and at least one respective separated bands to measure and/or correct the non-linearity of the power amplifier.
19. The digital pre-distortion method of claim 17 , further comprising:
processing, by one or more adaptive engines of the digital signal processing circuit, the separated bands one band at a time or a subset of the separated bands at a time to compare at least one known multi-band signals being transmitted in a path towards the power amplifier and at least one respective separated bands to measure and/or correct the non-linearity of the power amplifier.
20. A transmitter with digital pre-distortion for observing and correcting non-linearity in the transmitter, the apparatus comprising:
a forward path to transmit a multi-band signal towards a power amplifier, wherein the desired multi-band signal has a first sampling rate;
an observing path to sample a multi-band output signal of the power amplifier, said observing path comprising a radio frequency (RF) analog-to-digital converter (ADC) configured to sample the multi-band output signal of the power amplifier at a second sampling rate that is equal to or more than twice a highest upper cut off frequency of a band centered at a highest frequency of the multi-band output signal, wherein the observing path does not convert the multi-band output signal of the power amplifier to an intermediate frequency; and
a digital signal processing circuit to lower the second sampling rate of the multi-band digital signal from RF ADC in a digital domain to generate a down sampled multi-band digital signal having a lower sampling rate that matches the first sampling rate and measuring the non-linearity of the power amplifier by comparing the multi-band signal in the forward path and the down sampled multi-band digital signal.