Linearization of amplifiers using baseband detection and non-baseband pre-distortion
In an amplifier system that linearizes an amplifier by pre-distorting the input signal prior to amplification, a baseband pre-distortion processor processes the input signal in a digital baseband domain to generate one or more pre-distortion parameters based on the power of the digital baseband input signal. The digital baseband signal is up-converted and D/A-converted into a non-baseband (e.g., IF or RF) signal which is then pre-distorted, e.g., using a phase/gain adjuster or a vector modulator. By generating the pre-distortion parameters at baseband, while pre-distorting the input signal at non-baseband, the amplifier system avoids the cost and inaccuracies associated with analog signal delay and RF power detection of prior-art “all-RF” pre-distortion implementations, while avoiding the wider-bandwidth filtering of prior-art “all-baseband” pre-distortion implementations.
1. An apparatus adapted to pre-distort an input signal prior to application to an amplifier such that the amplifier will generate a linearized amplified output signal, the apparatus comprising:
a processor adapted to operate in a digital baseband domain to generate one or more pre-distortion parameters for the input signal, wherein the processor is adapted to detect power in a digital baseband signal corresponding to the input signal and generate the one or more pre-distortion parameters based on the detected power; and
a pre-distorter adapted to pre-distort the input signal in a non-baseband domain based on the one or more pre-distortion parameters.
2. The apparatus of claim 1 , wherein the pre-distorter is adapted to pre-distort the input signal in an analog non-baseband domain.
3. The apparatus of claim 2 , wherein the pre-distorter comprises a phase/gain adjuster or a vector modulator.
4. The apparatus of claim 1 , wherein the non-baseband domain is an RF domain.
5. The apparatus of claim 1 , wherein the non-baseband domain is an IF domain.
6. The apparatus of claim 1 , wherein the processor is adapted to retrieve the one or more pre-distortion parameters from a look-up table (LUT) based on the detected power.
7. The apparatus of claim 1 , further comprising a low-pass filter (LPF) located between the processor and the pre-distorter, wherein the bandwidth of the LPF is comparable to the bandwidth of the input signal.
8. The apparatus of claim 7 , further comprising an IF-to-RE up-converter located after the LPF and a band-pass filter (BPF) located after the up-converter and before the pre-distorter, wherein the bandwidth of the BPF is comparable to the bandwidth of the input signal.
9. The apparatus of claim 7 , further comprising an IF-to-RE up-converter located after the pre-distorter and a BPF located after the up-converter.
10. The apparatus of claim 1 , wherein the processor is adapted to digitally delay the input signal.
11. The apparatus of claim 1 , wherein:
the processor is adapted to:
convert a digital baseband input signal into a digital intermediate frequency (IF) signal;
detect power in the digital baseband input signal; and
retrieve one or more digital pre-distortion parameters from a LUT based on the detected power;
apparatus further comprises:
a digital-to-analog converter (DAC), for each digital pre-distortion parameter, adapted to convert the corresponding digital pre-distortion parameter into an analog pre-distortion signal;
another DAC adapted to convert the digital IF signal into an analog IF signal;
an LPF adapted to low-pass filter the analog IF signal;
an up-converter adapted to convert the filtered analog IF signal into an RE signal;
a BPF adapted to band-pass filter the RE signal; and
a low-power amplifier adapted to amplify the filtered RE signal, wherein:
the pre-distorter is adapted to pre-distort the amplified RE signal at RE based on the one or more analog pre-distortion signals to generate the pre-distorted input signal to be applied to the amplifier.
12. The apparatus of claim 11 , wherein:
the processor is adapted to digitally delay the digital baseband input signal;
the bandwidth of the LPF is comparable to the bandwidth of the input signal; and
the bandwidth of the BPF is comparable to the bandwidth of the input signal.
13. The apparatus of claim 1 , wherein:
the processor is adapted to:
convert a digital baseband input signal into a digital IF signal;
detect power in the digital baseband input signal; and
retrieve one or more digital pre-distortion parameters from a LUT based on the detected power;
the apparatus further comprises:
a DAC, for each digital pre-distortion parameter, adapted to convert the corresponding digital pre-distortion parameter into an analog pre-distortion signal;
another DAC adapted to convert the digital IF signal into an analog IF signal; an LPF adapted to low-pass filter the analog IF signal, wherein:
the pre-distorter is adapted to pre-distort the filtered IF signal at IF based on the one or more analog pre-distortion signals to generate a pre-distorted IF signal;
an up-converter adapted to convert the pre-distorted IF signal into a pre-distorted RF signal;
a BPF adapted to band-pass filter the pre-distorted RE signal; and
a low-power amplifier adapted to amplify the filtered pre-distorted RE signal to generate the pre-distorted input signal to be applied to the amplifier.
14. The apparatus of claim 13 , wherein:
the processor is adapted to digitally delay the digital baseband input signal; and
the bandwidth of the LPF is comparable to the bandwidth of the input signal.
15. A method for pre-distorting an input signal for application to an amplifier such that the amplifier will generate a linearized amplified output signal, the method comprising:
operating in a digital baseband domain to generate one or more pre-distortion parameters for the input signal, wherein the operating comprises (i) detecting power in a digital baseband signal corresponding to the input signal and (ii) generating the one or more pre-distortion parameters based on the detected power; and
pre-distorting the input signal in a non-baseband domain based on the one or more pre-distortion parameters.
16. The method of claim 15 , further comprising amplifying the pre-distorted input signal to generate the linearized amplified output signal.
17. The apparatus of claim 1 , further comprising the amplifier.
18. A pre-distortion sub-system adapted to pre-distort an input signal prior to application to an amplifier such that the amplifier will generate a linearized amplified output signal, the pre-distortion sub-system comprising:
a processor adapted to operate in a digital baseband domain to generate one or more pre-distortion parameters for the input signal;
a pre-distorter adapted to pre-distort the input signal in a non-baseband domain based on the one or more pre-distortion parameters; and
a low-pass filter (LPF) located between the processor and the pre-distorter, wherein the bandwidth of the LPF is comparable to the bandwidth of the input signal.
19. The sub system of claim 18 , further comprising an IF-to-RE up-converter located after the LPF and a band-pass filter (BPF) located after the up-converter and before the pre-distorter, wherein the bandwidth of the BPF is comparable to the bandwidth of the input signal.
20. The sub system of claim 18 , further comprising an IF-to-RE up-converter located after the pre-distorter and a BPF located after the up-converter.