Digital Transmitter With Sample Rate Digital Predistortion
A digital transmitter with sample rate digital predistortion is disclosed. The transmitter includes a digital radio frequency (RF) signal generator configured to receive a baseband digital signal and transform the baseband digital signal to a digital RF signal. The digital transmitter further includes a sample rate predistorter configured to predistort the digital RF signal so as to compensate for distortion associated with the transmitter that is generated subsequent to an output of the sample rate predistorter, and resulting in a digital predistorted RF signal. The digital transmitter further includes a digital to analog converter configured to convert the digital predistorted RF signal to analog, resulting in an analog predistorted RF signal.
1 . A transmitter, comprising:
a digital radio frequency (RF) signal generator configured to receive a baseband digital signal and transform the baseband digital signal to a digital RE signal;
a sample rate predistorter configured to predistort the digital RF signal so as to compensate for distortion associated with the transmitter that is generated subsequent to an output of the sample rate predistorter, and resulting in a digital predistorted RE signal; and
a digital to analog converter (DAC) configured to convert the digital predistorted RE signal to analog, resulting in an analog predistorted RF signal.
2 . The transmitter of claim 1 , wherein:
the digital RE signal includes a plurality of samples that define a modulated carrier having frequency that exceeds a bandwidth of the baseband digital signal, and
the sample rate predistorter is configured to perform the predistortion on at least a subset of the plurality of samples of the digital RF signal.
3 . The transmitter of claim 1 , wherein the transformation of the baseband digital signal includes upsampling and digital frequency translation of the baseband digital signal to generate the digital RF signal.
4 . The transmitter of claim 1 , wherein the transformation of the baseband digital signal includes upsampling and digital modulation of the baseband digital signal to generate the digital RF signal.
5 . The transmitter of claim 1 , further comprising:
an amplifier configured to amplify the analog predistorted RE signal, the amplifier introducing at least some of the distortion.
6 . The transmitter of claim 1 , wherein the distortion is non-linear.
7 . The transmitter of claim 1 , wherein the predistortion of the digital RF signal includes applying a digital delay to the digital RF signal.
8 . The transmitter of claim 1 , wherein the sample rate predistorter is configured to perform the predistortion on the digital RF signal at a sample rate associated with that of the DAC.
9 . The transmitter of claim 1 , wherein the sample rate predistorter is configured to perform the predistortion at a sample rate that is different than that of the DAC.
10 . The transmitter of claim 1 , wherein the sample rate predistorter includes a lookup table to determine, based on most significant bits of the digital RF signal, a base value and a slope value for generating the digital predistorted RF signal.
11 . The transmitter of claim 10 , wherein the sample rate predistorter is configured to multiply the slope value by the least significant bits of the digital RF signal and add the result of the multiplication to the base value to generate a magnitude of the digital predistorted RF signal.
12 . A method, comprising:
receiving a baseband digital signal and transforming the baseband digital signal to a digital radio frequency (RF) signal;
predistorting the digital RF signal so as to compensate for distortion that is generated subsequent to the predistorting, and producing a digital predistorted RF signal; and
converting the digital predistorted RF signal to an analog predistorted RF signal.
13 . The method of claim 12 , wherein:
the digital RF signal includes a plurality of samples that define a modulated carrier having a frequency that exceeds a bandwidth of the baseband digital signal, and
the predistorting includes performing the predistortion on at least a subset of the plurality of samples of the digital RF signal.
14 . The method of claim 12 , wherein the transforming the baseband digital signal includes upsampling and digital frequency translation of the baseband digital signal to generate the digital RF signal.
15 . The method of claim 12 , wherein the transforming the baseband digital signal includes upsampling and digital modulation of the baseband digital signal to generate the digital RF signal.
16 . The method of claim 12 , further comprising:
amplifying the analog predistorted RF signal, wherein the amplifying introduces the distortion.
17 . The method of claim 12 , wherein the distortion is non-linear.
18 . The method of claim 12 , wherein the predistorting includes predistorting the digital RF signal at a sample rate associated with that of the DAC.
19 . The method of claim 12 , the predistorting includes predistorting the digital RF signal at a sample rate that is different than that of the DAC.
20 . The method of claim 12 , wherein the predistorting includes:
using a lookup table to determine, based on most significant bits of the digital RF signal, a base value and a slope value;
multiplying the slope value with the least significant bits of the digital RF signal and adding the result of the multiplication to the base value, to generate a magnitude of the digital predistorted RF signal; and
using the magnitude of the digital predistorted RF signal and a sign of the digital RF signal to generate the digital predistorted RF signal.