System for and method of reducing transmit signal distortion
Systems and methods relate to providing a transmit signal. The transmit signal can be provided in a transmitter circuit including a main pre-equalizer, a main power amplifier in communication with the main pre-equalizer, a replica pre-equalizer, and a replica power amplifier in communication with the replica pre-equalizer. The replica preamplifier is in communication with the main pre-equalizer, and control signals are provided to the main pre-equalizer to reduce distortion. The control signals are provided in response to an output signal of the replica power amplifier.
1. A transmitter circuit, comprising:
a main pre-equalizer configured to pre-distort a burst signal;
a main power amplifier configured to receive the pre-distorted burst signal and generate an amplified burst signal using the pre-distorted burst signal;
a replica pre-equalizer configured to pre-distort a non-burst signal; and
a replica power amplifier, the replica power amplifier configured to receive the pre-distorted non-burst signal from the replica pre-equalizer and generate an amplified non-burst signal using the pre-distorted non-burst signal, wherein control signals are provided to the main pre-equalizer to pre-distort the burst signal, the control signals being provided using the amplified non-burst signal of the replica power amplifier.
2. The transmitter circuit of claim 1 , further comprising:
a control circuit in communication with the replica preamplifier and configured to provide the control signals.
3. The transmitter circuit of claim 2 , wherein the control circuit comprises a coefficient computing circuit and the control signals are transfer coefficients provided to the main pre-equalizer and are provided by the replica pre-equalizer.
4. The transmitter circuit of claim 3 , further comprising a digital to analog converter disposed between the main pre-equalizer and the main power amplifier.
5. The transmitter circuit of claim 4 , further comprising:
an analog to digital converter disposed between the control circuit and the replica power amplifier; and
a digital to analog converter disposed between the replica pre-equalizer and the replica power amplifier.
6. The transmitter circuit of claim 1 , wherein the main power amplifier provides a burst signal.
7. The transmitter circuit of claim 1 , wherein the main power amplifier provides a transmit signal for a cable modem.
8. A method of amplifying a transmit signal, the method comprising:
pre-distorting a training signal, wherein the training signal is a non-burst signal;
amplifying the training signal in a first amplifier;
using an amplified training signal from the first amplifier to provide a control signal;
pre-distorting the transmit signal using the control signal, wherein the transmit signal is a burst signal; and
amplifying the transmit signal in a second amplifier, the first amplifier having the same or similar configuration to the second amplifier.
9. The method of claim 8 , wherein the control signal is used for pre-distorting the training signal.
10. The method of claim 8 , wherein the training signal is a user defined signal.
11. The method of claim 8 , wherein the second amplifier is operated in a low power mode and has higher distortion when operated in the low power mode without pre-distorting the transmission signal as compared to operation a higher power mode.
12. The method of claim 8 , wherein the second amplifier is a main power amplifier for the transmitter and has substantially the same distortion when operated in the low power mode with pre-distorting the transmission signal as the main amplifier has in a higher power mode.
13. The method of claim 8 , wherein the first amplifier is a scaled-down version of the second amplifier.
14. The method of claim 8 , wherein pre-distorting the training signal, amplifying the training signal in first amplifier, and using an amplified training signal from the first amplifier to provide the control signal is performed in a duty cycle of less than 1 percent.
15. The method of claim 8 , wherein pre-distorting the training signal, amplifying the training signal in first amplifier, and using an amplified training signal from the first amplifier to provide the control signal is performed less often than once per minute.
16. A modem, comprising:
a main pre-distortion circuit configured to pre-distort a transmit signal according to a set of coefficients or a version of the set of the coefficients and provide a first pre-distorted signal;
a main power amplifier configured to amplify the first pre-distorted signal;
a replica pre-distortion circuit configured to pre-distort a training signal according the set of coefficients and provide a second pre-distorted signal, wherein the transmit signal is a burst signal and the training signal is a non-burst signal;
a replica power amplifier configured to amplify the second pre-distorted signal and provide an amplified signal; and
a coefficient computing circuit configured to receive the amplified signal or a version of the amplified signal and provide adjustments to the set of coefficients.
17. The modem of claim 16 , wherein the amplified first pre-distorted signal is provided to a cable modem up link transmit path.
18. The modem of claim 16 , further comprising:
a first digital to analog converter disposed between the main pre-distortion circuit and the main power amplifier;
a second digital to analog converter disposed between the replica pre-distortion circuit and the replica power amplifier; and
an analog to digital converter disposed between the coefficient computing circuit and the replica power amplifier.
19. The modem of claim 16 , wherein the coefficient computing circuit uses a least squares fit or sign matrix inversion technique to provide the set of coefficients and wherein the training signal is provided once every 15 minutes or less for a period of 100 milliseconds or less.