Pulse or digital communications – Transmitters
Reexamination Certificate
1998-12-09
2002-06-04
Ghayour, Mohammad H. (Department: 2734)
Pulse or digital communications
Transmitters
C329S354000, C329S349000, C329S351000, C329S320000, C375S296000, C375S285000, C375S254000
Reexamination Certificate
active
06400774
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a nonlinearity-caused distortion compensating system which can be used in, for example, a radio transmitter having a modulator and an RF amplifier. In general, “nonlinearity-caused distortion” is shortened to “nonlinear distortion”.
2. Description of the Related Art
Japanese published unexamined patent application 4-290321 discloses a nonlinearity-caused distortion compensating system (a nonlinear distortion compensating system) used in a radio transmitter having a modulator and an RF amplifier. In Japanese application 4-290321, a digital filter processes a digital baseband signal into a processing-resultant digital signal, and a digital-to-analog converter following the digital filter changes the processing-resultant digital signal into a corresponding analog baseband signal.
In addition, a modulator following the digital-to-analog converter subjects the analog baseband signal to a modulation process, thereby converting the analog baseband signal into a modulation-resultant signal. Furthermore, a first frequency converter following the modulator changes the modulation-resultant signal into a corresponding RF signal. Then, an RF power amplifier following the first frequency converter amplifies the RF signal.
Generally, the input-output characteristic of an RF power amplifier has a nonlinearity which distorts the output signal of the RF power amplifier.
In Japanese application 4-290321, a nonlinearity-caused distortion in the output signal of the RF power amplifier is previously determined. The digital filter includes a ROM storing signals which represent corrective coefficients predetermined to compensate for a nonlinearity-caused distortion in the output signal of the RF power amplifier.
In Japanese application 4-290321, the RF power amplifier is followed by a second frequency converter which changes the output signal of the RF power amplifier into a corresponding IF signal. A demodulator following the second frequency converter subjects the IF signal to a demodulation process, thereby converting the IF signal into a corresponding demodulation-resultant signal. The demodulator extracts a polarity signal and an error signal from the demodulation-resultant signal. A correlator following the demodulator detects a correlation between the polarity signal and the error signal, and outputs a signal representing the detected correlation. An integrator following the correlator integrates the output signal of the correlator into a control signal. The integrator outputs the control signal to the digital filter.
In Japanese application 4-290321, at an initial stage of operation of the transmitter, the digital filter processes the digital baseband signal in response to the corrective coefficients and the control signal so that a nonlinearity-caused distortion in the output signal of the RF power amplifier can be compensated for. During a normal stage of operation of the transmitter which succeeds the initial stage thereof, the digital filter processes the digital baseband signal in response to the control signal only.
Japanese application 4-290321 considers a nonlinearity-caused distortion in the output signal of the RF power amplifier. Generally, the input-output characteristic of a modulator also has a nonlinearity which distorts the output signal of the modulator.
Japanese application 4-290321 fails to consider a nonlinearity-caused distortion in the output signal of the modulator.
SUMMARY OF THE INVENTION
It is an object of this invention to provide a system which can compensate for a signal distortion caused by a nonlinearity of a modulator.
A first aspect of this invention provides a nonlinearity-caused distortion compensating system (a nonlinear distortion compensating system) in a radio transmitter having a quadrature modulating portion and an RF power amplifier. The RF power amplifier follows the quadrature modulating portion. The system comprises a power calculating portion for calculating a value related to a power of a transmission signal from first baseband signals quadrature with respect to each other; first means for determining first distortion compensating coefficients in response to the value calculated by the power calculating portion, the first distortion compensating coefficients being designed to compensate for a signal distortion caused by a nonlinearity of the quadrature modulating portion; second means for determining second distortion compensating coefficients in response to the value calculated by the power calculating portion, the second distortion compensating coefficients being designed to compensate for a signal distortion caused by a nonlinearity of the RF power amplifier; a compensation-coefficient calculating portion for calculating final distortion compensating coefficients from the first distortion compensating coefficients determined by the first means and the second distortion compensating coefficients determined by the second means; a distortion compensating portion for converting the first baseband signals into second baseband signals quadrature with respect to each other in response to the final distortion compensating coefficients calculated by the compensation-coefficient calculating portion to compensate for signal distortions caused by the nonlinearity of the quadrature modulating portion and the nonlinearity of the RF power amplifier; and third means for feeding the second baseband signals generated by the distortion compensating portion to the quadrature modulating portion.
A second aspect of this invention is based on the first aspect thereof, and provides a nonlinearity-caused distortion compensating system wherein the first means includes a first memory for storing signals representing a first reference table providing a relation between the first distortion compensating coefficients and the value calculated by the power calculating portion, and the second means includes a second memory for storing signals representing a second reference table providing a relation between the second distortion compensating coefficients and the value calculated by the power calculating portion.
A third aspect of this invention is based on the first aspect thereof, and provides a nonlinearity-caused distortion compensating system wherein the first means includes a first calculator for calculating the first distortion compensating coefficients from the value calculated by the power calculating portion according to first equations, and the second means includes a second calculator for calculating the second distortion compensating coefficients from the value calculated by the power calculating portion according to second equations.
A fourth aspect of this invention provides a nonlinearity-caused distortion compensating system in a radio transmitter having a quadrature modulating portion and an RF power amplifier. The RF power amplifier follows the quadrature modulating portion. The system comprises a power calculating portion for calculating a value related to a power of a transmission signal from first baseband signals quadrature with respect to each other; first means for determining first distortion compensating coefficients in response to the value calculated by the power calculating portion, the first distortion compensating coefficients being designed to compensate for a signal distortion caused by a nonlinearity of the quadrature modulating portion; second means for determining second distortion compensating coefficients in response to the value calculated by the power calculating portion according to a relation therebetween, the second distortion compensating coefficients being designed to compensate for a signal distortion caused by a nonlinearity of the RF power amplifier; a compensation-coefficient calculating portion for calculating final distortion compensating coefficients from the first distortion compensating coefficients determined by the first means and the second distortion compensating coefficients determined by the second means; a distortion compensating porti
Matsuoka Akihiko
Orihashi Masayuki
Connolly Bove & Lodge & Hutz LLP
Ghayour Mohammad H.
LandOfFree
Nonlinearity-caused distortion compensating system does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Nonlinearity-caused distortion compensating system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Nonlinearity-caused distortion compensating system will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2918422