Amplifiers – Hum or noise or distortion bucking introduced into signal...
Reexamination Certificate
2000-04-07
2001-09-04
Pascal, Robert (Department: 2817)
Amplifiers
Hum or noise or distortion bucking introduced into signal...
C330S010000, C332S162000, C375S297000, C455S126000
Reexamination Certificate
active
06285255
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
This invention relates to the art of AM radio broadcasting and, more particularly, to providing adaptive compensation for carrier signal phase distortion caused by amplitude modulation of a RF carrier signal.
2. Description of the Prior Art
The U.S. patents to H. I. Swanson U.S. Pat. Nos. 4,952,890 and 5,132,637 disclose amplitude modulators for use in AM radio broadcasting wherein the modulator serves to generate an amplitude modulated signal by selectively turning on and off a plurality of RF amplifiers to produce amplitude modulation. Each of the RF amplifiers includes a plurality of switching transistors, each of which may take the form of a MOSFET transistor, connected together in a bridge circuit. It is known that amplitude modulating an RF carrier signal with an amplitude varying signal will result in the output carrier signal being shifted in phase from that of the input carrier signal by an amount that varies with the magnitude of the amplitude varying signal. This carrier phase error or distortion in the modulators results in part because the turn on and turn off delays are not constant as the gain of the amplifier is changing. This problem becomes particularly significant where such transmitters are required to pass a phase modulated signal such as stereo CQAM or digital in-band on channel (IBOC) digital radio signals.
In the prior art as illustrated herein in
FIG. 1
, it is known to provide some compensation for such phase distortion by pre-distorting the input. This is not an adaptive system and phase correction using this approach is limited and is load dependent. The aforesaid patent to Swanson U.S. Pat. No. 4,952,890 provides forward phase correction similar to that of
FIG. 1
herein. Also, the aforementioned patent to Swanson U.S. Pat. No. 5,132,637, while employing adaptive feedback circuitry for correcting for distortions due to power supply variations, does not respond to the amplitude of the input audio signal for adaptively correcting for carrier phase distortions due to amplitude modulation of the carrier signal.
The U.S. patent to McGann U.S. Pat. No. 5,121,077 discloses an RF power amplifier wherein a sample of the output is compared with a sample of the RF drive signal with a phase detector which, in turn, drives a phase shifter to shift the phase of the signal applied to the power amplifier. However, there is no teaching of providing a correction signal to the phase shifter based on the magnitude of an amplitude varying input signal.
SUMMARY OF THE INVENTION
In accordance with the present invention, a circuit is provided for adaptively compensating for carrier signal phase distortion caused by amplitude modulating an RF carrier signal. The circuit includes a modulator-amplifier network that receives an RF carrier signal and modulates it by a received amplitude varying signal to obtain therefrom an output modulated RF carrier signal that is phase shifted from the phase of the carrier signal applied to the network and wherein the amount of phase shift is a function of the value of the received amplitude varying signal A phase shifter receives an RF carrier signal and phase shifts it in accordance with the value of a received phase correction signal to provide a pre-phase shifted carrier signal that is applied to the modulator-amplitude network that provides the output modulated RF carrier signal. A phase detector receives and compares the output modulated RF carrier signal and the carrier signal and provides an error signal in accordance with the comparison. An adaptive controller provides the correction signal and it receives the error signal as well as the amplitude varying signal and varies the value of the correction signal in accordance with the values of the error signal and the amplitude varying signal.
REFERENCES:
patent: 4600892 (1986-07-01), Wagner et al.
patent: 4952890 (1990-08-01), Swanson
patent: 5049832 (1991-09-01), Cavers
patent: 5121077 (1992-06-01), McGann
patent: 5132637 (1992-07-01), Swanson
patent: 5247542 (1993-09-01), Onodera et al.
patent: 5798674 (1998-08-01), Fountain
Duello Wayne Douglas
Luu Ky Thoai
Posey Douglas J.
Choe Henry
Harris Corporation
Pascal Robert
Tarolli, Sundheim, Covell Tummino & Szabo L.L.P.
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