Television – Image signal processing circuitry specific to television – Noise or undesired signal reduction
Reexamination Certificate
1998-06-26
2001-09-04
Kostak, Victor R. (Department: 2611)
Television
Image signal processing circuitry specific to television
Noise or undesired signal reduction
C348S723000, C348S470000, C375S297000, C333S149000
Reexamination Certificate
active
06285412
ABSTRACT:
TECHNICAL FIELD
The present invention relates to communication systems and is particularly directed to a system for compensating linear distortion caused by any high speed linear data system, and specifically a digital TV (“DTV”) transmission system.
BACKGROUND OF THE INVENTION
A high-speed data communication system such as a DTV broadcast communication system requires linear equalization for optimum performance and signal coverage. Because of the high data rates required in a DTV system, an adaptive equalization system becomes very difficult to implement using known equalization techniques.
Traditional linear equalization (compensation) for television systems has been accomplished by analog, pre-distortion equalizers which are static (non-adaptive). These equalizers are filters/correctors that require factory adjustments to provide a desired amount of pre-distortion (pre-equalization). Aging of the filters/correctors and temperature change cause drift in the amount of pre-distortion. Occasional field adjustments are required.
Digital signal processing techniques provide improved performance of the pre-equalization of the information signal. Specifically, digital signal processing can be used in an adaptive correction and equalization approach. Such an adaptive approach can eliminate the factory and field adjustments.
It is known to perform adaptive correction of a signal within a signal stream proceeding toward a transmitter. However, in a relatively fast data rate system, the correction requires a relatively large amount of processing in a short period of time. For example, assuming a 64 tap Finite Impulse Response (“FIR”) filter, processing a DTV signal at a 25 Mhz sample rate, the update of the filter requires 64 times 25 million updates per second. This translates to 1.6 billion updates per second. Such an update rate requires that the adaptation process be done offline.
SUMMARY OF THE INVENTION
In accordance with one aspect, the present invention provides an adaptive apparatus for compensating a linear distorting action to an information signal within a non-ideal transmission system. The system includes signal provision means for providing an information signal, and also includes output means. The linear distorting action of the system includes shifting of at least one signal aspect of the signal away from its intended value. In one example, the transmission system is a high-speed data system, and is particularly a DTV broadcast transmission system. In the DTV transmission system, band limiting filters and other system impairments distort signal aspects away from their intended values. The apparatus includes compensator means, located along a signal stream from the signal provision means to the output means, for pre-equalizing the information signal. Sampler means couples off a sample signal from the output means. Determination means, connected to receive the sample signal and the information signal outside of the signal stream from the signal provision means to the output means, determines an amount of pre-equalization by the compensator means to compensate the linear distorting action of the system. Means modifies the pre-equalization caused by the compensator means in response to the determination by the determination means.
In accordance with another aspect, the present invention provides a digital adaptive equalizer circuit for correcting the frequency response of a transmission system. The system includes an output stage with an input digital-to-analog converter circuit for converting digital signals into analog form for transmission as analog signals, and includes a feedback circuit with an analog-to-digital converter for receiving and converting the transmitted output analog signals to digital form. The digital adaptive equalizer circuit includes a first input circuit, with an input memory circuit, for receiving the input digital signals to be transmitted by the transmission system. The digital adaptive equalizer circuit includes a second input circuit, with a feedback memory circuit, for receiving the output signals in digital form from the feedback circuit. A first adaptive digital corrector circuit, having a variable frequency response that is varied by digital signals applied thereto, receives the input digital signals from the first input circuit, modifies the frequency response of the input digital signals, and applies the modified input digital signals to the output stage for transmission. A second adaptive digital corrector circuit, having a variable frequency response that is varied by digital signals applied thereto, receives output digital signals from the feedback memory circuit and modifies the frequency response of the received output digital signals. A comparison circuit compares the input digital signals from the input memory circuit to the output digital signals from the second adaptive corrector filter and applies digital difference signals to the second adaptive digital corrector circuit for controlling the degree of modification applied by the second adaptive digital corrector circuit to the received output digital signals in a direction so as to reduce the difference between the digital input signals and the digital output signals. A control circuit applies digital signals to the first adaptive digital corrector for correcting the first adaptive corrector circuit to the second corrector circuit.
In accordance with another aspect, the present invention provides a digital television broadcast transmitter. The transmitter includes an analog power amplifier circuit. An exciter circuit receives digital television signals and formats the digital television signals in form to be broadcasted by the transmitter. A digital-to-analog converter circuit converts the formatted digital televisions into analog form for application to the power amplifier circuit. A feedback circuit receives output analog television signals from the power amplifier circuit and includes a digital-to-analog converter circuit for converting the output analog television signals into digital form. A first adaptive digital corrector circuit receives the formatted input digital television signals, modifies the formatted input digital television signals, and applies the modified formatted input digital television signals to the digital-to-analog converter circuit. A control circuit includes a second adaptive digital corrector circuit receiving digital output signals from the feedback circuit. The control circuit includes a comparison circuit for comparing the formatted input digital television signals to corresponding modified output digital television signals from the second adaptive digital corrector circuit and applying digital control signals to the second adaptive digital corrector circuit for controlling the degree of modification applied to the received output digital television signals in a direction so as to reduce the difference between the formatted input digital television signals and the digital output television signals. The control circuit also includes a circuit for correlating the modification applied by the first adaptive corrector circuit as a function of the modification applied by the second adaptive corrector circuit.
In accordance with another aspect, the present invention provides a digital adaptive equalizer circuit for modifying input digital signals to be applied to a transmission system that includes an output stage and a feedback circuit for providing output signals from the output stage in digital form. The digital adaptive equalizer circuit includes a first adaptive digital equalizer for receiving the input digital signals and modifying the input digital signals and applying the modified input digital signals to the output stage for transmission. The digital adaptive equalizer circuit includes a control circuit. The control circuit includes a second adaptive digital equalizer receiving digital output signals from the feedback circuit. The control circuit includes a comparison circuit for comparing the input digital signals to corresponding modified outp
Harris Corporation
Kostak Victor R.
Tarolli, Sundheim, Covell Tummino & Szabo L.L.P.
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