Automatic level control circuit for an ad convertor
AssigneeNEC Corporation
InventorYasuharu Yoshida
Life of this patent
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Abstract
An automatic level control circuit for a multi-level quadrature amplitude-modulated (QAM) demodulator having a QAM detector, which produces baseband in-phase (P) and quadrature (Q) signals in response to an input QAM camer wave, and two analog-digital (A/D) convertors which convert the Q and P signals into two parallel digital signals. Automatic level control of the input level of the baseband signal to the A/D convertor is maintained constant by the combination of a reference signal generator in a feed back loop with each A/D convertor. The A/D convertor produces a decoded digital signal and the reference voltage generator, in response to those signals, provides reference voltage to the A/D convertor that are optimized in response to variations in input signal level.
Claims12
An automatic level control circuit for use in a multi-level signal transmission system comprising an analog-to-digital (A/D) converter for discriminating a demodulated multi-level baseband signal with respect to a plurality of reference levels to produce a plurality of decoded digital signals and an error digital signal, and a reference voltage generator, including logic circuit means, responsive to for providing a reference voltage to said A/D converter to uniformly shift said plurality of reference levels, said reference levels being controlled to optimum ones responsive to a variation in the level of said input signal.
A multi-level QAM demodulator for converting multi-level QAM signal into a plurality of digital data signals including a QAM detector means responsive to an input QAM signal for producing quadrature phase (Q) and in-phase (P) demodulated multi-level baseband signals, a first multi-level discriminator means for discriminating said in-phase demodulated multi-level baseband signal and a second multi-level discriminator means for discriminating said quadrature phase demodulated multi-level baseband signals, each discriminator means operating in response to multiple level reference signals and generating digital output signals and a carrier sync circuit connected to synchronize said output signals and said detector means, the improvement wherein:
- each said first and second multi-level discriminator means is adapted to discriminate a demodulated multi-level baseband signal with respect to a plurality of reference levels and to produce a plurality of decoded digital signals and an error digital signal, and said multi-level reference signals are provided and uniformly changed by at least one reference voltage generator, including logic circuit means, responsive to one of the decoded digital signals and said error digital signal.
Dependencies are inferred from the claim text.