US 4,543,599 AGranted

Analog-to-digital conversion apparatus including double dither signal sources

AssigneeRCA Corporation

InventorsDonald H. Willis, Russell T. Fling

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Abstract

Digital representations of analog signals are limited in resolution accuracy by the number of bits in the digital output signal of an analog-to-digital converter which limits the number of analog output levels produceable by a digital-to-analog converter. The apparent resolution accuracy can be improved, however, by the addition of two "dithering" signals, one at a lower frequency and one at a higher frequency, to increase the number of transitions of the least significant bit (LSB) of the digital signals. In a television receiver employing digital signal processing apparatus, dither signals having magnitudes equivalent to 1/2 and 1/4 LSB and at frequencies related to the TV line frequency and the color subcarrier frequency are preferred.

Claims6

Dependent claims

In a television receiver, apparatus for producing digital samples representative of the magnitude of analog composite video signals which have a line rate associated therewith and which include a reference frequency signal component, comprising:

a clocking source for providing sampling signals having a frequency related to that of said reference frequency signal component;
a reference source for providing a reference level signal;
converting means, coupled for receiving said composite video signals and coupled to said clocking and reference sources, for developing said digital samples in response to said sampling signals and said reference level signal;
first means, coupled to said converting means, for changing the magnitude of one of said composite video signals and said reference level signal at a first periodic rate substantially equal to one-half of said line rate, which changing the magnitude is by a first amount smaller than that represented by the least significant bit of said digital samples;
and
second means, coupled to said converting means for changing the magnitude of one of said composite video signals and said reference level signal at a second periodic rate substantially equal to one-half of the frequency of said reference frequency signal component, which changing the magnitude is by a second amount smaller than that represented by the least significant bit of said digital samples and different from said first amount.

3 more elements

Dependencies are inferred from the claim text.