JPH0783500B2 - Analog-to-digital converter for composite video signals - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] The present invention apparently converts a digital signal into 1
Regarding an analog / digital converter for a composite video signal with a resolution improved by only one bit, an analog / digital converter for a composite video signal that can be simply configured without providing a circuit necessary for improving the resolution by 1 bit. For the purpose of providing the composite video signal, the amplitude comparator that compares the input composite video signal amplitude value with the reference amplitude value to determine the magnitude is operated in parallel by the number corresponding to the converted digital signal bit number. In the analog / digital converter, a luminance / color signal separation circuit and a color subcarrier reproduction circuit are connected in parallel after the analog / digital converter. A voltage generation circuit having a corresponding cycle and generating a voltage varying with an amplitude corresponding to 1/2 LSB of the converted digital signal is provided. Constitute by feeding the output of the generator to the input side of the analog-digital converter.

[Industrial application field]

The present invention apparently converts the converted digital signal to 1
An analog-to-digital converter for a composite video signal whose resolution is improved by only one bit (hereinafter referred to as analog
Digital converter is abbreviated as A / D converter).

Conventionally, this kind of A / D converter has been apparently improved in resolution by causing an illusion about the eyes of the viewer, probably due to its rather complicated structure. Therefore, even with a simple configuration,
It was desired to develop an A / D converter that can obtain good resolution.

[Conventional technology]

A wideband A / D converter and a D / A converter are used in the video signal processing part of a digital television receiver, which is called a video codec. The sampling frequency of this A / D converter is 10MHz or higher. When the digital signal has, for example, a 7-bit structure, it is necessary to connect 2 ⁷ = 128 comparators used in the A / D converter in parallel to the analog signal. That is, when a predetermined reference voltage is given to all the comparators, it is checked where the output of the comparator is "0" and where it is "1", and a digital signal is obtained from the result. At this time, when the number of bits is increased by 1 bit in order to improve image quality, it is necessary to double the circuit scale of the A / D converter. Therefore, on the display, an A / D converter has been proposed which operates as if it were apparently increased by 1 bit due to the averaging effect of the eyes. It is described in Nikkei McGraw-Hill's magazine, "Nikkei Electronics", November 23, 1981, page 233. That is, every other horizontal scanning line, A / D
The reference voltage used for the converter is 1/2 LSB of the output digital value
It is a technology that biases only the voltage corresponding to. Sixth
In the figure, the vertical axis shows the reference voltage and the analog signal value (horizontal thick line), and the horizontal axis shows the number of bits n and n + after digital value conversion.
1 and 1. The solid line shows the signal conversion situation when there is no bias voltage, and the dotted line shows the conversion situation when a bias voltage is applied. Therefore, 1,0 changes as a digital signal value of the same brightness at a certain time.
Therefore, when the obtained digital value is further converted into an analog value and given to the display, when the entire screen is viewed on the screen, it seems that a converter having one bit more is used due to the averaging effect of the eyes. . At this time, in order to perform a more strict operation, the configuration is as shown in FIG. In FIG. 7, 1 is an input terminal for a television composite video signal, 2 is an A / D converter, 3 is a memory, and 4 is an averaging circuit. The memory 3 stores the signal one line before the current scanning line, and the output of the memory 3 and the signal value at the current scanning line are averaged by the averaging circuit 4 to obtain an output signal.

[Problems to be Solved by the Invention]

When the configuration of FIG. 6 is used, the viewer's vision is used to perform an operation equivalent to increasing the number of bits, so if you look closely at the gray screen, you can see that for each horizontal scanning line. The brightness looks different. As shown in FIG. 7, in order to perform a strict operation, an extra memory / averaging circuit was required, and it was necessary to prepare a memory having a capacity of about 1 Kbyte for a television signal. .

SUMMARY OF THE INVENTION It is an object of the present invention to provide an A / D converter for a composite video signal, which can improve the above-mentioned drawbacks and can be simply configured without providing a circuit necessary for improving the resolution by 1 bit.

[Means for Solving the Problems]

FIG. 1 is a diagram showing the principle configuration of the present invention. In FIG. 1, 5 is an input analog signal terminal, 6 is a reference reference amplitude value generation circuit, 7 is an amplitude comparator group, 8 is a 1/2 LSB voltage generation circuit, 9 is a feedback circuit, and 11 is a luminance / color signal separation. Reference numeral 12 denotes a color subcarrier reproduction circuit.

Analog / digital of the composite video signal in which the amplitude comparator 7 for comparing the amplitude value of the input composite video signal 5 with the reference amplitude value 6 to determine the magnitude is operated in parallel by the number corresponding to the converted digital signal bit number. In the converter, the present invention has the following configuration. That is, a luminance / color signal separation circuit and a color subcarrier reproduction circuit are connected in parallel after the analog / digital converter, and the color subcarrier reproduction circuit has a cycle corresponding to the cycle of the color subcarrier. By including a voltage generating circuit that generates a voltage that fluctuates with an amplitude corresponding to 1/2 LSB of the converted digital signal, the output of the voltage generating circuit is fed back to the input side of the analog-digital converter. is there.

However, FIG. 1 shows the case where the output of the 1/2 LSB voltage generating circuit 8 is fed back to the reference voltage value.

[Action]

Amplitude values that differ from each other by a 1-bit voltage from the comparison reference amplitude generation circuit 6 are input to one terminal of each comparator of the amplitude comparator group 7, and the other terminals of the comparators commonly have a certain time. Input an analog signal. Since a change point of "1" and "0" occurs as an output of the amplitude comparator group 7, the position is detected in a state in which the position is grouped so as to correspond to a binary number from the lower comparison reference amplitude value. . Then, a bit string of "1" and "0" is obtained at each output terminal of the comparator.

At the time of the next signal conversion, the output from the circuit 8 that generates an amplitude voltage value corresponding to 1/2 LSB is superimposed on the output of the circuit 6 and applied to one terminal of the amplitude comparator group 7 to output the output digital value. obtain. Since the voltage value to be superimposed fluctuates according to the cycle of the color subcarrier, even if the analog values are the same, the change point positions of "1" and "0" may differ, and the converted 2 Different radix representations (digital values) occur.

〔Example〕

FIG. 2 shows, as an embodiment of the present invention, a configuration in the case where the input signal is a television composite video signal. In FIG. 2, 2 is an overall A / D converter, 6 is a reference amplitude value generation circuit, 7 is an amplitude comparator group, and 8 is a voltage generation that generates an amplitude voltage value corresponding to 1/2 LSB. Circuit, 10 is a composite video signal extracted from the received television signal, 11 is brightness
A color signal separation circuit, 12 is a color subcarrier reproduction circuit. Third
The figure shows a composite video signal in the case of an NTSC type signal as a television signal. Y is the brightness (luminance) signal and R is the color signal
When (red) and B (blue) are used, the composite video signal is superimposed on the Y signal with the RY and BY signals and changed in four cycles. In the voltage generation circuit 8, the voltage as shown in FIG. 4 is generated corresponding to the cycle of FIG. That is, in the cycle, the + value is set so that the amplitude value becomes large, and in the cycle, the + value is not changed, and in the cycle, the negative value is set. When the color signal is separated and extracted from the composite video signal, the calculation of RY = (−) / 2 BY − (−) / 2 is performed.

Similarly for the luminance signal, Y1 = (+) / 2 Y2 = (+) / 2 is calculated.

With the configuration shown in FIG. 3, since a voltage having an amplitude equivalent to 1/2 LSB is applied to the amplitude value generation circuit 6, 1 / 2L of the input signal is input.
The converted digital value is distributed according to the level corresponding to SB. That is, it operates so that the changed digital value in the comparator group output is increased by 1 bit.

Since the above-described operation is performed for each cycle of the color subcarrier, the level of the luminance signal and the color signal does not change for each scanning line, and the same effect as that of the configuration including the line memory and the averaging circuit is provided. Obtainable.

FIG. 5 shows a modified block diagram of FIG. 2, 13 is a signal adder, and the same reference numerals as those in FIG. In this case, since the voltage corresponding to 1/2 LSB is superimposed as the analog value before A / D conversion, the operation in the comparison circuit is different before and after the superimposition.

〔The invention's effect〕

As described above, according to the present invention, by using the amplitude value corresponding to 1/2 LSB after conversion into the digital signal, it is possible to operate as if the digital value conversion is apparently performed by one bit extra. . In the case of a composite video signal such as a television signal, it is possible to obtain a display without a signal change for each scanning line regardless of a complicated structure using a large capacity memory.

[Brief description of drawings]

FIG. 1 is a diagram showing a principle configuration of the present invention, FIG. 2 is a diagram showing an example for a television signal as an embodiment of the present invention, and FIGS. 3 and 4 are diagrams for explaining the operation of FIG. FIG. 5 is a diagram showing the configuration of another embodiment of the present invention, and FIGS. 6 and 7 are diagrams for explaining the operation of the conventional A / D converter. 1 ... Television composite video signal input terminal 2 ... A / D converter 3 ... Memory, 4 ... Averaging circuit 5 ... Input composite video signal terminal 6 ... Comparison reference amplitude value generation circuit 7 ... … Amplitude comparator group 8 …… 1 / 2LSB voltage generation circuit 9 …… Feedback circuit 11 …… Luminance / color signal separation circuit 12 …… Color subcarrier recovery circuit

Claims (1)

[Claims] Claim: What is claimed is: 1. An analog / composite video signal analog circuit in which a plurality of amplitude comparators for comparing the input composite video signal amplitude value with a reference amplitude value to determine the magnitude are operated in parallel. In the digital converter, a luminance / color signal separation circuit and a color subcarrier reproduction circuit are connected in parallel after the analog / digital converter, and the color subcarrier reproduction circuit corresponds to the cycle of the color subcarrier. A voltage generator circuit having a cycle and generating a voltage varying with an amplitude corresponding to 1/2 LSB of the converted digital signal is provided, and the output of the voltage generator circuit is fed back to the input side of the analog-digital converter. An analog-to-digital converter for composite video signals.