JPH0573315B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a digital signal processing circuit for color difference signals of a color television receiver.

BACKGROUND ART In recent years, with the decline in memory prices, digital signal processing circuits that utilize memory have been introduced into television receivers. for example,
It is picture-in-picture. (Television Society Technical Report “Monitor in Television”)
TEBS99−2 S.55.9.20) In such applications,
Generally, luminance signals and color difference signals are handled as analog input/output signals. The reason is that the memory capacity of the band-compressed signal can be reduced, and since it is a component signal, it is easier to compress the time axis.

The following is an example of a digital signal processing circuit for color difference signals of a conventional color television receiver.
This will be explained with reference to the figures.

FIG. 4 shows a digital signal processing circuit for color difference signals of a conventional color television receiver. 1 is an analog color difference signal input terminal, 2 to 4 are transistors, 5 is a voltage source, 6 is a capacitor, 7 is a clamping pulse input terminal, 8 is an A/D converter, 9 is a signal processing circuit section, and 10 is an output A selection switch, 11 is an output selection switch control pulse input terminal, 12 is a D/A converter, and 13 is an analog color difference signal output terminal.

Regarding the digital signal processing circuit for the color difference signals of the conventional color television receiver configured as described above, the following will be described with reference to the waveform diagram in FIG.
Let's explain its operation. Waveform a is an example of the waveform of the analog color difference signal input terminal 1. During the horizontal retrace period, a constant potential is used as a reference, and the video signal is expressed as a potential difference with respect to this potential. Waveform b is the waveform of the clamping pulse input terminal 7, and is a pulse of the horizontal retrace period H of the analog color difference signal of waveform a. When the clamp pulse input terminal 7 is “H”, the transistor 3
conducts, the base of the transistor 4 is fixed at the potential of the voltage source 5, and when it is "L", the alternating current component with respect to that potential is input to the A/D converter 8. In other words, the signal at the analog color difference signal input terminal 1 is translated in direct current to a suitable potential for the A/D converter 8 determined by the voltage source 5 through a clamp circuit composed of transistors 2 to 4. Since the reference potential of the color difference signal is at the center, this convenient potential is the potential at the center of the input range of the A/D converter 8. In this way, the A/D converter 8
The digital signal thus obtained is processed by the signal processing circuit section 9. Since memory is frequently used in the signal processing circuit section 9, it is desirable to reduce the amount of information to reduce the memory capacity. Therefore, it is common to treat only the portion of waveform a excluding the horizontal retrace period. Here, it is assumed that only the signal during the period in which the waveform c of the control pulse input terminal 11 of the output selection switch 10 is "H" is handled. During the period when the signal of waveform c is "H", the output selection switch 10 transmits the data from the signal processing circuit section 9 to the D/A converter 12, and during the "L" period, the output selection switch 10 transmits the data from the signal processing circuit section 9 to the D/A converter 12, and during the period when the signal of waveform c is "L", it transmits the clamp reference data, for example, the data length is 5. In the case of bits, the middle 15 (01111) of 0 to 31 is transmitted to the D/A converter 12. The waveform d is an example of the waveform of the analog color difference signal output terminal 13, and the period when the waveform c is "L" is the clamp reference potential.

Problems to be Solved by the Invention However, in the above configuration, the clamp reference potential in the analog output signal deviates due to quantization error. When the data length is 5 bits, even if the clamp reference data is selected to an optimal value, an error of 1/2 ⁿ or less is unavoidable, considering variations in parts of the clamp circuit. Since the color difference signal of a color television signal uses relative amplitude with respect to a clamp reference potential as information for color reproduction, this error causes a problem in that the hue and the like shift.

SUMMARY OF THE INVENTION In view of the above problems, the present invention provides a digital signal processing circuit that reduces quantization errors in potentials that serve as a reference for analog output signals.

Means for Solving the Problems In order to solve the above problems, the digital signal processing circuit of the present invention includes a circuit that clamps an analog signal and converts it from analog to digital, a voltage source that can vary the clamping potential, and the above-mentioned circuit. A signal processing unit that processes output data of the A/D converter, a data setting switch, an output selection switch that selects the output of the data setting switch or the signal processing unit, and a signal processing unit that is connected to the output terminal of the output selection switch. and a D/A converter.

Effect The present invention has the above-described configuration, and by adjusting the input clamp circuit of the A/D converter and the data setting switch in front of the D/A converter, the reference potential in the analog output signal is quantized. Errors can be reduced.

Embodiment Hereinafter, a digital signal processing circuit according to an embodiment of the present invention will be described with reference to the drawings. 1st
The figure shows a block diagram of an embodiment of the present invention.

In FIG. 1, 1 to 4 and 6 to 13 are the same as in FIG. 4, so their explanation will be omitted. 14 is a variable voltage source for setting a potential for clamping the signal from the analog color difference signal input terminal 1; A data setting switch 15 sets the clamp reference potential of the signal from the analog color difference signal output terminal 13 as digital data.

The digital signal processing circuit configured as above will be explained below with reference to FIGS. 2 and 3. FIG. 3 is a diagram showing the relationship between the clamp reference potential and the input potential of the A/D converter 8 and the D/A converter 1.
The relationship between the output potential of No. 2 and the data of the data setting switch 15 is shown. First, assume that the clamp reference potential at the input of the A/D converter 8 is V2. On the other hand, if the clamp reference data of the data setting switch 15 is set to 0111, then the D/A
The clamp reference potential at the output of converter 12 is
It is VB. Simply setting the data of the data setting switch 15 to 10,000, the output of the D/A converter 12 becomes VA, which is the range of analog input voltage that is determined to be 10,000 considering the input of the A/D converter 8. It corresponds to V0 at the center of V1 to V3, and the difference with V2 remains. Therefore, the clamp reference potential at the input of the A/D converter 8 is adjusted to V0 by the following adjustment procedure. First, for adjustment, the clamping pulse input terminal 7 is constantly set to H.
The A/D converter 8 always has a clamp reference potential.
V2 is supplied.

At this time, if the data setting switch 15 is 01111, the analog color difference signal output terminal 13 will have VB when the output selection switch control pulse input terminal 11 is L, and VA when it is H, as shown in waveform e in FIG. Become. In other words, this indicates that the potential of the variable voltage source 14 is too high. Therefore, the potential of the variable voltage source 14 is lowered. When the voltage is lowered to V3, the analog color difference signal output terminal 13 outputs direct current (VB) as shown in waveform f. The potential of the variable voltage source 14 at that time
By setting the potential V4 to be 1/2LSB lower than V3, the quantization error of the clamp reference potential can be absorbed. By switching the data setting switch 15 at the start of adjustment, it is possible to perform mass production in which the potential of the variable voltage source 14 is always adjusted in the same direction. With the color difference signal of a color TV, there is no problem even if the entire signal is shifted up or down, and the reference potential does not need to be exactly 01111, which further simplifies the adjustment.

Effects of the Invention As described above, according to the present invention, by providing a fine adjustment circuit for the clamp potential at the A/D converter input and a clamp data setting switch, when an A/D converter with a small number of bits is used. However, it is possible to realize a digital signal processing circuit for color difference signals of color television with good color reproduction.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a digital signal processing circuit according to an embodiment of the present invention, FIG. 2 is a waveform diagram of each part in FIG. 1, FIG. 3 is a diagram showing the relationship between the clamp reference potentials in FIG. FIG. 4 is a block diagram of a conventional digital signal processing circuit. DESCRIPTION OF SYMBOLS 1... Analog color difference signal input terminal, 7... Pulse input terminal for clamp, 8... A/D converter, 9... Signal processing circuit section, 10... Output selection switch, 11... Control pulse input terminal, 122... D/A conversion vessel, 13
...Analog color difference signal output terminal, 14...Variable voltage source, 15...Data setting switch.

Claims (1)

[Claims] 1 An A/D converter that clamps an analog signal and converts it to A/D, and a potential to be clamped to the A/D converter.
a voltage source that can be varied continuously in a range that is less than or equal to the resolution of the converter; a signal processing section that processes the output data of the A/D converter; a data setting switch that sets a clamp reference potential; and the data setting switch or An output selection switch that selects the output of the signal processing section; and a D/A converter that is connected to the output end of the output selection switch and outputs an analog signal; A digital signal processing circuit, characterized in that a selection switch is connected to the signal processing section, and the voltage of the variable voltage source is adjusted by changing it in the same direction, upward or downward.