JPH0294814A - A/d converter - Google Patents

Abstract

PURPOSE:To reduce noise by inputting the same analog signal to excess A/D converters, summing their digital outputs and dividing the result by the number of added signals when analog signals less than number of the A/D converters in a digital TV in which plural number of the A/D converters are employed. CONSTITUTION:An analog switch 7 is provided, which switches an SVHS C signal also to an input composite video signal of an A/D converter 4. Outputs of two A/D converters 3, 4 are added by an adder 8 and the result is divided by 2 at a multiplier 10. In order to halve the gain, the multiplier 10 is to be shifted by one bit. Thus, analog noise caused at the MSB change point is halved and the nose is divided into two and outputted with a timewise deviation. That is, the level of the analog noise generated at the MSB change point is decreased and scattered timewise.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to an A/D (analog/digital) converter for a television receiver (hereinafter referred to as digital TV) that performs digital signal processing. Regarding.

(Prior Art) Current digital TVs are designed to have high image quality. Therefore, as shown in Figure 4, there is often an input terminal 2 for 5VHS C signal, and in that case, an A/D input terminal for 5VHS C signal manually.
A converter 4 is provided. Furthermore, these digital TVs may be designed to be multi-functional and include an A/D converter for sub-screen video signals in addition to the A/D converter for the main screen. In addition, in such a digital TV, the composite video and 5VHS Y signal common input terminal 1 is connected to the A/D converter 3 for composite video and 5VH3 Y signals, and the composite video and 5VHS of this A/D converter 3 are connected to the Y signal input terminal 1. A digital data output terminal 5 of the Y signal is connected to a digital signal processing circuit. The digital data output terminal 6 for the 5VHS C signal of the A/D converter 4 is connected to a digital signal processing circuit.However, when only the main screen is displayed by inputting a composite video signal, this main screen composite video signal Nothing other than the A/D converter is used.

On the other hand, when a digital TV video signal is a digital signal, there is no S/N deterioration due to the mixing of peripheral noise and thermal noise of each active element. Therefore, S/N deterioration due to the above-mentioned noise mixture in digital TV is limited to before A/D conversion and after D/A conversion. In particular, the introduction of noise from digital circuits or the like before A/D conversion has an adverse effect on the Y/C separation of the composite video signal, and is not limited to mere S/N deterioration. Furthermore, when a video signal is A/D converted, it inevitably generates quantization noise.

(Problem to be solved by the invention +8) The present invention was made in view of the fact that the conventional technology suffers from S/N deterioration. An object of the present invention is to provide an A/D converter that can improve the overall image quality of a digital TV by improving the resolution of the converter.

[Structure of the invention] (Means and effects for solving the problem) The present invention provides a digital TV having several A/D converters, in which fewer analog signals than the number of A/D converters are input. In this case, the same analog signal is input to the remaining A/D converters. Then, the A/
Add the digital outputs of the D converters and then divide by the added number.

Then, if there is no correlation between the noise generated by each A/D converter, the noise at the output will be 1/(number of A/D converters)
becomes.

(Example) Next, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows an embodiment of the present invention, and the same parts in FIG. 1 as in FIG. 4 are given the same reference numerals. That is, the analog switch 7 is connected so that the input of the A/D converter 4 for the C signal of 5VIIS can also be switched to the composite video signal input terminal 1.
will be established. An adder 8, a selector 9, and a multiplier 10 are provided to add the outputs of the two A/D converters 3.4 and divide by 2. In this case, the multiplier 10 reduces the gain to 1/2
To do this, you only need to shift one bit. The output obtained from 9 bits may be used as is, or only the upper 8 bits may be supplied to the next digital signal processing circuit.

When a 5VHS signal is input to the circuit shown in FIG. 1, the switch 7 is connected to the input terminal 2 side and the circuit operates at the fourth
It will be exactly the same as the figure.

Next, consider noise generated within the A/D converter. First, switching noise in which the MSB changes can be considered. In other words, the digital data is all 1-0 or O-1 after this point.
and changes. Then, sudden changes in the output digital data may cause noise to be mixed into the input analog data via the power supply.

Therefore, with switch 7 connected to input terminal 1 side,
Slightly shift the DC components of the signals that enter the input terminals of the D converter 3 and A/D converter 4, or slightly shift the upper and lower limits of the dynamic range of the A/D converter 3 and A/D converter 4. A DC offset is applied to the outputs of the two A/D converters. Then, the point at which the MSB changes as described above causes a time lag in the A/D converter 3 and the A/D converter 4. Then, the analog noise generated at each MSB change point is halved and divided into two parts with a time lag, which are then output. In other words, the analog noise generated at the MSB change point is lowered in level and dispersed in time.

In addition, the noise generated in the A/D converter is 1/2 in terms of energy and 1/2 in terms of the voltage output of the obtained digital data for all noises that are uncorrelated between A/D converters 3 and 4. ff--3dl'3.

When Figure 1 is simplified, it becomes as shown in Figure 2. That is, by connecting the input of the selector 9, which was fixed to 0, to the output of the A/D converter 3 itself, the gain of the multiplier 10 can be fixed to 1/2.

In this case, only the analog switch 7, digital adder 8, and selector 9 are required to be added compared to the conventional circuit.

Also, the linearity of A/D converter 3 and A/D converter 4 is
1/2 LSB over the entire dynamic range of the converter
If the error is as follows, set the DC offset between A/D converter 3 and A/D converter 4 to 1/2LS as described above.
By setting it to B, the performance of the output terminal 5 becomes 9 bits, which can be improved by 1 bit. Therefore, even in subsequent digital signal processing circuits, when a composite video signal is input, signal processing can be performed with improved performance of a 1-bit signal. In this case, the only connection required is to provide a 1/2 LSB DC shift circuit 11 between the input terminal 1 of FIG. 2 and the A/D converter 4 as shown in FIG.

Further, the upper and lower limits of the dynamic range of the A/D converter 3 and the A/D converter 4 may be set by simply providing a 1/2 LSB offset between the two.

Incidentally, in the present invention, the A/D converter 4 can be replaced with an A/D converter for a sub-screen of a digital TV equipped with a sub-screen display function. It is also conceivable to further add the output of the sub-screen A/D converter to the output of the adder 8 shown in FIG. 1 to reduce the gain of the multiplier 10 to ⅓.

As described above, the present invention is not limited to the above-mentioned embodiments, and can be implemented with various modifications without departing from the gist thereof.

[Effects of the Invention] As detailed above, according to the present invention, an unused A/D converter can be effectively used with a simple additional circuit, and an A/D
By improving the performance of the converter, the overall image quality of the digital TV can be improved by reducing the amount of noise generated in the A/D converter and improving the resolution of the A/D converter.

[Brief explanation of drawings]

FIG. 1 is a configuration explanatory diagram showing one embodiment of the present invention, FIGS. 2 and 3 are configuration explanatory diagrams showing another embodiment of the present invention in which the circuit in FIG. 1 is simplified, and FIG. FIG. 2 is a configuration explanatory diagram showing a conventional A/D converter. 1... Composite video and 5VHS Y signal common input terminal, 3... Composite video and 5VH3 Y signal A/D converter, 5... Composite video and 5V
H3 Y signal digital data output terminal, 2...5V
Input terminal for H3 C signal, 4...S V II S
A/D converter for the C signal, 6...5VH3 digital data output terminal for the C signal, 7...analog switch,
8... Adder, 9... Selector 10... Multiplier, 11... 1/2 LSB DC shift circuit. Applicant's agent Patent attorney Takehiko Suzue How to handle VJI Figure 1 Figure 2

Claims (1)

[Claims] A switch circuit for distributing the same analog signal to a plurality of A/D converters in a television receiver that performs digital signal processing and has a plurality of built-in A/D converters greater than the number of input analog signals, and this switch. The circuit includes a selector that selects the output of each A/D converter when the same analog signal is input to a plurality of A/D converters, and an adder that adds the outputs selected by the selector. An A/D converter characterized by: