JPH0750583A - A/d converter - Google Patents

Abstract

PURPOSE:To always apply the quantizing resolution of an A/D converter at its maximum. CONSTITUTION:The amplitude of the signal taken out of the digital output of an A/D converter 10 is compared with a prescribed level so that the differential data is obtained. The reference voltage Vr is variably set to decide an analog input dynamic range of the converter 10 based on the differential data. Thus the difference between the input dynamic range of the converter 10 and the amplitude range of an analog input signal can always be minimized regardless of the characteristic variance. Therefore the A/D converting operation is always carried out in the maximum input dynamic range of the converter 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an A / D converter, and further to an A / D converter for converting an analog voltage into a binary coded digital value.
The present invention relates to a technology effectively applied to a D converter,
For example, the present invention relates to a technique effectively used for video signal processing such as PinP (picture-in-picture).

[0002]

2. Description of the Related Art For example, some recent television receivers and VTRs (video tape recorders) have a function of inserting a sub-screen into a main screen, that is, a so-called PinP function. The processing for realizing the function is performed digitally. Therefore, for example, an A / D converter is indispensable in the video equipment having the PinP function.

In an A / D converter used for video signal processing or the like, the reference voltage is finely divided and each divided voltage is compared with the analog input voltage, and the comparison result is a digital value of a binary code. Encoding to.

At this time, the analog input dynamic range of the A / D converter is determined by the reference voltage.

That is, as shown in FIG. 8, the highest reference voltage Vrt corresponding to the maximum value "111111" of the digital output becomes the highest value of the analog input voltage and the lowest value corresponding to the lowest value "000000" of the digital output. The reference voltage Vrb becomes the minimum value of the analog input voltage. The analog input dynamic range extends from the highest voltage Vrt to the lowest voltage Vrb, and the analog voltage input within this dynamic range is converted into a digital value (see, for example, Japanese Patent Laid-Open No. 63-157522).

[0006]

However, the present inventors have clarified that the above-mentioned technique has the following problems.

That is, in the above-mentioned A / D converter, the amplitude range of the analog input signal such as the video signal must not exceed the dynamic range defined by the reference voltage. This is because if the amplitude range of the analog input signal exceeds the dynamic range, the waveform information of the protruding portion will be lost from the digital output (A3).

However, if the amplitude range of the analog input signal is too smaller than the above dynamic range, this time,
The width of change in the digital output value converted from the analog input signal becomes narrow, and the quantization resolution of the signal decreases (A1).

In order not to lose the waveform information and not to impair the resolution, it is necessary to set the amplitude range of the analog input signal by the AGC (automatic gain control) or the like so that the amplitude range substantially matches the dynamic range (see FIG. A
2).

However, the amplitude range of the analog input signal is not always constant due to the characteristic variation or characteristic variation of the circuit on the signal source side. Even if the amplitude range of the analog input signal could be made uniform, A /
Characteristic variations may occur on the D converter side.

Therefore, it is necessary to wait a sufficient margin between the amplitude range of the analog input signal and the input dynamic range of the A / D converter in consideration of the above variation. That is, the analog input dynamic range of the A / D converter had to be set with a margin so as to be sufficiently wider than the amplitude range of the analog input signal. As a result, the substantial quantization resolution of the A / D converter is lowered, which becomes a major impediment to the improvement of image quality in video signal processing such as PinP.

As described above, in the conventional A / D converter,
There is a problem that the originally provided quantization resolution is not fully utilized.

It is an object of the present invention to provide a technique which allows the quantization resolution of the A / D converter to be always utilized to the maximum extent.

The above and other objects and features of the present invention will be apparent from the description of the present specification and the accompanying drawings.

[0015]

Among the inventions disclosed in the present application, a brief description will be given to the outline of typical ones.
It is as follows.

That is, the reference voltage that determines the analog input dynamic range of the A / D conversion circuit by the difference data obtained by comparing the amplitude value of the signal output from the digital output of the A / D conversion circuit with a predetermined set value. Is to variably set.

[0017]

According to the above-mentioned means, the difference between the input dynamic range of the AD converter and the amplitude range of the analog input signal can always be minimized regardless of the characteristic variation and characteristic variation. Therefore, the conversion operation from analog to digital is always performed by fully using the input dynamic range of the A / D converter.

This achieves the object that the quantization resolution of the A / D converter can always be maximized.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described below with reference to the drawings.

In the figures, the same reference numerals indicate the same or corresponding parts.

FIG. 1 shows an embodiment of an A / D converter to which the technique of the present invention is applied. 10 is an A / D converter circuit, Ain is an analog input signal, and Dout is a digital output signal. , 11 is a signal extraction circuit for extracting only a specific amplitude reference signal included in the digital output signal Dout, 1
Reference numeral 2 is an amplitude detection circuit for detecting the amplitude value of the extracted amplitude reference signal, 13 is a digital comparator for comparing the detected amplitude value with a predetermined set value and outputting difference data thereof, and 14 is for decoding the difference data. The decoder 15 is a reference voltage variable circuit that variably sets the reference voltage Vr of the A / D converter 10 according to the value of the difference data that has been tegged.

Here, the analog input dynamic range of the A / D converter 10 is set by the reference voltage Vr supplied from the reference voltage variable circuit 15.

FIG. 2 partially shows details of the A / D conversion circuit 10 and the reference voltage variable circuit 15.

As shown in the figure, the A / D conversion circuit 10
Is a voltage dividing resistor array 101, a comparator array 102, an encoder 1
03, etc., the reference voltage Vr (Vrt-Vrb) given from the reference voltage variable circuit 15 is finely divided, each divided voltage is compared with the analog input voltage, and the comparison result is binary coded. Digital value of "(00
0000-111111 ") and outputs.

The reference voltage variable circuit 15 has analog switch trains 151 and 152, voltage dividing resistor trains 153 and 154, voltage follower amplifiers 155 and 156, and the like, and the reference voltage that is variably set by the decode output of the difference data. Vr (Vrt, Vrb) is output.

In this case, as the reference voltage Vr, two kinds of the highest reference voltage Vrt and the lowest reference voltage Vrb are output. That is, the highest-order reference voltage Vr corresponding to the maximum digital output value “111111” of the A / D conversion circuit 10
t and the lowest reference voltage Vrb corresponding to the minimum digital output value “000000” of the A / D conversion circuit 10 are output and given to the A / D conversion circuit 10.

In FIGS. 1 and 2, the analog input signal Ain is digitally converted by the A / D conversion circuit 10 and output. At this time, the analog input signal Ai
If n is a color video signal, for example, the above A /
The digital output signal Dout of the D conversion circuit 10 includes a specific amplitude reference signal whose amplitude is predetermined, such as a color burst signal. The specific amplitude reference signal is extracted by the signal extraction circuit 11, and the amplitude value of the amplitude reference signal is further detected by the amplitude detection circuit 1.
Detected by 2. The detected amplitude value is the comparator 13
Is compared with a predetermined set value, and after the difference data obtained by this comparison is decoded by the decoder 14,
It is given to the reference voltage variable circuit 15 as control data.

As a result, the reference voltage Vr that determines the input dynamic range of the A / D conversion circuit 10 is variably controlled so that the amplitude value of the amplitude reference signal becomes a predetermined value.
That is, a control loop that minimizes the difference between the input dynamic range of the AD conversion circuit 10 and the amplitude range of the analog input signal is formed. With this control loop, the analog-to-digital conversion operation is always performed by using the input dynamic range of the A / D conversion circuit 10 to the maximum regardless of the characteristic variations and characteristic variations. Therefore, the quantization resolution of the A / D conversion circuit 10 is always maximized.

FIG. 3 shows a second embodiment of an A / D converter to which the technique of the present invention is applied.

The A / D converter shown in the figure is configured for digital conversion of a color video signal including a color difference signal and a color burst signal.

In the figure, the signal extracting circuit 11 is constructed by using a burst extracting circuit 31, and extracts a color burst signal contained in the digital output signal Dout.

The amplitude detection circuit 12 is constructed by using an arithmetic circuit 32, and as shown in FIG. 4, color difference signals Xb, Yb (BY axis component values, RY) detected in a color burst section.
The color burst signal amplitude value before demodulation is obtained by vector-calculating the combined value Zb of the axial component value). The reference voltage Vr that determines the input dynamic range of the A / D conversion circuit 10 is variably set based on the difference data value between the color burst signal amplitude value and the set value.

As a result, the resolution of the A / D conversion circuit 10 can be utilized to the maximum extent, and this can greatly contribute to the improvement of the quality of reproduced images, especially the accuracy of color reproduction.

FIG. 5 shows a third embodiment of an A / D converter to which the technique of the present invention is applied.

The A / D converter shown in the figure is also configured to digitally convert a color video signal including a color difference signal and a color burst signal, like the one shown in FIG. The example further includes an averaging unit 33 that averages the difference data value between the color burst signal amplitude value and the set value.

The averaging device 33 sequentially averages the difference data value between the color burst signal amplitude value and the set value every N times the period of horizontal synchronization (N is an integer of 1 or more). By this averaging process on the time series, the influence of noise superimposed on the analog input signal Ain, quantization noise in the A / D conversion circuit 10, etc. is reduced, and the reference voltage of the A / D conversion circuit 10 is reduced. It is possible to prevent the Vr from changing unnecessarily.

In the illustrated example, the averaging process is performed after the decoder 14, but the decoder 14
Before the amplitude detection circuit 12, or at a plurality of locations.

FIG. 6 shows a fourth embodiment of an A / D converter to which the technique of the present invention is applied.

In the A / D converter shown in the figure, a signal presence / absence detection circuit 34 for detecting whether or not a specific amplitude reference signal such as a color burst signal is present in the digital output signal Dout, and a fixed voltage. A fixed reference voltage generation circuit 36 that outputs Vs and a switch circuit 35 that switches and selects the reference voltage Vr / Vs applied to the A / D conversion circuit 10 are added.

Thus, for example, the reference voltage of the A / D conversion circuit 10 is changed when the color signal is input, and the reference voltage is fixed when the luminance signal is input, depending on the type of the input signal. Therefore, optimum A / D conversion processing can be performed.

FIG. 7 shows a fifth embodiment of an A / D converter to which the technique of the present invention is applied.

In the A / D converter shown in the figure, the analog input signal Ain of the A / D conversion circuit 10 is converted into Ain1 and Ain.
A switch circuit 37 for switching and selecting from two signal sources of 2 and a signal extraction circuit 1 corresponding to the two signal sources.
1A, 11B, amplitude detection circuits 12A, 12B, comparator 1
3A, 13B, decoders 14A, 14B, averaging unit 33
Two systems of A and 33B are provided. Each system independently has a set value for obtaining difference data. Further, there is provided a switch circuit 37 for selectively selecting the difference data value detected for each system and giving it to the reference voltage variable circuit 15.

That is, when the first signal source Ain1 is selected as the analog input signal Ain of the A / D conversion circuit 10, the signal extraction circuit 11A of the first system, the amplitude detection circuit 12A, the comparator 13A, and the decoder 14A. , Averaging unit 3
By the control loop using 3A, the input dynamic range of the A / D conversion circuit 10 can be optimized and set. When the second signal source Ain2 is selected, the signal extraction circuit 11B of the second system, the amplitude detection circuit 12B,
The input dynamic range of the A / D conversion circuit 10 can be optimized and set by a control loop using the comparator 13B, the decoder 14B, and the averaging device 33A.

As a result, the conditions for variably setting the reference voltage Vr can be set independently, for example, at the time of inputting a color signal and at the time of inputting a luminance signal. A / D conversion processing can be performed.

Although the invention made by the present inventor has been specifically described based on the embodiments, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the invention. Needless to say. For example, the signal extraction circuit 11 and the amplitude detection circuit 12 may be peak value detection circuits depending on the type of analog input signal.

In the above description, the case where the invention made by the present inventor is mainly applied to the A / D conversion processing of a color image signal which is the field of application which is the background of the invention has been described, but the invention is not limited to this. Instead, it can be applied to, for example, A / D conversion processing of audio signals or digital processing of radio signals, so-called A / D conversion processing by DSP.

[0047]

The effects of the typical ones of the inventions disclosed in this application will be briefly described as follows.

That is, it is possible to obtain the effect that the quantization resolution of the A / D converter can be always maximized.

[Brief description of drawings]

FIG. 1 is a first A / D converter to which the technique of the present invention is applied.
Circuit diagram showing an example

FIG. 2 is a circuit diagram showing details of an A / D conversion circuit and a reference voltage variable circuit.

FIG. 3 is a second A / D converter to which the technique of the present invention is applied.
Figure showing an example of

FIG. 4 is a graph showing a color difference signal included in a color video signal.

FIG. 5 is a third A / D converter to which the technique of the present invention is applied.
Figure showing an example of

FIG. 6 is a fourth A / D converter to which the technique of the present invention is applied.
Figure showing an example of

FIG. 7 is a fifth A / D converter to which the technique of the present invention is applied.
Figure showing an example of

FIG. 8 is a diagram showing a relationship between a reference voltage and an input / output value of the A / D converter.

[Explanation of symbols]

 10 A / D conversion circuit Ain analog input signal Dout digital output signal Vr reference voltage 11 signal extraction circuit 12 amplitude detection circuit 13 digital comparator 14 decoder 15 reference voltage variable circuit 33 averaging device

Claims (7)

[Claims] 1. A comparison means for comparing an amplitude value of a signal output from a digital output signal of an A / D conversion circuit with a predetermined set value and outputting difference data thereof, and an analog input dynamic of the A / D conversion circuit. An A / D converter comprising a reference voltage varying means for variably setting a reference voltage defining a range according to the value of the difference data. 2. A means for extracting a specific amplitude reference signal from a digital output signal of the A / D conversion circuit, wherein the reference voltage of the A / D conversion circuit is varied based on the amplitude value of the extracted amplitude reference signal. The A / D converter according to claim 1, wherein the A / D converter is set. 3. The A / D converter according to claim 1, further comprising means for averaging data for variably setting the reference voltage of the A / D conversion circuit in time series. 4. A means for extracting a specific amplitude reference signal from a digital output signal of an A / D conversion circuit, a means for detecting the presence or absence of the amplitude reference signal, and the A / D when there is no amplitude reference signal. 4. A / D converter according to claim 1, further comprising means for switching a reference voltage of the converter to a fixed voltage. 5. The A / D converter according to claim 1, wherein differential data for variably setting the reference voltage of the A / D conversion circuit is created for each type of input signal. 6. The reference voltage varying means sets the highest reference voltage corresponding to the maximum digital output value of the A / D conversion circuit and the lowest reference voltage corresponding to the minimum digital output value of the A / D conversion circuit. The A / D converter according to claim 1, wherein the A / D converter is configured to output. 7. A color burst signal which is a reference signal of a color signal is demodulated, a first component indicated by the demodulated color burst signal is Xb, a second component is Yb, and a color burst signal before demodulation When the amplitude is Zb, 1 /
A processing apparatus having means for obtaining Zb by 2Zb ² = Xb ² + Yb ² .