JPS6382188A - Detection circuit - Google Patents

Abstract

PURPOSE:To improve the detection accuracy of correlation between transmission signals by using a transistor(TR) formed adjacently to a semiconductor substrate to decide a DC bias of an input terminal of a comparator to detect the line correlation. CONSTITUTION:A voltage level of 1st and 2nd input terminals of a comparator 14 is clamped on a prescribed voltage level nearly equal to each other and the level of 1st and 2nd transmission signals is compared by a comparator 14 with the clamped voltage level. As a result, even if the level difference of the transmission signal level before one horizontal scanning period is large, since the DC bias of the input terminal of the comparator 14 is decided once by TRs Q1, Q2 and the DC bias between both the terminals is nearly equal and constant, it is detected surely. Thus, the correlation of the transmission signal is detected excellently based on the detection.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a detection circuit suitable for application to various video equipment such as television receivers and video tape recorders (hereinafter referred to as VTRs). In particular, the present invention relates to circuit technology that is effective in separating luminance signals and color signals.

[Conventional technology]

In NTSC television broadcasting, color signals are transmitted superimposed on luminance signals. On the other hand, television receivers and V
The TR is configured to separate the luminance signal Y and color signal C and perform desired signal processing. The above separation is referred to as Y/C separation by those skilled in the art, and will therefore be referred to as Y/C separation below.

"Television Technology J (January issue, 1986, published by Denshi Gijutsu Publishing Co., Ltd., pp. 39-41) describes the relationship between luminance signals and color signals in NTSC VTRs. The color signal C is frequency interpolated into the high frequency range of the signal Y (approximately 2 to 4 MHz range),
A comb filter is used to separate the two.

The inventors of the present invention have studied how to properly perform Y/C separation in order to increase the resolution of images. Although the following is not a publicly known technique, it is a technique studied by the present inventor, and its outline is as follows.

That is, conventionally, Y/C separation has been performed using a band pass filter with a center frequency of 3.58 MHz and a low pass filter with a cutoff frequency of about 3 MHz. However, this separation method has problems, such as a part of the frequency components of the luminance signal Y being mixed into the frequency components of the color signal C, which tends to cause a cross-color phenomenon. Therefore, Y/C separation using a comb filter has been performed using the frequency interpolation, which reduces the cross color phenomenon and improves resolution.

However, the inventor has discovered that the comb filter has the following problems.

[Problem to be Solved by the Invention] In other words, the comb filter has a delay circuit that delays a composite video signal for one horizontal scanning period, and a color filter that subtracts the current composite video signal and the delayed composite video signal. It is composed of a subtraction circuit that obtains a signal C, and an addition circuit that adds up to obtain a luminance signal Y.

In order to obtain the luminance signal Y and color signal C, a correlation (
It is assumed that there is a line correlation (hereinafter referred to as line correlation). However, if the signal levels of the luminance signal Y are significantly different, in other words, if there is no line correlation, the difference in the luminance signal Y will appear in the color signal C, making it impossible to perform good Y/C separation. was revealed by the present inventor.

In view of the advantages and disadvantages of the comb filter, the present inventor performed Y/C separation using a comb filter when there is a line correlation between the current composite video signal and the delayed composite video signal,
When there is no line correlation, Y/
We considered performing C separation.

In this case, the line correlation between the current composite video signal and the delayed composite video signal is detected, and a comb filter and low-pass filter are used.
A detection circuit is required to switch between the bandpass filter and the bandpass filter. For this reason, we are considering supplying the current composite video signal and the delayed composite video signal via a capacitor to the input of a comparator fixed to DC bias using a resistor to obtain a detection signal that detects the presence or absence of line correlation. did. but,
In the above circuit configuration, even if there is a line correlation between the current composite video signal and the delayed video signal, if the direct current (DC) level between the signals one horizontal scanning period ago is significantly different, the capacitor It was found that due to the discharge time constant with the resistor, the DC level of the input to the comparator was different, resulting in an erroneous determination that there was no line correlation. When the above-mentioned erroneous judgment occurs, even though Y/C separation can be performed using a comb filter, a low pass signal is generated.

Y/C separation is performed using a bandpass filter. As a result, image fidelity deteriorates and noise becomes noticeable on the screen.

An object of the present invention is to provide a detection circuit that can satisfactorily detect the correlation between first and second transmission signals.

Other objects of the present invention are television receivers, VTRs,
It is an object of the present invention to provide a line correlation detection circuit for effectively separating a luminance signal Y and a color signal C in video equipment such as the above.

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

[Means for solving problems]

A brief overview of typical inventions disclosed in this application is as follows.

That is, the determination of the DC bias of the input terminal of the comparator for detecting line correlation is performed by a transistor formed close to the semiconductor substrate. A bipolar transistor is applied to this transistor. Transistors formed close to each other on a semiconductor substrate have good correlation, and transistor parameters such as pace-emitter voltages are extremely equal. Specifically, the emitters of transistors whose bases were set to a common reference bias voltage were each connected to two input terminals of the comparator, and a horizontal synchronization signal corresponding to the first information of the transmission signal was supplied. When it operates in the on state, each input terminal is connected to the base voltage from the above reference bias voltage.
Securely maintain the emitter voltage level and perform clamp operation. When the transmitted signal transitions to a luminance signal corresponding to the second information, the transistor is turned off due to an increase in the level of the emitter, and the input terminal of the comparator changes in accordance with the second information of the transmitted signal, and the above-mentioned comparison The structure is such that the correlation between the two can be detected using a device.

[Effect]

According to the above means, the voltage levels of the first and second input terminals of the comparator are clamped to predetermined voltage levels that are substantially equal to each other, and the voltage levels of the first and second input terminals of the comparator are clamped to predetermined voltage levels that are substantially equal to each other, and The comparator then compares the levels of the second transmission signal and the second transmission signal. As a result, even if the level difference between the transmission signal levels one horizontal scanning period ago is large, the DC bias between the two terminals is determined by transistors with good correlation, so the DC bias between both terminals is Since they are substantially equal and constant, they can be detected reliably, and based on this detection, the correlation of the transmitted signals can be detected satisfactorily.

〔Example〕

A first embodiment of a detection circuit to which the present invention is applied will be described with reference to FIGS. 1 to 4. In addition, FIG. 1 is a circuit diagram of a Y/C separation circuit using the above-mentioned detection circuit, and FIGS. 2 and 3 are spectrum diagrams showing the frequency distribution of the composite video signal supplied to the above-mentioned Y/C separation circuit. FIG. 4 shows a waveform diagram explaining the circuit operation of the signal processing circuit.

The feature of this embodiment is that the Y/C separation of the composite video signal is performed well.

First, the circuit operation when there is line correlation will be described. Prior to this, the outline of the composite video signal (hereinafter referred to as video signal 5) Va will be described. As shown in FIGS. 2 and 3, the frequency distribution of the video signal Va is such that the chrominance signal C is centered around the 3.58 MHz wide carrier wave signal in the high frequency portion of the luminance signal Y.
are interpolated, and vb indicates an audio signal.

The switch S1 is switched and controlled by a detection signal Vc, which will be described later. When the switch S1 is switched to the contact a, the video signal Va is switched to the comb filter 1 ["Television Technology J.
(See September 1985, pp. 54-56). In the video signal Va, the phase of the burst signal differs by 180 degrees every horizontal scanning period, and the luminance signal Y has the same phase. When the subtraction circuit 3 subtracts the current video signal Va and the delayed video signal Va' delayed by one horizontal scanning period by the delay circuit 2, the luminance signal Y is erased because it is in phase, and -
A 2C color signal C is obtained.

On the other hand, when the current video signal Va and the delayed video signal Va' are added by the adder circuit 4BC, a 2Y luminance signal Y is obtained, and the color signal is erased. The above color signal C is switch S
, to the color signal processing circuit, and the luminance signal Y
is supplied to the luminance signal processing circuit via switch S.

The most notable circuit operation of this embodiment is that the detection circuit 11V
It is carried out at c.

The first and second filter circuits 12 and 13 are low-pass filters each having a cutoff frequency set to approximately 3 MHz, and are configured to receive a horizontal synchronizing signal vh, which corresponds to the first information in the present invention, and a second It allows luminance signals and the like corresponding to information to pass through.

Since the current video signal Va is supplied to the filter circuit 12, the luminance signal Yz shown in the upper part of FIG. 4 is obtained from the filter circuit 12. On the other hand, since the filter circuit 13 is supplied with the delayed video signal Va', the filter circuit 13 obtains a luminance signal Y1 corresponding to a video signal one horizontal scanning period before the current video signal Va. The luminance signal YI.

Yt is connected to transmission path 1 via coupling capacitors C1, C,
1. I! supplied to

Since the luminance signals Y, , Y, are synchronized by the delay circuit 2, the horizontal synchronizing signal vh causes the transistors Q1 . The emitter voltage of Q2 decreases at the same time,
Both are turned on.

As a result, each emitter voltage of transistors Q, ,Q,
In other words, each input terminal of the comparator 14 is clamped to a voltage level lower than the reference bias voltage V r e f by the base-emitter voltage of the transistor Ql IQ. Since the reference bias voltage Vref is commonly supplied to the transistors Q+ and Qt, no voltage difference occurs between the input terminals of the comparator 14, and the level of the detection signal Vc does not change. Therefore, the switches S to S8 maintain their switching states as shown.

Next, when moving to time point 12, transistor Q+,
Each emitter voltage of Q- increases, but since the bias voltage is fixed, transistors Q+ and Qt are turned off.

After t2, the voltage level of each input terminal of the comparator 14 changes in accordance with the level change of the luminance signals Y, Y, and if no voltage difference occurs, there is no change in the level of the detection signal Vc. The switches S, -S3 maintain the switching states shown. As a result, Y/C separation by the comb filter 1 continues to be performed.

Next, the circuit operation when line correlation disappears will be explained.

When the luminance signal Y of the current video signal Va decreases significantly, the luminance signal obtained from the first filter circuit 12 changes in level from -fY2 to Y3 as shown in the upper part of FIG. 4. on the other hand,
The luminance signal obtained from the second filter circuit 13 is
As shown in the lower part of the figure, although it changes from Y to Y,
There is almost no difference in level. Also, since there is no change in the level of the horizontal synchronizing signal vh, the transistor Q2
．． A clamping operation similar to that described above is performed by Qt, and no voltage difference occurs between the input terminals of the comparator 14.

14, the luminance signal Y3. There is no level difference between the input terminals of the comparator 14, and although the transistors Q, .

Therefore, the level of the detection signal Vc does not change, and the switches 81 to S8 maintain the illustrated switching states.

When moving to time point 11, the luminance signal Y! changes to a high level, but the luminance signal Y3 remains at a low level, and the level difference between the two becomes a dog. That is, a voltage difference occurs between each input terminal of the comparator 14, and the level of the detection signal Vc changes. As a result, the switches S and -S3 are switched all at once from contact point a to contact point a.

The video signal Va that was being supplied to the No. 1 terminal is transferred to the switch S.
The signal is supplied to a band pass filter 21 and a low pass filter 22 via I. The band pass filter 21 is
The center frequency is set to about 3.58MHz, and the color signal C
This is what you get. The color signal C is supplied to the color signal processing circuit via the switch S.

The low-pass filter 22 has a cutoff frequency of 3M.
It is set at about Hz, and a luminance signal Y is obtained. The luminance signal Y is supplied to the luminance signal processing circuit via the switch S.

Next, the circuit operation when the brightness signal Y4 is supplied to the transmission path I and the brightness signal Y3 is supplied to the transmission path I2 will be described.

In this case as well, transistors QI and Q- are turned on in response to horizontal synchronizing signal vh, and each input terminal of comparator 14 is clamped to the above voltage level. And luminance signal Y3. When Y appears, the comparator 14 compares the two, and the level of the detection signal Vc changes, causing the signal to pass from the comb filter 1 to the low-pass filter 21 .Y as described above. Switching to bandpass filter 22 is performed.

Note that the capacitors C, C, are charged by sequentially supplying the luminance signal to the transmission path I++ as described above, but the transistors Qs and Qt are turned off as described above. While the resistance R,,R
, is discharged through. Therefore, fluctuations in the voltage level of the transmission path 11+ due to the charging voltage are reduced, and the transistors Q7. Combined with the clamping effect of Qt,
Undesired level fluctuations at each input terminal of the comparator 14 can be reduced. As a result, the comparator 14 can accurately detect the level difference between the luminance signals.

The detection circuit 11 and the Y/C separation circuit have the following effects.

(1) Supply first and second transmission signals for detecting correlation to a comparator, and connect a transistor whose base is set to a common bias voltage and whose emitter is connected to each input terminal of the comparator. establish. The transistors are operated in response to the level of the transmission signal to set each of the input terminals to a predetermined voltage level based on the reference voltage, and the transistors are inactivated in response to a change in the level of the transmission signal. By detecting the level change using the comparator, each input signal terminal of the north end device is temporarily set to a predetermined reference voltage level before performing the comparison operation, and the correlation of the transmitted signal can be accurately detected. This effect can be obtained.

(2) the first and second transmission signals as a current video signal;
By obtaining the video signal delayed by one horizontal scanning period,
The effect is that the line correlation of the video signal is accurately detected.

(3) According to (2) above, if the video signal has line correlation, perform Y/C separation using a comb filter; if there is no line correlation, perform Y/C separation using a low-pass filter or band-pass filter. This provides the effect of optimal Y/C separation depending on the presence or absence of line correlation in the video signal.

(4) According to (3) above, television receivers, VTRs
It is possible to reduce the noise that appears in the images of video equipment such as, and has the effect of improving the resolution.

Above, the invention made by the present inventor has been specifically explained based on examples, but the present invention is not limited to the above examples, and it is understood that various changes can be made without departing from the gist of the invention. Needless to say.

For example, the adder circuit of the comb filter may be configured to supply a current video signal and a color signal to obtain a summation output. It is also possible to omit the switch S1.

In the above explanation, the invention made by the present inventor was mainly applied to a circuit for detecting the correlation of transmitted signals, which is the background field of application, but the invention is not limited to this, and two By detecting the level difference between signals, the control signal can be widely used in control devices and the like.

〔Effect of the invention〕

A brief description of the effects obtained by typical inventions disclosed in this application is as follows.

That is, first and second transmission signals containing a plurality of information are supplied to the comparator, and the pace is set to a common bias voltage, and the emitter of each transistor is connected to each input terminal of the comparator. and operating the transistor in response to first information of each of the transmission signals to maintain the input terminal at a voltage level based on the bias voltage, and then controlling the difference in second information of the transmission signal. Since the comparator obtains a detection signal corresponding to This has the effect of improving.

[Brief explanation of the drawing]

1 to 4 show a first embodiment of a detection circuit to which the present invention is applied. FIG. 1 is a circuit diagram of the above detection circuit and a Y/C separation circuit using the same, and FIG. is a frequency distribution diagram of the video signal supplied to the Y/C separation circuit, FIG. 3 is an explanatory diagram showing the interpolation relationship between the luminance signal and chrominance signal, and FIG. 4 is a transmission diagram illustrating the circuit operation of the detection circuit. It shows a waveform diagram of a signal.

Claims (1)

[Claims] 1. First and second transmission signals containing a plurality of pieces of information are individually supplied to input terminals, a comparator detects a mutual correlation by comparing the two, and each control terminal is set to a common bias voltage. , each output terminal is individually connected to the input terminal, operates in response to first information included in the first and second transmission signals, and sets the input terminal to a voltage level based on the bias voltage. and first and second transistors, respectively, which are held in position and are rendered inactive in response to the second information to enable the comparator to compare the first and second transmission signals. Characteristic detection circuit.