JPH0518315B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a separation circuit for separating a data signal superimposed on a video signal.

Conventional configuration and its problems In recent years, various data signals are superimposed on video signals and transmitted, and the signals are used as various control signals, or information different from the video signal is transmitted. things are being done. For example, VHD
In this type of video disc, a data signal related to the video signal is superimposed on a part of the vertical retrace interval, and this data signal is processed separately in addition to the video signal processing. Performs various controls for the player.

Hereinafter, an example of a conventional separation circuit for a data signal superimposed on a video signal will be explained with reference to the drawings.

FIG. 1 shows a block diagram of a conventional separation circuit for separating a data signal superimposed on a video signal. In Figure 1, 1 is an input terminal into which a video signal is input, 2 is a clamp circuit for clamping the pedestal of the input video signal to the voltage generated by voltage source 3, and 4 is the voltage generated by voltage source 3 as a standard. 5 is a circuit that generates a threshold voltage for separating the data signal, and 5 is a circuit that generates a data signal from the clamp circuit 2 and a threshold voltage generation circuit 4.
This is a voltage comparator that compares the voltage from the This voltage comparator 5 converts the data signal superimposed on the video signal, which is an analog signal, into a digital signal that can be processed by the digital signal processing circuit 6.

The operation of the circuit configured as described above for separating data signals superimposed on video signals will be described below. FIG. 2a shows an example of a data signal superimposed on a video signal, where the data signal is set to have an amplitude of 75 IRE with respect to the amplitude of the video signal. For the data signal set in this way,
An example of the most preferred threshold level is 37.5 IRE, which is half the level of 75 IRE. The output waveform of the voltage comparator 5 at this time is shown in FIG. 2b. here,
By setting the threshold value optimally, a signal with a duty ratio of 1:1 is obtained, and the waveform of the transmitted data signal is obtained correctly.

By the way, in such a conventional example, it was necessary to adjust the voltage of the threshold voltage generation circuit 4 to be optimal according to the amplitude of the input signal to the terminal 1. However, since the voltage of the threshold voltage generation circuit 4 is fixed, there is a drawback that when the amplitude of the signal input to the terminal 1 changes, the threshold value deviates from the most desirable level. Generally, the data signal superimposed on the video signal is band-limited to the band determined by the highest frequency of the video signal, and
The waveform and amplitude are distorted because they are subjected to various distortions in the transmission path. It is known that when separating data signals that have been distorted during transmission, if the threshold voltage for separation deviates from the optimal value, errors may occur in the separated signals. There is.

Furthermore, the data separation circuit having the configuration shown in FIG. 1 has a serious drawback in that when the amplitude of the input signal becomes, for example, less than half, it becomes impossible to separate data at all.

Therefore, it is necessary to develop a circuit that automatically sets the threshold value optimally in a circuit that separates the data signal superimposed on the video signal, and also maintains the threshold value constantly at the optimal value even if the amplitude of the input video signal fluctuates. It was wanted.

OBJECT OF THE INVENTION The present invention has been made in view of the above-mentioned prior art, and the present invention automatically sets the optimal threshold value when separating a data signal superimposed on a video signal, and also adjusts the amplitude of the input video signal. The present invention provides a separation circuit for a data signal superimposed on a video signal, which constantly maintains an optimal threshold value even when the video signal is superimposed on the video signal.

Structure of the Invention In order to achieve this object, the separating circuit for the data signal superimposed on the video signal of the present invention includes means for clamping the sync chip of the video signal to a first voltage, and a voltage same as that of the pedestal of the video signal. means for generating a third voltage from the first and second voltages, and means for comparing the data signal superimposed on the video signal and the third voltage to separate the data. ing. The third voltage generated by this configuration varies depending on the amplitude of the input video signal, and the voltage comparison level of the voltage comparator is constantly maintained at an optimum value for the data signal.

DESCRIPTION OF EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings.

FIG. 3 shows a block diagram of a circuit for separating a data signal superimposed on a video signal in one embodiment of the present invention.

10 is an input terminal for a data signal superimposed on a video signal, 11 is a sync chip clamp circuit that clamps the sync chip of the input signal to the first voltage from the voltage source 12, 12 is a voltage source, and 13 is an input terminal for the input signal. A circuit that samples and holds the voltage of the pedestal and generates a second voltage; 14 is a circuit that generates a third voltage, a threshold voltage, based on the voltage from the 12 voltage sources and the 13 sample-and-hold circuit; 15 is a voltage comparator which compares the signal input from the sync chip clamp circuit 11 with the voltage from the threshold voltage generation circuit 14 and outputs a digital signal; 16 is the output terminal of the voltage comparator.

The operation of the circuit configured as described above for separating data signals superimposed on video signals will be described below. The signal input to the input terminal 10 is connected to the voltage source 1 in the sink chip clamp circuit 11.
The sink chip is clamped to a first voltage generated at 2. Sample and hold circuit 1
3 samples and holds the pedestal voltage of the signal clamped by the sync chip clamp circuit 11 to generate a second voltage equal to the pedestal voltage. Next, the operation of the threshold voltage generation circuit 14 and the relationship between the first and second voltages will be explained using FIG. 4. In the same figure, the amplitude of the synchronization signal is A ₁ ,
Let the amplitude of the data signal be A ₂ and the optimal threshold value be A ₃ .
When the aforementioned first and second voltages are respectively V ₁ and V ₂ , the relationship between A ₁ , A ₂ , A ₃ and V ₁ , V ₂ is as shown in FIG. Here, if the output voltage of the threshold voltage generation circuit 14 that generates the third voltage is V _S , then
The threshold voltage generation circuit 14 operates so that the relationships between V ₁ , V ₂ , A ₁ , A ₂ , A ₃ and _VS are as shown in FIG.

The threshold voltage V _S at this time can be expressed using V ₁ , V ₂ , A ₁ , and A ₃ as shown in the following equation.

V _S = V ₂ + (V ₂ − V ₁ )×A ₃ /A ₁ (1) This means that the threshold voltage generation circuit ₁₄
It can be said that this is a circuit that inputs V ₂ , performs the calculation shown in equation (1), and outputs V _S found by equation (1) as the third voltage, which is the threshold voltage. In addition,
The relationship between A ₁ , A ₂ , and A ₃ is a generally defined relationship; for example, in the case of VHD system, A ₁ = 40IRE, A ₂ =
75 IRE, A ₃ = 37.5 IRE. Voltage comparator 15
is the third voltage (=
V _S ) and the voltage from the sync chip clamp circuit 11, and outputs a signal in a format that can be processed by the subsequent digital signal processing circuit.

Now, consider the case where a video signal of arbitrary amplitude is input. In equation (1), A ₁ and A ₃ are fixed constants, and V ₁ is a value determined by the voltage source 12, so each has a constant value. On the other hand, V ₂ changes according to the amplitude of the input signal, and therefore V _S also changes according to the amplitude of the input signal. Now, by transforming equation (1), we obtain equation (2).

V _S −V ₂ /V ₂ −V ₁ =A ₃ /A ₁ (2) Here, since A ₁ and A ₃ are constant values, the left side of equation (2) always becomes a constant value. This is the fourth
As is clear from the figure, this means that the threshold value determined by V _S is always the optimum value for an input signal of any amplitude. Furthermore, this means that even if the amplitude of the input signal changes, the threshold value is constantly maintained at the optimal value.

Next, FIG. 5 shows a specific circuit example of the threshold voltage generation circuit 14. The example in FIG. 5 shows a case where the calculation shown in equation (1) is performed using an operational amplifier. A first voltage V ₁ from the voltage source 12 is input to the terminal 21 . Resistor 23 connects terminal 21 and operational amplifier 20
is connected between the inverting input terminal of terminal 2
2 is the voltage V ₂ from the sample hold circuit 13.
is input and connected to the non-inverting input terminal of the operational amplifier 20. A resistor 24 is connected between the inverting input terminal and the output terminal of the operational amplifier 20.
The terminal 25 is connected to the output terminal of the operational amplifier 20, and this terminal 25 supplies the voltage to the voltage comparator 15.
Outputs V _S. Here, the values of resistors 23 and 24 are
If R ₂₃ , R ₂₄ , then V ₁ , V ₂ ,
The relationship between V _S is expressed as V _S =V ₂ −(V ₁ −V ₂ )×R ₂₄ /R ₂₃ V ₂ +(V ₂ −V ₁ )×R ₂₄ /R ₂₃ (3). This formula corresponds to the case where A ₃ /A ₁ =R ₂₄ /R ₂₃ (4) in formula (1).

The embodiment shown in FIG. 5 has the following advantages, particularly when implemented in an integrated circuit.

The first point is that an operational amplifier circuit with good characteristics can be easily realized on an integrated circuit. The second point is that it is easy to realize the relative ratio of resistance values between resistors with high precision on an integrated circuit, and therefore the ratio of the resistance values of resistors 23 and 24 can be expressed as the relationship shown in equation (4). can be easily set.

Effects of the Invention As described above, the present invention clamps the sync chip of the video signal to the first voltage, generates the same second voltage as the pedestal of the clamped video signal,
A threshold voltage with a value determined by equation (1) is obtained from the first and second voltages, and this threshold voltage is compared with the voltage of the data signal in the input video signal to determine the data signal superimposed on the video signal. By separating, data can be separated by setting the optimal threshold voltage for any input signal amplitude, and even if the input signal amplitude fluctuates, the threshold is automatically set optimally, and its practical effect is There is something big.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a conventional separation circuit for a data signal superimposed on a video signal, Fig. 2 is a diagram showing an example of a data signal superimposed on a video signal and a data signal separated therefrom, and Fig. 3 is a diagram showing an example of a data signal superimposed on a video signal and a data signal separated therefrom. A block diagram of a data signal separation circuit in one embodiment of the present invention,
FIG. 4 is a waveform diagram showing the operation of the embodiment of the present invention, and FIG. 5 is a circuit diagram showing a part of a specific example of the embodiment of the present invention. 11...Sync chip clamp circuit, 12...
Voltage source, 13...sample and hold circuit,
14... Threshold voltage generation circuit, 15... Voltage comparator, 20... Operational amplifier, 23, 24... Resistor.

Claims (1)

[Scope of Claims] 1. A means for clamping a sync chip of a video signal to a first fixed voltage; sample and hold means for generating a second voltage; and means for generating a third voltage from the first and second voltages;
A separating circuit for a data signal superimposed on a video signal, the circuit having means for comparing a data signal included in the video signal with a third voltage. 2. The means for generating the third voltage is
One end of a first resistor is connected to the resistor and the inverting input, a first voltage is supplied to the other end of the first resistor, a second resistor is connected between the inverting input and the output terminal, and the second resistor is connected between the inverting input and the output terminal. a second voltage is supplied to the inverting input;
2. The data signal separation circuit according to claim 1, comprising an operational amplifier that generates the third voltage from its output terminal.