JPS60245383A - Separating circuit of data signal - Google Patents

Abstract

PURPOSE:To always hold an optimum threshold value even if the amplitude of an input signal is varied by generating the voltage of a roughly middle amplitude of a data signal superposed on a video signal, using it as a threshold value, to separate a data. CONSTITUTION:A signal inputted to an input terminal 10 is clamped to the first voltage V1 generated by a voltage source 12 in a sink chip clamping circuit 11. An S/H circuit 13 sample-holds a pedestal voltage of said clamped signal and generates the second voltage V2 equal to the pedestal voltage. When the amplitude of a synchronizing signal, the amplitude of a data signal, and an optimum threshold value are denoted as A1, A2 and A3, respectively, and an output voltage Vs from a threshold voltage generating circuit 14 is derived, the output voltage Vs goes to as shown by an expression. In such a way, even if an input video signal is varied, V2 is varied in accordance with said variation, by which Vs is also varied, therefore, an optimum voltage is always held.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention 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 have been superimposed on video signals and transmitted.
The signals are used as various control signals or to transmit information different from the video signal. For example, on a VHD video disc,
A data signal related to the video signal is superimposed on a part of the vertical blanking interval, and various controls of the ship layer can be performed by separately processing this data signal in addition to processing the video signal. I am doing it.

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 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. , a circuit that generates a threshold voltage for separating data signals; 5, 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 6 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 a data signal set in this manner, an example of the most preferred threshold level is 37.5 IRE, which is half the level of 75 IRH. The output waveform of the voltage comparator 5 at this time is shown in FIG. 2(b). 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, the voltage of the threshold voltage generation circuit 4 is adjusted to the amplitude of the input signal to the terminal 1,
I had to adjust it to be optimal. However, since the voltage of the threshold voltage generating circuit 4 is fixed, there is a drawback that if the amplitude of the signal input to the terminal 1 changes, the threshold value deviates from the lightest 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 its waveform and amplitude are distorted due to various distortions in the transmission path. . When separating such data signals that have been distorted during transmission, it is known that 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 desirable 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 rare.

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 eliminates fluctuations in 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 separation circuit for the data signal superimposed on the video signal of the present invention includes a means for clamping the sync tip of the video signal to a first voltage, and a means for clamping the sync tip of the video signal to a first voltage, and a circuit that is the same as the pedestal of the video signal. Consisting of means for generating a voltage, 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. has been done. The third voltage generated by this configuration varies depending on the amplitude of the input video signal, so that the voltage comparison level of the voltage comparator is constantly maintained at an optimal value for the data signal.

DESCRIPTION OF EMBODIMENTS An 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.

1o is an input terminal for a data signal superimposed on a video signal;
11 connects the input signal sink chip to the first one from the voltage source 12.
Sync tip clamp circuit that clamps to the voltage of 12
1 is a voltage source; 13 is a circuit that samples and holds the pedestal voltage in the input signal to generate a second voltage;
4 is a circuit that generates a threshold voltage, which is the third voltage, based on the voltage from the voltage source 12 and the sample-and-hold circuit 13, and 16 is a signal input from the sync chip clamp circuit 11 and the threshold voltage 14. A voltage comparator which compares the voltages from the generation circuit and outputs a digital signal; 16 indicates an 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 1o is clamped to the first voltage generated by the voltage source 12 in the sync tip clamp circuit 11. The sample-and-hold circuit 13 samples and holds the pedestal voltage of the signal clamped by the 11 sync tip clamp circuits, and generates a second voltage equal to the pedestal voltage. Next, the operation of the threshold voltage generation circuit 14 and the first.
The relationship between the second voltages will be explained using FIG. 4. In the figure, the amplitude of the synchronization signal is A1. Set the amplitude of the data signal to A2
．． Let A3 be the optimal threshold value.

The above-mentioned first and second voltages are respectively 1. If it is v2,
A1. A2. The relationship between A3, Vl, and V2(7) is as shown in FIG. Here, if the output voltage of the threshold voltage generation circuit 14 that generates the third voltage is vs, then 1. v2
and A1. A2. The threshold voltage generation circuit 14 operates so that the relationship between A3 and vs becomes as shown in FIG.

The threshold voltage vs at the time of conversion is Vl, V2. A1. When expressed using A3, it is as follows.

Regarding Jin, the threshold voltage generation circuit 14 is a circuit that inputs vl and ■2, performs the calculation shown in equation 0), and outputs the whole vs in equation (1) as the third voltage, the threshold voltage. I can say that there is. In addition, A1゜A2. The relationship A3 is a generally defined relationship; for example, in the case of VHD system, A1=4oIRE, A2--rts IRE, A
3=37.5 IRE. The voltage comparator 16 compares the third voltage (=V3) thus generated with the voltage from the sync tip 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), A1 and A3 are fixed constants, and vl is a value determined by the voltage source 12, so each has a constant value. On the other hand, v2 changes according to the amplitude of the input signal, and therefore VB also changes according to the amplitude of the input signal. Now, by transforming equation (1), equation (2) is obtained.

Here, since A1 and A3 are constant values, the left side of equation (2) always becomes a constant value. This means that, as is clear from FIG. 4, the dark value rounded by vs 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 optimum value.

Next, FIG. 5 shows a specific circuit example of the threshold voltage generation circuit 14. The example in FIG. 6 shows a case where the calculation shown in equation (1) is performed using an operational amplifier. Voltage source 1 is connected to terminal 21.
The first voltage 1 from 2 is input. Resistor 23 is connected between terminal 21 and the inverting input terminal of operational amplifier 200. Sample and hold circuit 1 is connected to terminal 22.
The voltage 2 from 3 is input and connected to the non-inverting input terminal of the operational amplifier 20. Resistor 24 is operational amplifier 2o
is connected between the inverting input terminal and output terminal of.

The terminal 26 is connected to the output terminal of the operational amplifier circuit 2o, and this terminal 26 outputs the voltage Vs to the voltage comparator 15. Here, if the values of the resistors 23 and 24 are each R23 and R24, then in the circuit of FIG. 6, ■1°v2. The relationship between vs is expressed as ゛. This equation corresponds to the case in equation (1).

The embodiment shown in FIG. 6 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 accuracy on an integrated circuit.
Therefore, the ratio of the resistance values of the resistors 23 and 24 can be easily set to the relationship shown in equation (4).

Effects of the Invention As described above, the present invention provides a first sync chip for video signals.
, generate a second voltage that is the same as the pedestal of the clamped video signal, obtain a threshold voltage of a value expressed by equation (1) from the first and second voltages, and calculate this threshold voltage. By comparing the voltage of the data signal in the input video signal and separating the data signal superimposed on the video signal, data can be separated by setting the optimal threshold voltage for any input signal amplitude. In addition, even if the amplitude of the input signal fluctuates, the threshold value is automatically set to an optimal value, which has a great practical effect.

[Brief explanation of drawings]

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 block diagram of a conventional separation circuit for a data signal superimposed on a video signal. 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. 6 shows a part of a specific example of the embodiment of the present invention. FIG. 11...-sync tip clamp circuit, 12...
Voltage source, 13 ・Sample and hold circuit, 14-
m-Threshold voltage generation circuit, 15...Voltage comparator, 2
o...Operation amplifier, 23.24...Resistor. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 Figure 4

Claims (2)

[Claims] (1) means for clamping the sync tip of the video signal to a first voltage, means for generating a second voltage equal to the voltage of the pedestal of the clamped video signal, and a means for generating a second voltage from the first and second voltages; A separation circuit for a data signal superimposed on a video signal, comprising means for generating a third voltage and means for comparing the third voltage with a data signal included in the video signal. (2) The means for generating the third voltage is configured such that one end of the first resistor is connected to the first and second resistors and the inverting input, and the 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 a second resistor is connected to the non-inverting input.
2. The data signal separation circuit according to claim 1, comprising an operational amplifier to which a third voltage is supplied and which generates a third voltage from its output terminal.