JPS6241504Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to an autoslice circuit for reliably extracting a digital signal contained in an input signal by varying the slice level in accordance with level fluctuations of the input signal.

BACKGROUND ART Examples of systems for transmitting digital signal waveforms in analog form include teletext broadcasting. Teletext multiplexing is a method in which character signals (including graphics) are multiplexed onto multiple lines during the vertical retrace period of a television signal and transmitted as packets. In this system, the character signals that are received are sequentially written into a memory, and the contents of this memory are read out in synchronization with the horizontal and vertical deflection cycles to be displayed on a television receiver. This character signal is multiplexed onto, for example, the 18th line and the 20th line, and a 296-bit character signal CS, for example, is sent following the horizontal synchronization signal HS and color burst signal CB. It is stipulated in Therefore, on the receiving side, a character signal represented by a digital signal is extracted by extracting and slicing a predetermined line signal based on the vertical synchronization signal VS, and this character signal is processed at a predetermined period. It is captured by sampling.

However, since television signals are sent via broadcast waves, their levels often fluctuate due to disturbances. As a result,
There is a problem in that the level of the character signal multiplexed with the television signal and sent varies, and an erroneous signal is generated from the slicing circuit that slices the input signal at a fixed level.

DISCLOSURE OF THE INVENTION Accordingly, an object of the present invention is to provide an autoslice circuit that can reliably extract a digital signal contained in an input signal without being affected by level fluctuations of the input signal.

In order to achieve such an object, the present invention detects the rising and falling parts of the input signal by differentiating the input signal and extracting positive and negative slice outputs of the differentiated output signal,
By setting the flip-flop circuit by the rising edge of the positive slice output of the differential output signal and resetting the flip-flop circuit by the falling edge of the negative slice output of the differential output signal, the digital signal contained in the input signal is output from the flip-flop circuit. This is to extract the .

In the autoslice circuit configured in this way, the digital signal is extracted by detecting the rising and falling edges of the input signal and controlling the set and reset of the flip-flop circuit. The digital signal contained in the input signal can be reliably extracted without being influenced by the input signal.

BEST MODE FOR CARRYING OUT THE INVENTION FIG. 1 is a circuit diagram showing an embodiment of an autoslice circuit according to the present invention. In the figure, 1 is a differentiator circuit that differentiates a video signal A as an input signal supplied to an input terminal 2, and is an operational amplifier circuit 1.
a, a capacitor 1b, and a resistor 1c. 3 is a first circuit for slicing and outputting the positive polarity portion of the differential signal B generated from the differentiating circuit 1;
It is a slice circuit, and the power supply + is connected through the resistor 3a.
A variable resistor 3b is connected between V and ground to generate a reference value Vr ₁ , and generates an "H" level output during the period when the differential signal B exceeds the reference value Vr ₁ . and a comparator 3c. Reference numeral 4 denotes a second slice circuit that slices and outputs the negative polarity portion of the differential signal B generated from the differential circuit 1, and is connected between the power supply +V and the ground via a resistor 4a, so that the reference value is
It is composed of a variable resistor 4b that generates Vr ₂ and a comparator 4c that generates an "L" output when the differential signal B falls beyond the reference value Vr ₂ . 5 is an inverter that inverts the output signal c of the first slice circuit 3; 6 is a buffer amplifier that amplifies the output signal of the second slice circuit 4; 6 is a flip-flop circuit which is set by the output of the inverter 5; , a digital output DO is generated from the set output terminal Q by being reset by the output signal of the buffer amplifier 6.

In the autoslice circuit configured in this way, the horizontal synchronizing signal shown in Fig. 2a is input to the input terminal 2.
HS, color burst signal CB and character signal CS
When a video signal A comprising: in this case,
The center level of the differential signal B is always constant without being affected by level fluctuations of the input video signal A. In this case, the positive part of the differential output B indicates the rising part of the video signal A, and the negative part indicates the falling part of the video signal A. The positive polarity of the differential signal B generated in this manner is extracted in the first slice circuit 3. In other words, the variable resistor 3b of the first slice circuit 3 receives the differential signal B as shown by the dotted line in FIG. 2b.
A predetermined reference voltage located at the positive part of the
Vr ₁ is occurring. And this reference voltage Vr ₁
is compared with the differential signal B in the comparator 3c, and the output signal C becomes "H" only during the period when the differential signal B exceeds this reference value _Vr1 , as shown in Figure 2c. occurs in Also variable resistor 4
b generates a predetermined reference voltage Vr ₂ located at the negative pole portion of the differential signal B, as shown by the dotted line in FIG. 2b. This reference voltage Vr ₂ is compared with the differential signal B in the comparator 4c, so that the output signal D is set to the second level only during the period in which the differential signal B exceeds the reference value Vr ₁ and decreases It is generated as shown in Figure d. The output signal C generated in this manner indicates the rising portion of the video signal A, and the output signal D indicates the falling portion of the video signal A, as in the case described above.

Next, the output signal C is inverted in the inverter 5 and then sets the flip-flop circuit 6.
The output signal D resets the flip-flop circuit 6 via the buffer amplifier 6. Therefore, the set output terminal Q of the flip-flop circuit 6 outputs the digital output signal DO shown in FIG. will be done.

In a circuit configured like this,
By differentiating the video signal, slice processing is performed after converting the signal into a differentiated signal whose reference level does not change with respect to level fluctuations, so that level fluctuations in the video signal do not affect the slice output. Then, the signals divided into two by differentiation are integrated again in the flip-flop circuit 6 to generate the digital signal DO.
It will be output as

As explained above, the auto-slice circuit with the above configuration can perform slice processing without being affected by input signal level fluctuations, so it can always accurately process digital signals regardless of input signal level fluctuations. It can be taken out.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of an autoslice circuit according to the present invention, and FIGS. 2a to 2e are operation waveform diagrams of various parts of the circuit shown in FIG. 1. 1... Differential circuit, 3, 4... First and second slice circuits, 5... Inverter, 6... Buffer amplifier, 6... Flip-flop circuit.

Claims (1)

[Scope of utility model registration request] a differentiating circuit for differentiating an input signal; a first slicing circuit for slicing and extracting a positive polarity portion of a differential output signal generated from the differentiating circuit; and a second slicing circuit for slicing and extracting a negative polarity portion of the differential signal; An autoslice circuit comprising a flip-flop circuit that generates a digital signal by being set by the output signal of the first slice circuit and reset by the output signal of the second slice circuit.