JPH0522436B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a waveform equivalent circuit for correcting low-band group delay of an input video signal in the vicinity of 1.5 MHz in a teletext receiver.

``Prior Art'' A teletext signal is extracted from the vertical retrace period of a received video signal, but if there is a group delay in the broadcast station signal, the number of error bits increases. Broadcasting station side too
Care has been taken to ensure that delays of 200nsec or more do not occur; in reality, delays of up to ±100nsec are a problem.

However, conventional teletext receivers have used transversal filters to correct this group delay. This process used a digital filter to process the input teletext signal and mix it with the original teletext signal, using at least 10 stages of filters.

``Problems to be solved by the invention'' Conventional transversal filters are effective in countering ghosts, but the circuit configuration is extremely complex because more than 10 stages of filters must be combined to correct group delay. There was a problem that adjustment was troublesome and expensive.

An object of the present invention is to obtain a circuit that operates inexpensively and reliably by using an equivalent machine consisting of a delay line.

"Means for Solving the Problems" The present invention provides a teletext receiver in which teletext data is extracted from a received video signal by an acquisition circuit 6 via a waveform equivalent circuit 3 and outputted. Equivalent circuit 3 has a delay time of +
Three equivalent machines 4a, 4 consisting of delay lines with three different stages of 100nsec, 0nsec, -100nsec
b, 4 and these three equivalent machines 4a, 4b, 4c
The selector 5 is connected to the input circuit 6, the error correction circuit 8, and the fieldback system of the controller 9, and selects one of the teletext data input by the acquisition circuit 6. A waveform equivalent circuit for a teletext receiver, characterized in that an error correction circuit 8 detects the number of error bits from the output, and a controller 9 outputs a selector switching signal based on the detection signal of the error correction circuit 8. be.

"Operation" First, teletext data is extracted from the received video signal via, for example, a delay-free equalizer 4b.
The extracted data is processed by the error correction circuit 8 to correct the error rate,
For example, detecting the number of error bits per packet,
This error bit number data is sent to the controller 9. The controller 9 outputs a switching signal from the controller 9 based on the error bit number data, and the selector 5 selects the three equalizers 4a, 4b, 4c.
Choose one. Equivalent machine 4a, 4b,
4c is composed of delay lines having different delay times, and the selector 5 selects one that reduces the number of error bits. In this way, the group delay is corrected by constantly detecting and feeding back the number of error bits.

"Example" Hereinafter, one example of the present invention will be described based on the drawings.

Reference numeral 1 denotes a video signal input terminal, and this input terminal 1 is connected to a waveform equivalent circuit 3 via a buffer circuit 2. This waveform equivalent circuit 3 is composed of equalizers 4a, 4b, and 4c having three different delay times, and a selector 5 for selecting them. Specifically, the equivalent machines 4a, 4b, 4c are +
It consists of delay lines of 100nsec, 0nsec, and -100nsec.

A capture circuit 6 for capturing teletext signals is coupled to the output side of the selector 5, and an output terminal 7 is provided on the output side of the capture circuit 6, and a controller 9 is connected via an error correction circuit 8.
This controller 9 is coupled to the selector 5.

In the circuit configuration as described above, a video signal input to the input terminal 1 is sent to the waveform equivalent circuit 3. Assuming that the teletext data is initially sent to the capture circuit 6 via the 0 nsec equivalent device 4b, the teletext data is captured by the capture circuit 6 and output from the output terminal 7. At the same time, the error correction circuit 8 detects the error rate of teletext data, for example, the number of error bits per packet, and sends it to the controller 9. This controller 9 outputs a switching signal corresponding to the number of error bits to switch and control the select 5. In selection 5, an equivalent machine that reduces the number of error bits is selected. Similarly, the number of error bits is constantly detected and fed back to correct the group delay.

"Effects of the Invention" (a) As mentioned above, the present invention has a delay time of +100nsec,
Since it has three equivalent filters 4a, 4b, and 4c with three different stages of 0nsec and -100nsec, and a delay line, compared to conventional transversal filters with more than 10 stages, Costs can be drastically reduced.

(b) It is possible to constantly detect the number of error bits and feed it back to reliably correct group delay.

[Brief explanation of the drawing]

The figure is a block diagram showing an embodiment of a waveform equivalent circuit of a teletext receiver according to the present invention. 1...Input terminal, 2...Buffer circuit, 3...
Waveform equivalent circuit, 4a, 4b, 4c...Equivalent machine (delay line), 5...Selector, 6...Intake circuit, 7...Output terminal, 8...Error correction circuit, 9
……controller.

Claims (1)

[Claims] 1. In a teletext receiver in which teletext data is extracted and output from a received video signal by an acquisition circuit 6 via a waveform equivalent circuit 3, the waveform equivalent circuit 3 has a delay time of +100 nsec,
Three equivalent machines 4a, 4b, 4c consisting of delay lines with three different stages of 0nsec and -100nsec
and a selector 5 for selecting one of these three equivalent machines 4a, 4b, and 4c, and this selector 5 is coupled to the feedback system of the acquisition circuit 6, error correction circuit 8, and controller 9, An error correction circuit 8 detects the number of error bits from the output of the teletext data taken in by the acquisition circuit 6, and a selector switching signal is output from the controller 9 based on the detection signal of the error correction circuit 8. Waveform equivalent circuit of a teletext receiver featuring