JPS62231574A - Channel switching decision circuit - Google Patents

Abstract

PURPOSE:To improve the reliablity in terms of switching a channel by providing a comparator circuit that compares the number of pulses in the 1st and 2nd counters and outputs them when they approximately coincide with each other and a latch circuit sampling the presence or adsence of a coincidence output from the comparator circuit at every predetermined number of pulses. CONSTITUTION:A reference signal generator circuit 4 outputs a pulse with a fixed period as figure shows, and the 2nd counter 5 counts the pulse. Simultaneously the 1st counter 3 counts a synchronizing signal that a synchronous separator circuit 2 separates from a video signal as figure (a) shows. The comparator circuit 6 compares the values counted by the 1st and 2nd counters 3 and 5, and outputs appear and are transmitted to a latch circuit 7 while said counted values are the same. If a channel is switched in a time (x) in figure (a), a vertical synchronizing signal turns out to be a discontinuous pulse. Then the values counted by the 1st and 2nd counters 3 and 5 become unequal, and the output of the comparator circuit 6 disappears as figure (a) illustrates. Therefore the output of the latch circuit 7 is inverted at the time of sampling the eighth pulse after latching is made before, and the circuit decides that the channel is switched.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a channel switching determination circuit for determining that a channel has been switched in a TV receiver capable of receiving single character broadcasting.

"Prior Art" When receiving a teletext broadcast on a certain channel, for example, channel 1, when switching to another channel, for example, channel 4, the teletext broadcast on channel 1 may be output.

In such cases, traditionally.

It was determined whether the channel had been changed based on the channel signal of the remote control, etc.

``Problems to be solved by the invention'' There were not many problems when the teletext receiver was integrated with the TV receiver, but when the teletext receiver was an adapter type, it was not possible to judge channel switching. Or, even if it were possible, there was a problem that the reliability of operation was low.

"Means for Solving the Problems" The present invention was made to solve the above problems, and includes a sync separation circuit that separates a sync signal from a TV video signal, and a sync separation circuit that separates a sync signal from a TV video signal. a first counter that counts the number of synchronization signals; and a base l having the same period as the synchronization signal.
A base that outputs a pulse signal? A second counter that counts the reference pulse signal outputted from the reference signal generation circuit and the reference signal generation circuit, and a comparison device that outputs an output when the pulses and numbers of the first and second counters are substantially matched. The device includes a circuit and a latch circuit that samples the presence or absence of a coincidence output from the comparison circuit every fixed number of pulses, and the channel switching is determined based on the presence or absence of the output of the latch circuit.

"Operation" Separates, for example, the vertical synchronization signal from the TV video signal,
Count with the first counter. Furthermore, the second counter counts reference pulse signals having the same period as the vertical synchronization signal. If the first and second counters count synchronously, matching signals will always be output from the comparison circuit. However, when the TV synchronization signal becomes discontinuous due to channel switching,
The counts of the first and second counters no longer match. The pulses are sampled every fixed number of pulses, and when they become discontinuous due to mismatch, the output of the latch circuit changes, and it is determined that the channel has been switched.

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

(1) is a video signal input terminal from a TV receiver, and this input terminal (1) is connected to the first signal via a synchronization separation circuit (2) that separates a composite, vertical or horizontal synchronization signal in the video signal.
The clock input terminal of the counter (3) is coupled to the clock input terminal of the counter (3). Further, (4) is a reference signal generation circuit that generates a reference pulse signal, and when the output of the synchronization separation circuit (2) is a vertical synchronization signal, a pulse having the same period as this is outputted.

This reference signal generation circuit (4) is coupled to a clock input terminal of a second counter (5).
) and said first counter (3) are coupled to a comparison circuit (6), said comparison circuit (6) and said second counter (5)
is coupled to the launch circuit (7), and this latch circuit (7)
is coupled to the output terminal (8). The second counter (5) is connected to the clear input terminal of the first counter (3) via an inverter (9), and always starts counting in synchronization with every fixed number of pulses. There is.

Next, the operation using the above configuration will be explained. The reference signal generating circuit (4) outputs pulses with a constant period as shown in FIG. 2(b), and these pulses are counted by a second counter (5). At the same time, the synchronization signal as shown in FIG. 2(a) separated from the video signal by the synchronization separation circuit (2) is also
The first counter (3) counts. These first and second
The count values of the counters (3) and (5) are compared in the comparator circuit (6), and while they match, the output is output and sent to the latch circuit (7). For example, the eighth pulse signal of the second counter (5) is input to the latch circuit (7) as a sampling pulse, and it is determined whether there is a matching output.

If the channel is not switched, the vertical synchronization signal in the video signal will be input with continuous pulses of a constant period, so the comparator circuit (6) will sample the rescue power and stiffness every 8 pulses. It is determined that there is no channel switching.

When the channel is switched at time (x) in FIG. 2(,), the vertical synchronizing signal becomes a discontinuous pulse. Then, the counted values of the first and second counters (3) and (5) do not match, and the output of the comparator circuit (6) disappears as shown in Figure 2 (c), so the 8 pulses after the previous latching At the time of sampling (Y), the output of the latch circuit (7) is inverted, and it is determined that the channel has been switched.

In the embodiment described above, the comparator circuit (6) outputs when the output pulse numbers of the first and second counters (3) and (5) completely match. However, if this is done, there is a risk that even one Neushals signal will be judged as a channel change, so the comparator circuit (6) should be configured to output to the latch circuit (7) even if there is a difference of, for example, two. ,3
It may be determined that the channel has been switched when there is a difference of 1 or more.

In the embodiment described above, the determination is made by sampling every 8 pulses, but the present invention is not limited to this.

"Effects of the Invention" Since the present invention is configured as described above, even if the 5-character broadcast receiver is an adapter type, it operates as if it were an integrated type with the TV receiver (N machine), so it has good operability and is easy to install. This also greatly improves operational reliability.

40 Description of Drawings Fig. 1 is a block diagram showing an embodiment of the channel switching determination circuit according to the present invention, and Fig. 2 is an output waveform diagram of each part.6 (1)...Video signal input Terminal, (2)...Synchronization separation circuit, (3)...First counter, (4)...Reference signal generation circuit, (5)...Second counter, (6)
... Comparison circuit, (7) ... Latch circuit, (8) ...
・Output terminal, (9)...Inverter.

Claims (1)

[Claims] (1) A sync separation circuit that separates a sync signal from a TV video signal, a first counter that counts the number of sync signals separated by this sync separation circuit, and outputs a reference pulse signal with the same period as the sync signal. a reference signal generating circuit that counts the reference pulse signals outputted from the reference signal generating circuit; a second counter that counts the reference pulse signals output from the reference signal generating circuit; circuit and
A channel switching determination circuit comprising: a latch circuit that samples the presence or absence of a matching output from the comparison circuit at every fixed number of pulses; and a channel switching determination circuit, comprising: a latch circuit that samples the presence or absence of a matching output from the comparison circuit at every fixed number of pulses;