JPS5836553B2 - Channel Skipping Warehouse - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an automatic channel selection device for a television receiver.
The present invention relates to a channel skip signal forming circuit for skipping unnecessary channels and selecting only regular channels.

Conventionally, as a device for receiving only authorized channels, a plurality of protrusions are installed on a disc fixed to the rotary shaft of the tuner, and a leaf switch is installed near this disc, and the leaf switch is activated by the protrusions. A device is used in which the switch can be closed, and the electrical signal generated by closing the switch is used as a detection signal indicating either a normal channel or an unnecessary channel.

Such a device has the disadvantage that the position of the protrusion must be changed depending on the channel arrangement in each region.

Therefore, in order to electrically discriminate between normal channels and unnecessary channels, it is conceivable to detect the presence or absence of a video intermediate frequency signal or a synchronization signal to form a channel skip signal.

However, the method of simply detecting the presence or absence of a synchronization signal or video intermediate frequency signal may cause a malfunction in determining a regular channel and an adjacent channel.

The transmission characteristics of television radio waves are 6M as shown in Figure 1.
For channels ABCDE in the Hz band, broadcast waves are present on every other channel, for example, A, C, and E channels, and B and D channels are adjacent channels.

When the regular channel A is selected, the video intermediate frequency amplifier operates with a passing characteristic of 1A as shown by the broken line.

However, for example, when adjacent channel D is selected, almost no television radio waves are received, so the receiver's AG
Due to the function of the C circuit, the gain of the video intensifier becomes extremely high, and as shown by -CID in Figure 1, the pass characteristic is broadened, and a part of it extends to the band of the regular channel C or E, and the gain of the video intensifier becomes extremely high. Alternatively, the Takagi component of the E video signal is mainly extracted.

In this way, in adjacent channel D (the same applies to B), even the video signal of the regular channel is extracted, so it may lead to malfunction to distinguish between the regular channel and the adjacent channel simply by the presence or absence of the video intermediate frequency signal or synchronization signal. was there.

The present invention takes the above points into consideration and forms a channel skip signal electrically, but eliminates the possibility of malfunction in adjacent channels.

Hereinafter, one embodiment of the present invention will be described with reference to FIGS. 2 to 4.

In FIG. 2, 2 is a final stage transistor of a video intermediate frequency amplifier, 3 is, for example, a positive polarity video detector, 4 is a video amplifier, and 5 is a cathode ray tube.

The output of the video detector 3 is also supplied to the audio intermediate frequency amplifier 6, and the 4.5 MHz audio intermediate frequency signal from the audio intermediate frequency amplifier 6 is demodulated by the FM demodulator 7 to produce an audio signal. This audio signal is amplified by an amplifier 8 and supplied to a speaker 9.

Further, although not shown, an AGC detector is provided in association with the video detector 3, and the video intermediate frequency amplifier includes a peak value type AG
C is applied, and its peak value is held constant.

A first detection circuit, such as an integrating circuit 10, for detecting the average level of the video signal from the video detector 3 is provided.

Further, a second detection circuit for detecting the presence or absence of an audio intermediate frequency signal, such as a peak value detection circuit 11 to which the output of the FM demodulator 7 is supplied, is provided.

The output voltages of the integrating circuit 10 and the peak value detection circuit 11 are mixed through resistors 12 and 13, respectively, and this mixed output is applied to the gate of an N-channel FET 14.

The drain output of this FET 14 is supplied to the base of an NPN transistor 15.

The collector of the transistor 15 is connected to a power supply terminal +OO via a resistor 16, and is also led out as an output terminal 17 for a channel skip signal.

A DC voltage obtained by dividing the power supply voltage is applied to the emitter of the transistor 15 by a resistor 18 and a resistor 19, which are sufficiently smaller than the resistor 16.

This DC voltage is, for example, 5■, which is the transistor 15
It remains constant regardless of whether it is on or off.

A reference voltage obtained by dividing this DC voltage by resistors 20 and 21 is applied to the source of FET 14.

In the configuration of the embodiment of the present invention described above, when a regular channel is selected, a video intermediate frequency signal Sv shown in FIG. 3 appears on the video detector 3.

The level at the tip of the synchronization signal of this video intermediate frequency signal Sv, that is, the peak value ■P, is kept constant by the peak value type AGC,
Therefore, the peak value of the video signal Sv obtained at the output of the video detector 3 is also constant.

In addition, since the average level (DC component of the waveform) of the video signal Sv2 appearing at the output of the integrating circuit 10 has the peak value Vp ← Yes2, it varies from the lowest ■1 to the highest ■ according to the brightness of the video content. It changes within a level range of 2.

In this example, as shown in FIG. 4, the maximum average level of the video signal Sv mentioned above is set to a level slightly higher than 2 as the reference level.
.

and applied to the source of FET14.

Next, when an adjacent channel is selected, a part of the video signal of the regular channel will be generated as the output of the video detector 3 due to the function of the AGC circuit as described at the beginning, but the video signal at this time Since the waveform has a reduced low-frequency component, the amplitudes of the synchronization signal and video signal are compressed and the rising and falling edges of the waveform are emphasized, as shown by Sv in FIG.

Since the peak value of the video signal occurring in such an adjacent channel is also assumed to be constant vP, the average level ■3 is the reference level ■.

Become bigger.

Incidentally, when an empty channel that is not adjacent to a regular channel and has no broadcast waves is selected, the output level of the integrating circuit 10 is naturally smaller than ■≧.

Therefore, the output voltage of the integrating circuit 10 is at the reference level ■.

If it is small, it can be determined that it is an adjacent channel, but if it is small, it cannot be determined whether it is an empty channel or a regular channel.

This determination is made using the output of the peak value detection circuit 11.

In other words, when selecting a regular channel or an adjacent channel, the audio signal is detected, but the level of the detection output at this time is equal to the detection output generated by detecting the large level limiter noise that occurs when selecting an empty channel. It is small in comparison.

As described above, when a regular channel is selected, the output voltages of the integrating circuit 10 and the peak value detection circuit 11 are both at the reference level ■.

Therefore, the drain current of FET 14 does not flow, its drain potential becomes high, and transistor 15 is turned on.

At this time, the potential of the output terminal 17 is the emitter potential of the transistor 15, for example, 5■.

Next, when selecting an adjacent channel, the output voltage of the integrating circuit 10 becomes higher than the reference level, and when selecting an empty channel, the output voltage of the peak value detection circuit 11 becomes higher than the reference level, and in both cases, The drain potential of FET 14 decreases and transistor 15 is cut off.

At this time, the potential of the output terminal 17 is equal to the power supply voltage, for example, 18
It becomes V.

This is a skip signal, and when this occurs, the selected channel is not maintained and is controlled to be skipped.

Further, the channel selection state is maintained by the voltage of 5.5 cm which is generated when the channel is a regular channel.

According to the present invention described above, since a regular channel is not determined simply by the presence or absence of a video intermediate frequency signal or a synchronization signal, it is possible to eliminate the possibility of a malfunction in which an adjacent channel is determined to be a regular channel.

Furthermore, if you want to skip even if it is a regular channel, if you shift the local oscillation frequency to a higher side by fine tuning, the low frequency component will decrease and the same phenomenon as that of the adjacent channel will occur, and the skip will be performed.

Furthermore, it is possible to generate a skip signal by determining the levels of the audio and video signals that will be put to practical use and selecting the values of the resistors 12 and 13 accordingly.

For example, if you can see an image but the audio is too weak to listen to, you can skip that channel.

FIG. 5 shows the main part of another embodiment of the present invention.

The output voltage of the peak value detection circuit 11 to which the audio signal is supplied from the terminal 22S is supplied to the base of an emitter follower type NPN transistor 23.
Similar to the output voltage of the peak value detection circuit shown in FIG. 2, the emitter output voltage of the normal and adjacent channels is smaller than that of the empty channel, and is several volts in the empty channel.

That is, when receiving the regular channel and the adjacent channel, the signal applied to the terminal 22S is the audio intermediate frequency signal F.
Since it is an audio signal obtained by M demodulation, the amplitude is smaller and the frequency is lower than the signal SS4 when selecting an empty channel, which will be described later, as shown in signals SS2 and SS3 shown in FIG. 6A.

Therefore, when these signals SS2 and SS3 are subjected to peak detection, since they have small amplitudes and consist of low frequency components, the efficiency of peak detection is low and the detection output is small.

On the other hand, when an empty channel is selected, the circuit system operates at maximum gain due to the action of the AGC circuit, so that the noise component is amplified and supplied to the FM demodulator 7 in a large amplitude state.

This FM demodulator 7 generates an output signal according to the frequency shift of the input signal with respect to the center frequency, so if the input signal is noise having a wide band frequency component, the demodulated output is proportional to the frequency dispersion of the input signal. becomes so-called triangular noise, and the demodulated output from the FM demodulator 7 is the signal S shown in FIG. 6A.
It consists of a large amplitude and wideband frequency component like S4.

When this signal SS4 is subjected to peak detection, since this signal SS4 has a large amplitude and consists of frequency components in a high band, a detection output of a sufficiently large level can be obtained.

Further, a video signal obtained by negative polarity detection by the video detector 3 is supplied from a terminal 22V to an integrating circuit 10, and the output voltage of this integrating circuit 10 is divided by resistors 24 and 25 to form an NPN signal.
is supplied to the base of a type transistor 26.

Therefore, in normal channels and empty channels, terminal 2
The signals supplied to the 2V voltage are the signals S' and Sb shown in FIG.

', the transistor 26 is turned on, and the collector potential of the transistor 26 becomes 0. Meanwhile, in the adjacent channel, the signal supplied to the terminal 22V is
The signal Sv3' shown in FIG.

', the transistor 26 turns off, and the collector potential of the transistor 26 becomes the power supply potential, for example, 18V.
becomes.

This collector output voltage is determined by the integrator circuit 10 in FIG.
It will be similar to.

The emitter output voltage of transistor 23 and the collector output voltage of transistor 26 are mixed together via resistors 27 and 28, respectively, and supplied to the base of NPN transistor 29.

Further, the emitter of transistor 29 is grounded.

During normal channel reception, the emitter potential of transistor 23 is low and transistor 26 is on, so the emitter voltage of transistor 23 is further divided by resistors 27 and 28, and the voltage supplied to the base of transistor 29 is becomes very small and transistor 29 is turned off.

Note that the voltage generated at the emitter of the transistor 23 by the audio signal of the broadcast wave when receiving a regular channel is much smaller (for example, 1■ or less) than the voltage generated by noise when receiving an empty channel, so it is set at the reference level ■.

If we appropriately select the difference between ′ and the maximum average level ■2′, we get
This voltage does not turn on the transistor 29.

Next, when receiving adjacent channels, the transistor 23 is off, but the transistor 26 is turned off, so the collector voltage of the transistor 26 rises to the power supply voltage, and this is supplied to the base of the transistor 29 via the resistor 28, so the transistor 29 is turned on.

Furthermore, when receiving an empty channel, the emitter voltage of the transistor 23 becomes very high (for example, several square meters), so even if the transistor 26 is on at this time, the transistor 29 is turned on.
can be turned on sufficiently.

Further, the collector output of the transistor 29 is applied to the base of an NPN transistor 30 whose emitter is grounded, and the collector of the transistor 30 is led out as the skip signal output terminal 17.

At the output terminal 17, a signal inverted from the collector output of the transistor 29, that is, a signal of 0 is generated in the normal channel, and a skip signal of the power supply voltage, eg, 18 V, is generated in the empty channel and the adjacent channel.

[Brief explanation of the drawing]

FIG. 1 is a characteristic diagram used to explain the present invention, FIG. 2 is a connection diagram of an embodiment of the present invention, FIGS. 3 and 4 are waveform diagrams used to explain the same, and FIG. The connection diagram of the embodiment shown in FIG. 6 is a diagram for explaining FIG. 5. 2 is the final stage transistor of the video intermediate frequency amplifier, 3 is the video detector, 6 is the audio intermediate frequency amplifier, 7 is the FM demodulator, 10 is the integration circuit, 11 is the peak value detection circuit, and 17 is the output. It is a terminal.

Claims (1)

[Claims] 1. Detecting a video intermediate frequency signal in which the level of the tip of the synchronization signal is clamped to obtain a video signal in which the level of the synchronization signal is clamped to a first value, and supplying the video signal to an average level detection circuit. , the audio intermediate frequency signal is FM demodulated and then supplied to a peak detection circuit, and the output of the average level detection circuit is on the black level side than the range of values that the average level of the video signal can take when receiving the regular channel, and the first is larger than a second value which is on the white level side than the value of , and when the output of the peak detection circuit is larger than a predetermined value, it is determined that the channel is not a regular channel and a channel skip signal is formed. Channel skip signal forming circuit.