JPH087745Y2 - PLL synchronous detection system video detection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a PLL synchronous detection type video detection device using a phase locked loop capable of switching between a keyed type and a continuous type.

[Prior Art] A video detection device that detects a video intermediate frequency signal and extracts the video signal is a pseudo video intermediate frequency carrier (pseudo IF) of 58.75 MHz extracted by ringing oscillation of the video intermediate frequency signal.
In place of the pseudo-synchronous detection method in which synchronous detection is performed using (carrier), a so-called PLL synchronous detection method in which product detection is performed using a video intermediate frequency carrier extracted from a video intermediate frequency signal by a phase locked loop is becoming mainstream recently. .

The PLL synchronous detection type video detection device 1 shown in FIG. 3 first removes unnecessary band components from the video intermediate frequency signal sent from the channel selection device (not shown) by the SAW filter 2,
Subsequently, after being subjected to multistage amplification in the video intermediate frequency amplifier circuit 3, it is sent to the synchronous detection circuit 4. The synchronous detection circuit 4 uses a video intermediate frequency carrier (IF carrier) generated by a phase locked loop that performs a phase lock operation only during the horizontal synchronous signal period, and performs synchronous detection by a double balanced mixer or the like. The detected output is sent to a video amplification circuit (not shown) at the next stage via the 4.5 MHz trap circuit 5 for attenuating the audio beat and the output buffer circuit 6.

By the way, the IF carrier generation circuit 7 for generating the video intermediate frequency carrier first uses the video intermediate frequency signal extracted from the subsequent stage of the video intermediate frequency amplifier circuit 3 as a signal of the reference phase.
It is taken into the APC detection circuit 8. The oscillation output of the voltage controlled oscillator 9 is sent to the APC detection circuit 8 through the + 45 ° phase shift circuit 10 so that the phase difference is exactly 90 °, and the video intermediate frequency signal and the 90 ° phase advance oscillation signal are sent. An error voltage corresponding to the phase difference is supplied to the low pass filter circuit 12 via a sample hold circuit 11 described later. The filtered output of the low pass filtering circuit 12 is supplied to the voltage controlled oscillator 9 as a control voltage,
The oscillation frequency and the phase are variably controlled according to the control voltage.

On the other hand, the output of the voltage controlled oscillator 9 is supplied to the synchronous detection circuit 4 as a video intermediate frequency carrier wave via the −45 ° phase shift circuit 13. The −45 ° phase shift circuit 13 is a circuit for confronting the intermediate frequency image signal, which is the input of the synchronous detection circuit 4, with the image intermediate frequency carrier in an opposite phase relationship, and includes the APC detection circuit 8 and the sample hold circuit 11 And the low-pass filtering circuit 12, the voltage-controlled oscillator 9, and the + 45 ° phase shift circuit 10 form a closed loop, so-called phase locked loop (PLL), to maintain the above-mentioned anti-phase relationship, and to detect the video intermediate frequency signal synchronously. The required video intermediate frequency carrier is obtained. For this reason,
In the PLL synchronous detection method, a stable video intermediate frequency carrier with a constant amplitude can be used as a reverse-phase carrier for synchronous detection without being affected by the fluctuation or modulation degree of the video intermediate frequency signal. A sharp detection output can be obtained even for an image in which the signal amplitude greatly changes.

The PLL synchronous detection type video detection device 1 described above has a 4.5 MHz trap circuit 5 in order to quickly pull in the phase locked loop when the power is turned on or the channel is switched.
When the phase lock detection circuit 14 is connected in the subsequent stage and there is no synchronous detection output, the output of the phase lock detection circuit 14 increases the time constant of the low-pass filtering circuit 12 and locks by lowering the loop gain. The range is expanded. However, once the pull-in is completed, the time constant of the low-pass filtering circuit 12 is returned to the normal value and the loop gain is increased to reduce the residual phase error.

Further, in the case of this example, in order to accurately extract the ghost cancellation reference signal from the broadcast signal in which the ghost cancellation reference signal is superimposed in the vertical retrace line period of the television signal such as clear vision broadcasting, in order to accurately extract the horizontal and vertical This is a so-called keyed type configuration in which the phase locked loop is activated only during the synchronization signal period. The reason why the key period is selected as the synchronization signal period is based on the following reasons in addition to the above reasons. That is, for example, when a television radio wave in which a ghost wave indicated by a dotted line is superimposed on a desired liquid indicated by a solid line in FIG. 4 is received, an orthogonal ghost wave having a 90 ° phase difference from that of the desired wave is vector-added, This is because the change in the amplitude of the desired wave is most noticeably likely to cause a change in the detection phase, and such a change in the detection phase is likely to directly hit the voltage controlled oscillator 9 and destabilize its oscillation output. For,
The television signal transmitted by being negatively modulated has the maximum amplitude, and the phase locked loop is activated only in the synchronizing signal period in which the influence of the quadrature ghost wave is minimal. Therefore, the APC detection circuit 8
The sample hold circuit 11 connected to is a circuit for realizing the above-mentioned keyed type operation, and the key pulse generation circuit 15 connected to the output buffer circuit 6 generates a key pulse based on the sync signal separated from the video detection output. Is supplied to the sample and hold circuit 11, and the phase error voltage sent from the APC detection circuit 8 is sampled and held only during this key pulse period.

[Problems to be Solved by the Invention] The conventional PLL synchronous detection type video detection device 1 does not have thorough radio wave management on the broadcast station side like the simple CATV broadcasting, and the carrier frequency of the television radio wave itself. The phase-locked loop that is activated only during the horizontal or vertical sync signal period when a radio wave that fluctuates is received is considered to be due to the true video intermediate frequency carrier wave required for synchronous detection and the sample hold period. The deviation from the video intermediate frequency carrier that is only updated is large, and when it is far from the ideal synchronous detection, noise with an amplitude of about 1.5 times the average amplitude appears in the detection output due to the mismatch of the detection axes, and the image is reproduced. The quality may be significantly reduced.

Therefore, in this example, a manual open / close switch 16 is provided in the middle of the signal line connecting the key pulse generation circuit 15 and the sample hold circuit 11, and if noise is noticeable in the reproduced image, the open / close switch 16 is closed at the user's discretion. And took appropriate measures so that the phase-locked loop can be switched from the keyed type to the continuous type. That is, by closing the open / close switch 16, the sample hold circuit 11
Since the phase error voltage sent from the APC detection circuit 8 is output as it is, the phase locked loop can be switched from the keyed type to the continuous type that constantly monitors the carrier.

However, the operation of the open / close switch 16 is solely left to the user's own judgment, and there is no clear criterion for judgment, and it is unfamiliar to a user who is not particularly interested in the principle of synchronous detection. The situation where you have to manually adjust the image quality by operating the open / close switch 16 may lead to distrust of the product, and the intention of a kind design is rather an ironic result of causing unnecessary confusion for the user. There was a problem that it did not exist.

[Means for Solving the Problems] The present invention is to solve the above problems, and is a PLL synchronous detection system video detection that performs synchronous detection using a video intermediate frequency carrier extracted from a video intermediate frequency signal by a phase locked loop. In the device, the phase locked loop is
An operation mode switching means for switching between two types, a keyed type which is activated only during a synchronization signal period or a continuous type which is always activated, and a signal level of a video detection output are monitored, and this signal level exceeds a preset standard. At this time, the first feature is that the operation mode switching circuit is provided with a monitoring circuit for instructing switching from the keyed type to the continuous type, and instead of the monitoring circuit, each channel is previously selected. The operation mode preset which stores the operation mode set to, reads the operation mode corresponding to the channel selected in response to the channel selection operation, and specifies the keyed type or continuous type operation to the operation mode switching circuit. Second that means is provided
It is a feature of.

[Operation] This invention is a keyed type or always active in which the phase locked loop is activated only during the synchronizing signal period when performing synchronous detection using the image intermediate frequency carrier extracted from the image intermediate frequency signal by the phase locked loop. When the signal level of the video detection output exceeds a certain standard, the keyed type is switched to the continuous type to perform video detection adapted to the quality of the received radio wave.

In addition, the operation mode set for each selected channel is stored in advance, and the operation mode corresponding to the selected channel is read in connection with the channel selection operation.
By designating the keyed type or continuous type operation, the operation mode can be preset for each selected channel.

[Embodiment] Each embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a circuit configuration diagram showing an embodiment of a PLL synchronous detection type video detection device of the present invention.

The PLL synchronous detection type video detection device 21 shown in FIG.
The operation of the sample hold circuit 11 incorporated in the phase locked loop in the F carrier generation circuit 7 is configured to be automatically switched from the keyed type to the continuous type according to the magnitude of the peak detection output of the video detection output. . That is, in the embodiment, the monitor circuit 22 is connected to the output buffer circuit 6, and the output of the monitor circuit 22 automatically switches the open / close switch 16 as the operation mode switching means.

The monitoring circuit 22 compares a peak hold circuit 23 that holds the output peak value of the output buffer circuit 6 and the hold output of this peak hold circuit 23 with a constant reference voltage Er, and when the hold output exceeds the reference voltage Er. The comparison circuit 24 outputs a closing command.

Here, it is assumed that radio waves are not thoroughly controlled on the broadcast station side like simple CATV broadcasting, and that radio waves are received such that the carrier frequency of the television radio waves themselves fluctuates. In this case, since the continuous type phase-locked loop activated only during the horizontal or vertical sync signal period is used, the true video intermediate frequency carrier required for synchronous detection and the video intermediate frequency updated only during the sample hold period. The deviation from the frequency carrier is large, and noise with an amplitude of about 1.5 times the average amplitude appears in the detection output due to the mismatch of the detection axes.

However, at this time, the peak hold circuit in the monitoring circuit 22
Since the output of 23 exceeds the reference voltage Er set in the comparison circuit 24, the open / close switch 16 is closed by receiving the output of the comparison circuit 24, and the phase locked loop is switched from the keyed type to the continuous type. As a result, the monitoring circuit 22 that senses the situation responds without waiting for the user's own judgment, and the phase locked loop is automatically switched from the keyed type to the continuous type, which causes poor radio wave management on the broadcasting station side. It is possible to prevent deterioration of reproduced image quality due to carrier fluctuation due to

However, when receiving regular television signals,
The phase-locked loop returns to the keyed type and protects the keyed type, which is the basic operation, unless the carrier receives a varying electric wave.For example, the ghost cancel reference signal superimposed in the vertical blanking period of the clear vision broadcast signal is accurate. It can be extracted well, and the influence of the phase shift of the detection axis due to the ghost wave superimposed on the desired wave can be minimized.

In the above embodiment, the quality of the received radio wave is monitored by the monitoring circuit 22 operating in real time. However, in the television receiver once set, the radio wave that can be received and its quality are considered to be fixed. Therefore, it is also effective to add a so-called preset function in which opening or closing of the open / close switch 16 is preset for each channel.

Therefore, the PLL synchronous detection type video detection device 3 shown in FIG.
In 1, the abundant control functions of the tuning microcomputer circuit 32 are used so that the operation mode can be preset for each tuning channel, and the tuning channel and phase are locked in the data memory circuit 33 connected to the tuning microcomputer circuit 32. The correspondence of the droop operation modes is stored first. In this case, the channel selection microcomputer circuit 32 that has received the channel selection operation issues a channel selection command corresponding to the specified channel to the channel selection circuit (not shown), and at the same time, the data memory circuit 33 operates in the operation mode. The phase-locked loop can be switched to the keyed type or the continuous type by opening and closing the open / close switch 16 according to the read operation mode.

However, the tuning microcomputer circuit 32 has a manual initial setting as a standard specification. Therefore, the user needs to specify the operation mode for each channel only once at the beginning through the tuning microcomputer circuit 32. However, once the preset is completed, the troublesome work of operating the open / close switch 16 each time the channel selection operation is performed is unnecessary. Therefore, for example, even in the case where the programs of two stations having different operation modes are continuously recorded in the answering machine. , You can leave without worrying about the operation mode switching operation accompanying channel switching.

In addition, the PLL synchronous detection system video detection device 21 and 31 are combined, and the initial setting by the tuning microcomputer circuit 32 is performed by the monitoring circuit 22.
The configuration may be performed by

[Advantage of Device] As described above, the device of the present invention performs the synchronous detection using the video intermediate frequency carrier extracted from the video intermediate frequency signal by the phase locked loop, and the phase locked loop is used only during the sync signal period. Since it is possible to switch between two types, that is, a activated keyed type or a constantly activated continuous type, and when the signal level of the video detection output exceeds a certain standard, the keyed type is switched to the continuous type.
When receiving a good television wave with stable radio wave management of the carrier, the phase-locked loop is operated as a keyed type, so that, for example, from a clear vision broadcast signal, a ghost cancellation reference signal superimposed in the vertical blanking period is generated. It is possible to accurately extract or minimize the influence of the phase shift of the detection axis due to the ghost wave that is superimposed on the desired wave, and conversely, it is a simple type CATV.
As in broadcasting, when the broadcasting station does not have thorough radio wave management and receives a radio wave in which the carrier frequency of the television radio wave itself fluctuates, synchronous detection is performed by switching from the keyed type to the continuous type. The difference between the true video intermediate frequency carrier required for the above and the video intermediate frequency carrier updated only during the sample and hold period is kept to a minimum, and the inconvenience that large amplitude noise appears in the detection output due to the mismatch of the detection axes is eliminated. Therefore, it is possible to prevent the deterioration of the reproduced image quality without imposing a burden on the user.

Further, according to the present invention, the operation mode set for each selected channel is stored in advance, and the operation mode corresponding to the selected channel is read out in association with the channel selection operation to perform the keyed type or continuous type operation. Since the configuration allows the operation mode to be preset for each selected channel by designating it, the user needs to specify the operation mode for each selected channel only once at the beginning. Once you have completed
No troublesome work such as designating an operation mode for each channel selection operation is required. Therefore, for example, even in the case where the programs of two stations having different operation modes are continuously recorded by answering machine, the operation mode switching operation accompanying the channel switching is performed. It has excellent effects such as being able to leave without worrying about.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram showing an embodiment of a PLL synchronous detection type video detection device of the present invention, and FIG. 2 is a PLL of the present invention.
FIG. 3 is a circuit configuration diagram showing another embodiment of a synchronous detection type video detection device, FIG. 3 is a circuit configuration diagram showing an example of a conventional PLL synchronous detection type video detection device, and FIG. 4 is a detection phase by a quadrature ghost wave. FIG. 7 is a signal waveform diagram for explaining the deviation of the signal. 4 ... Synchronous detection circuit, 7 ... IF carrier generation circuit, 8 ... APC detection circuit, 9 ... Voltage controlled oscillator, 10 ... + 45 ° phase shift circuit, 11 ... Sample hold circuit, 12 ... Low-pass filter circuit, 15 ... Key pulse generation Circuit, 16… Open / close switch, 21,31… PLL synchronous detection system video detector, 22… Monitor circuit, 23… Peak hold circuit, 24…
Comparison circuit, 32 ... Tuning microcomputer circuit, 33 ... Data memory circuit.

Claims (2)

[Scope of utility model registration request] 1. A PLL synchronous detection type video detection device for performing synchronous detection using a video intermediate frequency carrier extracted from a video intermediate frequency signal by a phase locked loop, wherein the phase locked loop is activated only during a synchronization signal period. An operation mode switching means for switching between two types of a keyed type and a continuous type which is always activated, and a signal level of the video detection output is monitored, and when the signal level exceeds a preset constant reference, the operation mode switching circuit. On the other hand, a PLL synchronous detection system video detection device equipped with a monitoring circuit that orders switching from a keyed type to a continuous type. 2. A PLL synchronous detection type video detection device for performing synchronous detection using a video intermediate frequency carrier extracted from a video intermediate frequency signal by a phase locked loop, wherein the phase locked loop is activated only during a synchronization signal period. Type or continuous type for always activating, and an operation mode switching means for switching between two modes and an operation mode preset for each channel selected, and an operation corresponding to the channel selected in response to a channel selection operation. A PLL synchronous detection type image detection apparatus comprising an operation mode presetting means for reading out a mode and designating a keyed type or a continuous type operation for the operation mode switching circuit.