JP2865820B2 - Synchronous detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a synchronous detection device, and can be applied to, for example, a television receiver.

2. Description of the Related Art A synchronous detection apparatus of this type includes a sequential method of performing synchronous detection using a detection signal sequentially synchronized with a carrier in a received signal, and a detection method of synchronizing with the carrier every predetermined short section. There is a so-called keyed system in which synchronous detection is performed using a signal for use.

The sequential system has a simple circuit, but has a drawback that the detection operation becomes unstable due to the fluctuation of the level of the received signal or the superposition of noise or ghost.

On the other hand, in the keyed system, this disadvantage can be improved to some extent, but good detection characteristics cannot be obtained if the carrier frequency of the received signal is unstable.

Therefore, in the related art, a television receiver is provided with both a sequential system and a keyed system, and the user manually switches between them in accordance with the reception state of the television receiver.

[Problems to be Solved by the Invention] By the way, in practice, whether the sequential method or the keyed method is good may differ depending on the channel. This is because the transmission system from the broadcasting station to the television receiver is different, and the degree of mixed noise and superimposed ghost differs depending on the channel.

Therefore, if the user selects one of the methods,
A good choice for one channel may be inappropriate for another. To avoid this, every time the channel is changed, it is necessary to switch the synchronous detection method between the keyed method and the sequential method, which imposes a heavy burden on the user.

The present invention has been made in view of the above points,
It is an object of the present invention to provide a synchronous detection device that can obtain an optimal synchronous detection operation for each channel simply by selecting a channel when performing a synchronous detection operation.

[Means for Solving the Problems] In order to solve such problems, the present invention provides a synchronous detection means for synchronously detecting a video intermediate frequency signal by a detection signal, and a video intermediate frequency signal for each predetermined short section. Detection signal generating means for generating a first detection signal synchronized with the carrier of the second detection signal and a second detection signal sequentially synchronized with the carrier of the video intermediate frequency signal, and a detection selection signal preset for each channel Tuning control means for reading and outputting a detection selection signal of a tuning channel in conjunction with a tuning operation, and the first and second detection signals are supplied in parallel, and Switch control means for selecting one of the detection signals according to the detection selection signal read by the control means and inputting the selected signal to the synchronous detection means.

The present invention also provides a synchronous detection means for synchronously detecting a video intermediate frequency signal by a detection signal, a first detection signal synchronized with a carrier of the video intermediate frequency signal for each predetermined short interval, and a video intermediate frequency signal. And a detection signal generating means for selectively generating a second detection signal sequentially synchronized with the carrier wave of the detection signal in response to an external detection selection signal, and a detection selection signal preset for each channel. A tuning control means for reading a detection selection signal of a tuning channel in conjunction with a tuning operation, and switching a detection signal generated by the detection signal generating means in accordance with the read detection selection signal. It is characterized by having.

[Operation] In the present invention having such means, the synchronous detection means synchronously detects the video intermediate frequency signal by the detection signal, and the detection signal generation means converts the video intermediate frequency signal into a carrier of the video intermediate frequency signal every predetermined short section. The synchronized first detection signal and the second detection signal sequentially synchronized with the carrier of the video intermediate frequency signal are
Occurs in parallel or selectively. On the other hand, the tuning control means stores a detection selection signal set for each channel in advance, and reads and outputs a detection selection signal for each channel in conjunction with a tuning operation. As a result, the first or second detection signal according to the detection selection signal output from the tuning control means is supplied to the synchronous detection means, and an optimum synchronous detection state is always obtained by simply selecting a channel.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing one embodiment of a synchronous detection apparatus according to the present invention.

The tuner circuit 1 has a conventionally known circuit configuration for electronically switching a tuning frequency in accordance with a band switching voltage and a tuning voltage from a tuning control circuit 23 to be described later to perform tuning and frequency conversion. It is connected to the.

The video intermediate frequency amplifying circuit 3 has a conventionally known circuit configuration for amplifying and outputting the video intermediate frequency signal from the tuner circuit 1, and is connected to the synchronous detection circuit 5, the phase control circuit 11, and the carrier wave shaping circuit 15. I have.

The synchronous detection circuit 5 is a synchronous detection means, and has a conventionally known circuit configuration for switching an input video intermediate frequency signal by a detection signal synchronized with a carrier of the video intermediate frequency signal and outputting a modulated wave. Connected to the use signal generating means 17.

The detection signal generating means 17 generates a first detection signal synchronized with the carrier of the video intermediate frequency signal and a second detection signal sequentially synchronized with the carrier of the video intermediate frequency signal at predetermined short intervals. A synchronizing signal generation circuit 7, a keying pulse generation circuit 9, a phase control circuit 11, and a VCO (voltage controlled oscillator) circuit 13 for generating a first detection signal; It comprises a carrier shaping circuit 15 for generating a signal.

The synchronization signal generation circuit 7 is a circuit for oscillating and outputting a synchronization signal controlled by the frequency of the horizontal synchronization signal in the composite video signal, and is connected to the keying pulse generation circuit 9.

Although not shown, the synchronization signal generation circuit 7 detects, for example, a horizontal synchronization detection circuit that detects a horizontal synchronization signal in a composite video signal and a frequency difference between the horizontal synchronization signal and an oscillation signal from a VCO circuit described later. AFC (Automatic Frequency Control: Automatic Freq) that outputs a level signal to approach a certain level
uency Control) circuit, a loop filter circuit that suppresses high-frequency components of the level signal and converts the signal into a direct current, a VCO circuit that oscillates and outputs a signal in accordance with the frequency of the horizontal synchronizing signal in accordance with the converted level signal, It can be constituted by a synchronization pulse generation circuit that outputs a synchronization signal synchronized with the oscillation signal.

The keying pulse generation circuit 9 includes a synchronization signal generation circuit 7
A keying pulse signal is output by setting the pulse width and output timing of the synchronization signal from the controller, and is connected to the phase control circuit 11.

The phase control circuit 11 forms an error signal that brings the phase difference between the carrier of the video intermediate frequency signal and a first detection signal from the VCO circuit 13 described later close to a predetermined level, and also generates the error signal by each keying pulse. It is a circuit that samples and holds at the timing of the signal, and outputs a DC level control signal that further suppresses the high frequency components of the sample and hold signal, and is connected to the VCO circuit 13.

The VCO circuit 13 is a circuit that oscillates and outputs a first detection signal whose phase changes according to a control signal from the phase control circuit 11, and is connected to the switch circuit 19.

The carrier wave shaping circuit 15 is a circuit that amplifies the carrier of the video intermediate frequency signal and limits the amplitude thereof to a constant value, thereby outputting a second detection signal sequentially synchronized with the carrier. It is connected.

The switch circuit 19 is a switch control means for inputting the first or second detection signal to the synchronous detection means in accordance with a detection selection signal from a channel selection control circuit 23 described later.

The tuning control means 27 is a means for storing a detection selection signal set in advance for each channel, reading and outputting a detection selection signal for each channel in conjunction with a tuning operation, and includes a channel button circuit 21, It comprises a tuning control circuit 23, a control data setting circuit around it, and a memory circuit 25.

The channel button circuit 21 is, for example, a conventionally known circuit having tuning buttons for 12 channels (including UHF), and is connected to the tuning control circuit 23.

The tuning control circuit 23 is a circuit that performs the selection control of the synchronous detection method according to the present invention and the tuning control of, for example, a conventionally known so-called voltage synthesizer method. A memory controller for controlling the circuit 25, an A / D converter for converting an analog signal such as a tuning voltage generated by the potentiometer VR into a digital signal, and a digital signal such as a tuning voltage read from the memory circuit 25 for analog. A D / A converter for converting into a signal is included. The tuning control circuit 23 includes, in addition to the peripheral control data setting circuit, the memory circuit 25 and the tuner circuit 1.
And a switch circuit 19 are connected.

The memory circuit 25 is a circuit for storing a detection selection signal, a band switching signal, and a tuning voltage signal set for each channel, and FIG. 2 shows a data storage structure of the embodiment.

In FIG. 2, a memory circuit 25 stores control data consisting of 15 bits at each address corresponding to a channel number. In the "keyed" column of the control data, a 1-bit detection selection signal is stored. When "keyed" = 1, the tuning control circuit 23 causes the switch circuit 19 to select the first detection signal, and the "keyed" When = 0, the second detection signal is selected. In the “band” column, a 2-bit band switching signal is stored. When “band” = 1, the tuning control circuit 23 outputs a VL band band switching voltage to the tuner circuit 1, and “band” = 2 In the case of, the band switching voltage of the VH band is output, and when "band" = 3, the band switching voltage of the U band is output. In the “tuning voltage” column, a 12-bit tuning voltage signal is stored. For example, “tuning voltage” = 1800
In this case, the tuning control circuit 23 applies a tuning voltage of 18 volts to the tuner circuit 1; when "tuning voltage" = 1200, a tuning voltage of 12 volts is added; when "tuning voltage" = 600, 6 volts is applied. Apply tuning voltage.

Next, the operation of the present invention thus configured will be described. The tuner circuit 1 electronically switches the tuning frequency according to the band switching voltage and the tuning voltage from the tuning control circuit 23, and performs tuning and frequency conversion.

The video intermediate frequency signal frequency-converted by the tuner circuit 1 is amplified by the video intermediate frequency amplification circuit 3 and
Is added to

The synchronous detection circuit 5 performs synchronous detection of the video intermediate frequency signal using the first or second detection signal selected by the switch circuit 19.

In order to generate the first detection signal, the synchronizing signal generating circuit 7 oscillates and outputs a synchronizing signal controlled by the frequency of the horizontal synchronizing signal in the composite video signal, and the keying pulse generating circuit 9 generates the synchronizing signal. A keying pulse signal in which the pulse width and output timing of the signal are set is output.
An error signal is formed so as to bring the phase difference of the first detection signal from the VCO circuit 13 close to a predetermined level, the error signal is sampled and held at the timing of each keying pulse signal, and the high level of the sample and hold signal is obtained. Outputs a DC level control signal with suppressed frequency components, and
The circuit 13 oscillates and outputs a first detection signal whose phase changes according to the control signal.

The carrier shaping circuit 15 amplifies the carrier of the video intermediate frequency signal and limits the amplitude of the carrier to output a second detection signal sequentially synchronized with the carrier.

Then, the switch circuit 19 inputs the first or second detection signal to the synchronous detection circuit 5 according to the detection selection signal from the channel selection control circuit 23.

Under the above conditions, if the user wants to store the control data for each channel, the switch S1 of the control data setting circuit is first set to the "set" side. This makes + B
The voltage is applied to the control data setting circuit, and the tuning control circuit 23
Enters the setting mode. Next, when the user presses a desired channel button, a band switching voltage and a tuning voltage corresponding to the channel button and the set values of the band switch S3 and the potentiometer VR at that time are output to the tuner circuit 1. Further, it causes the switch circuit 19 to output a detection selection signal according to the setting of the switch S4. Then, a corresponding image is obtained on a screen (not shown).

In this state, if the band selection is deemed inappropriate, the user switches the band switch S3 to the VL, VH or U band corresponding to the channel. To obtain a clearer image, the user adjusts the tuning voltage with the potentiometer VR. Furthermore, when a user wants to obtain better detection characteristics, the user can switch the upper keyed (K) with the switch S4.
Switch to system or lower sequential system.

When a desired image receiving characteristic is obtained on the screen, the user presses the memory switch S2 and inputs the strobe signal ST to the channel selection control circuit 23. As a result, the tuning control circuit 23 forms control data including “keyed”, “band”, and “tuning voltage” and stores the control data in the memory circuit 25 at the address of the channel number.

Thus, the user performs the above setting operation in advance for all useful channels, and when the setting is completed, the switch S1
To the "image receiving" side. As a result, the tuning control circuit 23 enters the image receiving mode.

Thereafter, when the user presses a desired channel button, the tuning control circuit 23 reads out control data from the corresponding address of the memory circuit 25 and outputs a signal to the tuner circuit 1 and the switch circuit 19 in response to this. That is, the "band" and "tuning voltage" in the control data are D / A converted to the corresponding band switching voltage and tuning voltage and added to the tuner circuit 1. For "keyed", if "keyed" =
When "1", a detection selection signal for selecting the first detection signal is output to the switch circuit 19. When "keyed" = 0, a detection selection signal for selecting the second detection signal. Is output to the switch circuit 19.

As described above, in the synchronous detection device of the present invention, the detection selection signal set in advance for each channel is stored, and the detection selection signal for each channel is read out in conjunction with the channel selection operation. Switches the synchronous detection operation of the system.

Therefore, even if the receiver is installed in any environment, a better synchronous detection operation can be set for each channel in advance, and a better synchronous detection operation can be obtained for each channel simply by selecting a channel at the time of reception.

In the above embodiment, the detection signal generating means 17 for generating the first and second detection signals is employed, but the present invention is not limited to this. The reason is that if the phase control circuit 11 is not controlled by the keying pulse signal, the VCO circuit 13 can easily be operated as a circuit for generating a sequential second detection signal. Therefore, for example, if the carrier wave shaping circuit 15 and the switch circuit 19 are omitted, and instead the detection selection signal is input to the phase control circuit 11 as a signal for energizing or deactivating the keying pulse signal, the first or This is because the detection signal generation means 17 for generating the second detection signal can be obtained.

Further, in the above-described embodiment, a voltage synthesizer type is described as the channel selection control means 27. However, the present invention can be similarly applied to other potentiometer preset types and frequency synthesizer types.

[Effects of the Invention] As described above, according to the present invention, the first detection signal synchronized with the carrier of the video intermediate frequency signal and the carrier of the video intermediate frequency signal are sequentially synchronized in predetermined short intervals. Tuning control means for generating a second detection signal and storing a detection selection signal set for each channel in advance reads and reads the detection selection signal of the selected channel in conjunction with the tuning operation. The switch control means to which the first and second detection signals are supplied in parallel according to the detected detection selection signal is switched, and one of the detection signals is selected and input to the synchronous detection means. A detection selection signal set for each channel is stored, and a detection selection signal for each channel is read out in conjunction with a channel selection operation to switch between keyed and sequential synchronous detection operations. As long as settings are made in accordance with the installation environment of the receiver, an excellent effect is obtained such that a good image can always be obtained for the channel by simply selecting a channel during the reception operation.

Also, in the present invention, the detection signal generating means may sequentially synchronize the first detection signal synchronized with the carrier of the video intermediate frequency signal and the carrier of the video intermediate frequency signal every predetermined short section. A detection signal is selectively generated in accordance with an external detection selection signal, and a channel selection control unit that stores a detection selection signal set for each channel in advance is tuned in conjunction with a channel selection operation. Read the channel detection selection signal,
Since the detection signal generation means is configured to switch the detection signal generated according to the read detection selection signal,
An apparatus which can switch the tuning control means between a keyed system and a sequential system according to a detection selection signal, thereby simplifying the configuration of the detection signal generating means and simultaneously executing the keyed system and the sequential system. This eliminates the need for a switch control means between the synchronous detection circuit and the detection signal generation means required by the method described above, and has the effect of simplifying the entire circuit configuration.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a synchronous detection device according to the present invention, and FIG. 2 is a diagram showing a data storage structure of the embodiment in the memory circuit shown in FIG. DESCRIPTION OF SYMBOLS 1 ... Tuner circuit 3 ... Video intermediate frequency amplifier circuit 5 ... Synchronous detection means (synchronous detection circuit) 7 ... Synchronous signal generation circuit 9 ... Keying pulse generation circuit 11 ... Phase control circuit 13 ... VCO circuit 15 ... Carrier wave shaping circuit 17 ... Detection signal generating means 19 ... Switch control means (switch circuit) 21 ... Channel button circuit 23 ... Tuning control circuit 25 ... Memory circuit 27 ... Tuning control means

Claims (2)

(57) [Claims] A synchronous detection means for synchronously detecting a video intermediate frequency signal by a detection signal, and a first detection signal and a video intermediate frequency signal synchronized with a carrier of the video intermediate frequency signal for each predetermined short section. A detection signal generating means for generating a second detection signal sequentially synchronized with a carrier wave, and a detection selection signal set in advance for each channel are stored, and the detection selection signal for the selected channel is linked with the tuning operation. Channel selection control means for reading and outputting a signal; and the first and second detection signals are supplied in parallel, and one of the detection signals is selected according to the detection selection signal read by the channel selection control means. And a switch control means for inputting the signal to the synchronous detection means. 2. A synchronous detection means for synchronously detecting a video intermediate frequency signal by a detection signal, and a first detection signal synchronized with a carrier of the video intermediate frequency signal and a video intermediate frequency signal at predetermined short intervals. A second detection signal sequentially synchronized with the carrier, a detection signal generating means for selectively generating the second detection signal in response to an external detection selection signal, and a detection selection signal previously set for each channel, and A tuning control means for reading a detection selection signal of a tuning channel in conjunction with a tuning operation, and switching a detection signal generated by the detection signal generation means in accordance with the read detection selection signal. A synchronous detector characterized by the above-mentioned.