JPH04132316A - Low-pass filer changeover circuit - Google Patents

Abstract

PURPOSE:To prevent disturbance of synchronization when the user receives a radio wave including a residual phase modulation component by a television receiver by providing an optional low-pass filter changeover circuit to the system. CONSTITUTION:An optional low-pass filter circuit is provided to the system. That is, a transistor(TR) 10 connecting to a power supply through a switch 13 is operated, a diode 7 stops its operation and a resistor 5 is connected in series with a low pass filter 18. Thus, a lock/nonlock detection circuit 17 is locked and its output is short-circuited, then a time constant of the low-pass filter 18 is reduced optionally by connecting the switch 13 to the power supply. Thus, when a strong radio wave including a residual phase modulation component is received, the time constant is decreased by connecting the switch 13 to the power supply thereby quickening the tracking to an incoming radio wave and preventing disturbance of synchronization.

Description

[Detailed Description of the Invention] Industrial Field of Application The present invention is applicable to high-frequency video signals received by television receivers, etc. that contain a residual position modulation component (the phase of the carrier wave changes with the amplitude of the video signal). In order to detect synchronization disturbances that tend to occur in some cases and minimize synchronization disturbances in television receivers, the low-pass filter used in the phase control circuit that controls the oscillation frequency of the voltage-controlled oscillator for intermediate frequency detection can be optionally used. The present invention relates to a low-pass filter switching circuit configured to switch.

BACKGROUND ART In conventional television receivers, in a circuit that has its own oscillator as a detection means for an intermediate frequency detection circuit, switching of a low-pass filter for phase locking is performed by a video signal lock/unlock detection circuit. This is done by switching the frequency pull-in range depending on the strength.

The conventional configuration will be described below with reference to the drawings.

FIG. 6 shows the configuration of a conventional intermediate frequency detection circuit, in which the intermediate frequency amplification section 51° intermediate frequency detection circuit 6
2. Voltage controlled oscillator 63° phase controlled detection circuit 54. Lock time constant switching unit (hereinafter referred to as low-pass filter) 55.
It is composed of a lock/unlock detection circuit 56. The operation of the circuit configured as above will be described below.

The intermediate frequency video signal is amplified by an intermediate frequency amplification section 51 and then sent to an intermediate frequency detection circuit 52 and a phase control detection circuit 54. The phase control detection circuit 54 uses the frequency input from the voltage control oscillator 63 to generate an intermediate frequency amplification section 61.
After phase-detecting the intermediate frequency video signal input from
This signal passes through a low-pass filter 66 and controls the phase of the voltage controlled oscillator 530. The low-pass filter 65 is controlled by a lock/unlock detection circuit 56 depending on the strength of the received radio waves. When the received radio waves are strong, the output of the lock/unlock detection circuit 56 is grounded and the time constant of the low-pass filter 55 becomes heavy. Therefore, the frequency pull-in range becomes narrower. Conversely, when the received radio waves are weak, the output of the lock/unlock detection circuit 66 is open, and the time constant of the low-pass filter is light, so the frequency pull-in range becomes wide. Conventionally, a so-called complete synchronous detection circuit having the above circuit configuration has been used.

Problems to be Solved by the Invention As mentioned above, the time constant of the low-pass filter used in conventional circuits detects only the strength and weakness of the received radio waves to the television receiver and switches, and the residual phase to the television receiver is When receiving strong radio waves containing modulated components, the time constant of the low-pass filter is heavy, making it slow to follow the incoming radio waves, causing distortion in the synchronization signal part of the detected video signal and causing synchronization disturbance. was.

In recent years, with the spread of video tape recorders and game devices, the number of devices that generate radio waves (high frequency signals) containing residual phase modulation components has increased, and when these devices are connected to a television receiver, synchronization disturbances and synchronization errors may occur. This often caused discomfort to the users and even made it impossible to use these devices.

Means for Solving the Problems In order to solve the above problems, the present invention provides a new arbitrary low-pass filter switching circuit to prevent synchronization disturbance when a user receives radio waves containing residual phase modulation components with a television receiver. It was designed to prevent this.

Function The present invention provides an arbitrary low-pass filter switching circuit as described above, and when a synchronization disturbance occurs in a television receiver, the time constant of the low-pass filter is lightened to speed up the response and eliminate the synchronization disturbance. It is designed to eliminate discomfort for the receiver user.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to the drawings. FIG. 1 shows the circuit configuration of an arbitrary low-pass filter switching circuit in one embodiment of the present invention.

In addition to the conventionally used O-pass filters 1, 2, 3.4 in FIG. 1 (described in FIG. 5), a low-pass filter resistor 5. DC blocking capacitor 6.8. DC resistor 9 for making diode 7 conductive. A switching transistor 10°, a current control resistor 11, 12, and a switching 13 are newly provided. The operation of the circuit configured as above will be explained below.

The intermediate frequency video signal is amplified by the intermediate frequency amplification section 14 and then sent to the phase control detection circuit 16. The phase control detection circuit 16 phase-detects the intermediate frequency input from the intermediate frequency amplification section 14 using the oscillation frequency input from the voltage control oscillator 16, and outputs the output to a low-pass filter 18.
is sent to the voltage controlled oscillator 16 through. In normal operation, the switch 13 is connected to the ground side, the transistor 10 stops operating, and current flows from the diode 7 to the resistor 9, causing the resistor 5 to be in an alternating current short-circuited state. It operates in the same way as a low-pass filter.

Next, when the switch 13 is connected to the power supply side, the transistor 1o becomes active, the diode 7 stops operating, and the resistor 5 is placed in series with the low-pass filter. In other words, even if the lock/unlock detection circuit 17 is in the locked state and its output is short-circuited, the time constant of the low-pass filter can be arbitrarily lightened (the equated bandwidth can be reduced by connecting the switch 13 to the power supply). change) is possible. Therefore, by connecting the switch 13 to the power supply side when a strong radio wave containing a residual phase modulation component is received, it is possible to reduce the time constant, speed up tracking of the incoming radio wave, and prevent synchronization disturbance. .

In this embodiment, the time constant of the low-pass filter 18 is switched by the switch 13, but in order to detect synchronization disturbance, a synchronization detection circuit 3o using horizontal pulses and synchronization signals from the horizontal deflection circuit is used as shown in FIG. It is also possible to automatically detect synchronization disturbances using a synchronous circuit and connect its output to the resistor 12 shown in FIG.

In addition, in order to switch the time constant of the low-pass filter, the user stores switch data in advance in the memory integrated circuit (for example, memory IC) 33 by the user control switch 31 for each television channel as shown in FIG. It may also be automatically output from the microcomputer 32.

Furthermore, as shown in FIG. 4, a synchronization detection circuit 44 that uses synchronization signals and horizontal pulses to switch the low-pass filter time constant.
In addition, the output of the storage integrated circuit 43 stored by the user control switch 41 is also input to the microcomputer 42 as data input, and both outputs are output from the microcomputer 42. You may let them.

Effects of the Invention As described above, the present invention can arbitrarily increase the time constant of the low-pass filter of the phase control detection section (PLL) even when a television receiver receives strong radio waves containing residual phase modulation components. It is possible to prevent synchronization disturbance and obtain good images.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a low-pass filter switching circuit in an embodiment of the present invention, and FIGS. 2 and 3. FIG. 4 is a circuit diagram for detecting synchronization disturbance according to claims 2 and 3.4, and FIG. 6 is a circuit diagram of a conventional low-pass filter. 10... Switching transistor, 13...
... Switch, 14 ... Intermediate frequency amplification section, 16 ... Phase control detection circuit, 16 ...
・Voltage controlled oscillator, 17... Lock/unlock detection circuit, 18... Low pass filter, 30, 4
4...Synchronization detection circuit, 33°43...
Memory integrated circuit (memory IC), 32°42...
...Microcomputer. Name of agent: Patent attorney Akira Okaji and 2 others Figure 2 Darkness 111 Ran #1 Jurisdiction Exit Route Kozaf Troll Switch Mic 0F+/Gekota

Claims (4)

[Claims] (1) Means for detecting an intermediate frequency using a complete synchronous detection circuit including a voltage controlled oscillator operating at an intermediate frequency, a phase controlled detection circuit, and a lock/unlock detection circuit, and a phase controlled detection circuit that controls the voltage controlled oscillator. A low-pass filter switching circuit in which the time constant of the low-pass filter can be arbitrarily changed using a switch. (2) The low-pass filter switching circuit according to claim 1, wherein the switch circuit according to claim 1 comprises a synchronization detection circuit using a synchronization signal and a horizontal pulse. (3) The low-pass filter switching circuit according to claim 1, wherein the switch circuit according to claim 1 comprises a microcomputer output stored in a storage integrated circuit. (4) The low-pass filter switching circuit according to claim 1, wherein the switch circuit according to claim 1 comprises a synchronization detection circuit using a synchronization signal and a horizontal pulse, and a microcomputer output stored in a storage integrated circuit. .