JPH06205318A - Automatic phase control circuit - Google Patents

Abstract

PURPOSE:To reduce the switching time for a PLL response range by quickening an operating timing of lock detection. CONSTITUTION:A VMUTE (video mute) signal outputted from a microcomputer at channel tuning or non-signal at a weak electric field whose output timing is faster than that of a lock detection signal is employed. When the VMUTE signal is outputted, a transistor(TR) 26 is turned on to add a resistor 22 to an automatic phase control filter 30 comprising a capacitor 8 and resistors 20, 21 thereby changing a time constant of the same filter 30 and widening a PLL frequency reply range. Since the output timing of the VMUTE signal is set faster than that of the lock detection signal, it is possible to vary the reply range of a phase detection circuit 3 in a faster timing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic phase control circuit suitable for use in a PLL synchronous detection circuit of a split carrier type television receiver.

[0002]

2. Description of the Related Art Conventionally, split carrier type television receivers have been developed. The split carrier method is a method in which a video signal and an audio signal are separated and processed in an IF circuit, and since the video signal component is not mixed in the audio signal, it has an advantage that no audio interference such as buzz or buzz beat occurs. is doing.

FIG. 3 is a block diagram when a conventional automatic phase control circuit is applied to a PLL synchronous detection circuit of a split carrier type television receiver. In this figure,
A broadband SAW (Surface Acoustic Wave) filter 1 is supplied with an intermediate frequency signal of video and audio output from a tuner (not shown). This broadband S
The AW filter 1 has an amplification characteristic for stably amplifying a received channel signal and suppressing other unnecessary signals. An intermediate frequency amplifier circuit 2 amplifies the intermediate frequency signal output from the wide band SAW filter 1. The output of the intermediate frequency amplification circuit 2 is supplied to the phase detection circuit 3 and the video detection circuit 4.

The phase detection circuit 3 includes an intermediate frequency signal and a voltage controlled oscillator circuit (VCO: Voltage C-ontrolled Oscillat).
or) detects a phase difference from the signal oscillated in 5 and generates a signal corresponding to the phase difference, and supplies this signal to the VCO 5 through an automatic phase control filter 9 composed of resistors 6, 7 and a capacitor 8. . Since the VCO 5 is controlled by this signal, it oscillates with the same degree of stability as the intermediate frequency signal. Reference numeral 5A is a tuning frequency oscillator used for the VCO 5, and is composed of a capacitor and a coil as shown.

Reference numeral 10 denotes a (+) 45 ° phase circuit, which has a VC
The output of O5 is advanced by 45 ° and output. 11 is (-)
It is a 45 ° phase circuit, which delays the output of the VCO 5 by 45 ° and outputs it. The video detection circuit 4 receives the reference carrier signal output from the VCO 5 via the (-) 45 ° phase circuit 11 and detects the intermediate frequency signal by this signal. 1
3 is a 4.5 MHz trap, which removes the audio intermediate frequency signal and outputs a video signal.

Reference numeral 14 is a lock detection circuit, which is composed of a lock detector 15 and a transistor 16. The lock detector 15 detects a PLL lock state and outputs a lock detection signal. When the lock detection signal is not output from the lock detection circuit 14, the transistor 16 is off, and the automatic phase control filter 9 includes the capacitor 8, the resistor 6, and the resistor 6.
7, the response range of the phase detection circuit 3 is wide. On the other hand, when the lock detection signal is output, the transistor 16 is turned on, the automatic phase control filter 9 is composed of the capacitor 8 and the resistor 6, and the response range of the phase detection circuit 3 is narrowed.

In the figure, reference numeral 17 is a resistor through which a power supply Vcc is supplied from the outside. The phase detection circuit 3, the VCO 5, the oscillator 5A, the resistors 6 and 7, the capacitor 8, the (+) 45 ° phase circuit 10, the (−) 45 ° phase circuit 11 and the lock detection circuit 14 are the automatic phase control circuit 5.
Configure 0.

In such a configuration, the broadband SAW filter 1 removes unnecessary components from the intermediate frequency signal output from the tuner (not shown). Then, after being amplified by the intermediate frequency amplification circuit 2, it is supplied to the video detection circuit 4 and the phase detection circuit 3. The phase detection circuit 3 detects the phase difference between the intermediate frequency signal and the signal oscillated by the VCO 5,
A signal corresponding to the phase difference is output.

Then, this signal is supplied to the VCO 5 through the automatic phase control filter 9, and the VCO 5 is controlled by this signal and oscillates with the same degree of stability as the intermediate frequency signal. Then, simultaneous detection is performed by the VCO signal controlled so as to match the phase of this intermediate frequency signal, and the resulting video signal is output via the 4.5 MHz trap 13 and supplied to the lock detection circuit 14. To be done.

When the lock detection circuit 14 detects the PLL lock state, a lock detection signal is output, the transistor 16 is turned on, and the automatic phase control filter 9 is composed of the capacitor 8 and the resistor 6, whereby phase detection is performed. The response range of the circuit 3 becomes narrow. Then, when the lock detection circuit 14 stops outputting the lock detection signal from this state to the channel switching (channel tuning) state or the non-signal state in the weak electric field, the transistor 16
Is turned off, and the low-pass filter 9 is composed of a capacitor 8 and resistors 6 and 7. This widens the response range of the phase detection circuit 3 and enables early synchronization.

[0011]

By the way, in the above-mentioned conventional automatic phase control circuit, since the timing of the lock detection operation is late, it takes a long time to switch the response range of the phase detection circuit. There has been a problem that it takes a long time to start image detection after the normal state is restored from a no-signal state in a weak electric field.

Therefore, an object of the present invention is to provide an automatic phase control circuit that can shorten the lock detection time.

[0013]

To achieve the above object, an automatic phase control circuit according to the present invention comprises a voltage controlled oscillator circuit,
A phase detection circuit that detects a phase difference between an input signal and a signal oscillated by the voltage controlled oscillation circuit, and a low-pass filter that uses the phase difference detected by the phase detection circuit as an input voltage of the voltage controlled oscillation circuit. A filter, a lock detection circuit that detects a phase lock state of the input signal and a signal oscillated by the voltage controlled oscillation circuit, and outputs a lock detection signal, and a lock detection circuit that detects the response range of the phase detection circuit. And an automatic phase control filter that varies based on a lock detection signal output from the circuit or a control signal input from the outside.

[0014]

In the present invention, the response range of the phase detection circuit is changed by the control signal supplied from the outside in addition to the lock detection signal. As the control signal, specifically, the VMUTE output from the control unit (microcomputer) when the channel is switched is used.
A (video mute) signal is preferred. This VMUT
Since the E signal is output during channel tuning or when there is no signal in a weak electric field, switching of the response range of the phase detection circuit becomes faster than when the lock detection signal is used.

Therefore, the switching of the response range of the phase detection circuit becomes faster, and the lock detection time becomes shorter.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a PL of a split carrier type television receiver to which an automatic phase control circuit according to the present invention is applied.
It is a block diagram which shows an L synchronous detection circuit. In this figure, the same parts as those in FIG. 3 described above are designated by the same reference numerals and the description thereof will be omitted.

As shown in FIG. 1, the automatic phase control filter 30 comprises a capacitor 8 and resistors 20-22. The lock detection circuit 14A detects the lock state of the PLL together with the lock detection filter (capacitor) 23, and outputs the lock detection signal when the lock state is detected. In this case, the output is set to "H" level.

Between the output terminal of the lock detection circuit 14A and the input terminal _Tc for inputting the control signal, diodes 24 and 25 are connected in series with their polarities reversed. The base of the transistor 26 is connected to the common connection portion of the diodes 24 and 25. The collector of the transistor 26 is connected to one end of the resistor 22, and the emitter is grounded.

The structure of the automatic phase control filter 30 changes depending on whether the transistor 26 is turned on or off. That is, when the transistor 26 is turned off, one end of the resistor 22 is opened and the capacitor 8 and the resistors 20 and 21 are formed. On the other hand, when the transistor 26 is turned on, one end of the resistor 22 is grounded by the transistor 26, and the resistor 22
Is added, the response range of the phase detection circuit 3 is widened.

On the other hand, the control signal supplied to the input terminal T _c is V output from the control unit (microcomputer) provided in the television receiver.
The MUTE signal is preferred. This VMUTE signal is output when the channel is switched or when there is no signal in a weak electric field, and is output earlier in timing than the lock detection signal output from the lock detection circuit 14A.

Here, FIG. 2 shows a lock detection signal, VMUT.
It is a timing chart of the E signal and the like, and it can be seen that the VMUTE signal is output earlier in timing than the lock detection signal as shown in this figure. Hereinafter, this figure will be described in detail for reference.

When the channel 2 button is pressed while receiving channel 1, the audio signal is muted first. Next, at time t ₁ , the VMUTE signal changes from “L” to “H”. Then, at time t ₂ , the locked state is released and the channel setting by the microcomputer is started.

[0023] from the time the lock state is released gradually been an increase in the TV voltage, and at the time t ₃ lock detection signal is changed from "L" to "H". This causes the channel change. Then, after entering the PLL lock state at time t ₄ , the lock detection signal changes from “H” to “L” at time t ₅ . Then, after the time t ₅ , various processes are performed, the VMUTE signal changes from “H” to “L” at the time t ₆ , and the reception of the channel 2 is started.

Returning to FIG. 1, the phase detection circuit 3, the VCO 5,
Oscillator 5A, capacitor 8, (+) 45 ° phase circuit 1
0, (-) 45 ° phase circuit 11, lock detection circuit 14A
And the resistors 20 to 22 form an automatic phase control circuit 60.

In such a structure, for example, when the VMUTE signal is not supplied to the diode 24 and the lock detection signal is not supplied to the diode 25 while the broadcast of the channel 1 is being received, the transistor 2 is supplied.
Since 6 is in the off state, the automatic phase control filter 30 is composed of the capacitor 8 and the resistors 20 and 21, and the response range is narrowed.

In this state, for example, when channel tuning is performed, the VMUTE
A signal is output and supplied to the diode 24. As a result, the transistor 26 is turned on, the automatic phase control filter 30 is composed of the capacitor 8 and the resistors 20, 21, and 22 (that is, the resistor 22 is added), and the phase detection circuit 3
The response range of switches. In this case, the response range is wide. As shown in FIG. 2, after the VMUTE signal is output at time t ₁ , the lock detection signal is output at time t ₂ and is supplied to the diode 25.

As described above, by using the VNUTE signal, switching of the response range of the phase detection circuit 3 becomes faster, and the lock detection time becomes shorter.

By applying this embodiment to a television receiver mounted on a vehicle such as an automobile whose electric field constantly changes, a stable reception state can be obtained.

[0029]

According to the present invention, in addition to the lock detection signal, a control signal (VMUTE signal in the embodiment) output at a timing faster than the lock detection signal is used to vary the response range of the phase detection circuit. By doing so, the switching of the response range of the phase detection circuit becomes faster, and the lock detection time becomes shorter. As a result, the time from the time of channel tuning or when there is no signal such as a weak electric field to the start of video detection is shortened.

[Brief description of drawings]

FIG. 1 is a block diagram showing a PLL synchronous detection circuit of a split carrier type television receiver to which an automatic phase control circuit according to the present invention is applied.

FIG. 2 is a time chart of various signals in the embodiment.

FIG. 3 is a block diagram showing a PLL synchronous detection circuit of a split carrier type television receiver to which a conventional automatic phase control circuit is applied.

[Explanation of symbols]

 3 Phase Detection Circuit 5 VCO (Voltage Controlled Oscillation Circuit) 8,23 Capacitor 10 (+) 45 ° Phaser 11 (-) 45 ° Phaser 14A Lock Detection Circuit 20, 21, 22 Resistor 24, 25 Diode 26 Transistor 30 Automatic Phase control filter

Claims (1)

[Claims] 1. A voltage control oscillation circuit, a phase detection circuit for detecting a phase difference between an input signal and a signal oscillated by the voltage control oscillation circuit, and a phase difference detected by the phase detection circuit for the voltage. A low-pass filter that is an input voltage of the control oscillation circuit, a lock detection circuit that detects a lock state of a phase between the input signal and a signal oscillated by the voltage control oscillation circuit, and outputs a lock detection signal, An automatic phase control circuit, comprising: an automatic phase control filter that changes a response range of the phase detection circuit based on a lock detection signal output from the lock detection circuit or a control signal input from the outside. .