JP3314722B2 - TV signal channel selection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a television
More specifically, the present invention relates to a local oscillator circuit of a PLL synthesizer system, and an AFT circuit for detecting an intermediate frequency carrier signal and extracting an automatic tuning (AFT) control signal. The present invention relates to a tuning device for quickly stabilizing a local oscillation frequency signal in a combined TV signal tuning device.

[0002]

2. Description of the Related Art Conventionally, as a channel selection device for a television signal in a television receiver or a VTR device, for example, Japanese Patent Publication No.
There is a technique using a local oscillator circuit of a synthesizer type using a phase locked loop (PLL) as disclosed in Japanese Patent No. 27846. Such a PLL synthesizer type local oscillation circuit and an AFT for detecting an intermediate frequency carrier signal and extracting an automatic tuning (AFT) control signal.
In the case of a TV signal tuning device combining a circuit and
The control of the circuit of the LL synthesizer system is performed by widening the frequency change range of the local oscillator circuit, for example, by changing the frequency change range from a conventional 18-bit step to a 19-bit step, and controlling the AFT circuit. If the local oscillation frequency change range is changed while maintaining the control in a very narrow frequency change range of 1 bit (for example, 27.965195 KHz), a noise screen appears at the time of channel selection.

[0003]

SUMMARY OF THE INVENTION The present invention relates to a television which combines such a local oscillator circuit of the PLL synthesizer type and an AFT circuit for detecting an intermediate frequency carrier signal and extracting an automatic tuning (AFT) control signal. It is an object of the present invention to provide a television signal tuning device which can solve the problem that it takes a long time for the circuit to be stabilized at the time of selecting a signal and a noise screen appears.

[0004]

According to a first aspect of the present invention, there is provided a television signal tuning apparatus for amplifying a reception signal received by an antenna;
A local oscillator circuit of the L synthesizer type, a mixing circuit for mixing an output signal of the local oscillator circuit and an output signal of the high frequency amplifier circuit, and an intermediate frequency carrier signal output from the mixing circuit for frequency detection and automatic tuning ( subjecting the AFT control signal to the local oscillation circuit with be <br/> eject the AFT) control signal
And AFT circuit for correcting the local oscillation frequency supply, and a signal detecting circuit for detecting the presence of the received signal, the local oscillator
Occurs when the local oscillation frequency of the circuit is at a predetermined reference frequency.
When the generated AFT control signal is stored as a reference level,
Also, when the AFT control signal appears, the reference level
In the upper region with respect to the bell, according to the AFT control signal.
The first region or the base region where the variation range of the local oscillation frequency
A lower area with respect to the reference level, wherein the AFT control signal
Any of the second regions where the local oscillation frequency change range due to
Determine whether the AFT control signal exists in the area
A control unit that controls the local oscillation frequency of the local oscillation circuit according to a channel selection operation, and in a state where a reception signal is detected by the signal detection circuit , the control unit
When the AFT control signal is in the first area.
And beyond the first area and first into the second area.
In Rutotomoni changing the local oscillation frequency of the local oscillator circuit by a change Tesuppu wide frequency variation range, the AF
When the T control signal is present in the second area, the local oscillation frequency of the local oscillation circuit is changed in a change step of a narrow frequency change range which is a fraction of the change step in the first area , and the AFT control signal is A constant value without fluctuation
At this point, the control of the local oscillation frequency is terminated.
Has been established .

According to a second aspect of the present invention, in the television signal tuning apparatus according to the first aspect, a change range of the local oscillation frequency in the first area is 8 bits, and the local oscillation frequency in the second area is 8 bits. The change range is 1 bit.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block circuit diagram showing one embodiment of a television signal tuning device of the present invention. In the figure, in a frequency synthesizer type channel selection device 1, a frequency f0 corresponding to a channel selected by a channel selection operation section 2 is supplied from a microcomputer 3 to a latch register 4. The frequency f0 of the selected channel is stored (preset) in the memory 5 provided in the microcomputer 3, and
The latch register 4 holds this frequency f0, and
Alternatively, the holding is continued until another frequency f0 is given. The output (frequency f0) of the latch register 4 is supplied to the phase detector 7 via the programmable frequency divider 6.

The frequency synthesizer type tuning apparatus 1 includes a reference oscillator 8, and a clock pulse generating circuit 9 generates a clock pulse based on the oscillation output of the reference oscillator 8 and supplies the clock pulse to the microcomputer 3. The oscillation frequency from the reference oscillator 8 is frequency-divided by a fixed frequency divider 10 at a predetermined frequency division ratio, and is provided to the phase detector 7. In the phase detector 7, a detection output is obtained based on the frequency f1 given from the variable frequency divider 6 and the frequency f2 given from the fixed frequency divider 10. That is, when the frequency f1 is equal to the frequency f2, the detection output is 0. When the frequency f1 is higher than the frequency f2, a positive detection output is obtained.
When the frequency f1 is smaller than the frequency f2, a negative detection output is obtained. The low-pass filter 11 is a phase detector 7
A tuning voltage is output to a local oscillator 13 including a voltage controlled oscillator (VCO) inside the tuner 12 based on the output from the tuner 12. The oscillation frequency of the voltage controlled oscillator 13 is controlled by the tuning voltage.

In the tuner 12, a high-frequency television signal received by an antenna (not shown) is amplified by a high-frequency amplifier circuit 14 and mixed with an oscillation frequency from a voltage-controlled oscillator 13 by a mixing circuit 15, thereby producing a video signal. An intermediate frequency signal is extracted. This video intermediate frequency signal is amplified by the video intermediate frequency amplification circuit 16 and the video signal processing circuit 17
Given to. The oscillation frequency from the voltage controlled oscillator 13 is divided by the prescaler 18 at a predetermined division ratio, and is provided to the variable frequency divider 6. The variable frequency divider 6 changes the frequency division ratio based on the frequency f3 given from the prescaler 18, and is adjusted so that the frequency f1 and the frequency f2 become equal.

The output from the video intermediate frequency amplifier 16 is
The signal is supplied to an automatic tuning (AFT) circuit 19. In the automatic tuning (AFT) circuit 19, the video intermediate frequency carrier is extracted and amplified, then the amplitude is made constant, and the frequency (FM) is detected. Then, a change in the frequency is extracted as a change in the DC voltage. After this voltage is amplified, unnecessary components are removed, and the voltage-controlled oscillator 13 of the tuner 12 outputs
It is supplied as a T voltage. The frequency of the voltage controlled oscillator 13 is corrected by the output (AFT voltage) of the AFT circuit 19, and the intermediate frequency of the video intermediate frequency carrier signal is made constant. The AFT voltage is given to the microcomputer 3,
The microcomputer 3 determines whether the setting of the frequency has been completed based on the AFT voltage. That is, when the AFT voltage is fluctuating, it is determined that the broadcast station is being searched because the voltage control oscillator 13 is adjusting. On the other hand, when the AFT voltage is constant, since the oscillation frequency of the voltage controlled oscillator 13 is also adjusted to a constant value, it is determined that the search for the broadcast station has been completed, that is, the broadcast station has been detected.

The output of the video intermediate frequency amplification circuit 16 is supplied to a synchronization separation circuit 20, where the horizontal synchronization signal (H sync.) Is separated and supplied to the microcomputer 3. The microcomputer 3 detects whether or not there is a video signal based on the presence or absence of the horizontal synchronization signal, and determines whether or not there is a video signal (SD:
Sync.Detector). That is, when there is a horizontal synchronization signal, it is determined that there is a video signal, and when there is no horizontal synchronization signal, it is determined that there is no video signal.

Next, when the channel is preset, the microcomputer 3 sets an initial value of the frequency f0. The initial value of the frequency f0 is set to a value smaller than the frequency at the lower end of the reception band of any country.
Then, until the broadcast station at the lower end of the reception band is detected,
The frequency f0 is set at a predetermined frequency interval (for example, 0.5 MHz), and a search for a broadcasting station is performed.

In the microcomputer 3, a horizontal synchronizing signal (in other words, S
When the D signal is detected, the AFT search is started at predetermined frequency intervals. That is, the microcomputer 3 monitors the AFT voltage while adding the frequency f0 at predetermined frequency intervals (0.5 MHz), and determines the presence or absence of a broadcasting station. Microcomputer 3
Is determined to be stationery when the AFT voltage is constant,
The T voltage has a predetermined frequency width (usually 2 MHz in the prior art).
If it continues to fluctuate beyond z), it is determined that there is no station.
If it is determined that the station is a station, the channel data of the broadcasting station is preset in the memory 5 and 6 MHz is added to the frequency f0. Therefore, the frequency f0 is set near the frequency of the broadcasting station next to the detected broadcasting station. And again 0.
The frequency f0 is set at 5 MHz, and when the microcomputer 3 detects the horizontal synchronizing signal, the AFT search is executed. By repeating such an operation, the preset can be executed over the entire reception band.

Next, the channel selection operation of the present invention will be described more specifically. FIG. 2 is a drawing showing characteristics of the local oscillation frequency (f (L.Osc)) versus the AFT voltage (control signal) in the local oscillator 13 of the local oscillation circuit. In FIG. 2, when the oscillation frequency of the local oscillator 13 is exactly the reference frequency (fr), the output control signal voltage of the AFT circuit 19 at that time is set as the reference level (Lr) and stored in the memory 5 of the microcomputer 3. The control signal appearing in the area (a) above the reference level (Lr) has a wide range of change in the local oscillation frequency, and this area will be referred to as a first area. The control signal appearing in the area (b) below the reference level (Lr) has a narrow range of change in the local oscillation frequency, and this area will be referred to as a second area. Then, is the output control signal voltage of the AFT circuit 19 in the upper region (a) above the reference level (Lr), or is it equal to the reference level (Lr)?
The microcomputer 3 determines whether or not the area is in the lower area (b).

As shown in FIG. 2, the microcomputer 3 controls the AFT voltage (control signal) when it is in the first area (a) and before it enters the second area beyond the first area. , For example, 8 bits (223.772156KH
The oscillation frequency of the local oscillation circuit 13 is changed in the step of changing the wide frequency change range of z) so as to rapidly approach the reference frequency (fr). On the other hand, if A
When the FT control signal is in the second area (b), for example, one bit (27.965195) is controlled by the microcomputer 3.
By changing the oscillation frequency of the local oscillation circuit 13 in a change step of a narrow frequency change range of (KHz), the local oscillation frequency is finely changed to accurately approach the reference frequency (fr). Thus, the operation is performed at the time of channel selection.

As described above, since the change range of the local oscillation frequency is changed depending on whether the AFT control voltage is above or below the reference level, the frequency of the local oscillator of the local oscillation circuit is set at the time of tuning. Because it quickly approaches the value of
When the frequency change of the local oscillator due to the FT control is rapidly adjusted and the AFT control signal is below the reference level, the oscillation frequency of the local oscillator is changed in a small change range. The frequency of the local oscillator can be accurately controlled.

[0016]

As described above, the TV signal channel selecting apparatus of the present invention changes the local oscillation frequency change range depending on whether the AFT control voltage is above or below the reference level. In the case of a station, since the frequency of the local oscillator of the local oscillator circuit rapidly approaches the reference value, the frequency change of the local oscillator accompanying the AFT control is rapidly adjusted, and the AFT control signal is lower than the reference level. In this case, since the oscillation frequency of the local oscillator is changed in a small change range, the frequency of the local oscillator can be accurately controlled. Therefore, unlike the prior art, the screen that is being reflected does not become a noise screen when selecting a channel.
Moreover, the tuning operation is stabilized and completed in a very short time, which is very effective.

[Brief description of the drawings]

FIG. 1 is a block diagram of a television signal tuning apparatus according to the present invention.

FIG. 2 is a diagram showing characteristics of a local oscillation frequency body AFT control voltage.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 channel selection device 2 channel selection operation unit 3 microcomputer (control unit) 4 latch register 5 memory 6 variable frequency divider 7 phase detector 8 reference oscillator 9 clock pulse generation circuit 10 fixed frequency divider 11 low-pass filter 12 tuner 13 local oscillator Reference Signs List 14 high frequency amplifier 15 mixing circuit 16 video intermediate frequency amplification circuit 17 video signal processing circuit 18 prescaler 19 automatic frequency adjustment (AFT) circuit 20 sync separation circuit

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H03J ^7/ 00-7/18 H04N 5/44

Claims (2)

(57) [Claims] 1. A high-frequency amplifier circuit for amplifying a signal received by an antenna, a local oscillator circuit of a PLL synthesizer type, and a mixing circuit for mixing an output signal of the local oscillator circuit and an output signal of the high-frequency amplifier circuit. , the AFT control signal with to eject the automatic tuning (AFT) control signal of the intermediate frequency carrier signal of an output of the mixing circuit and a frequency detection
Signal to the local oscillation circuit to correct the local oscillation frequency
An AFT circuit, a signal detection circuit for detecting the presence of the reception signal, and a local oscillation frequency of the local oscillation circuit.
AFT control signal generated when the reference frequency is
And the AFT control signal is
When it appears, it is the area above the reference level.
The range of change of the local oscillation frequency by the AFT control signal.
Is larger in the first area or the area below the reference level.
And a change in local oscillation frequency due to the AFT control signal.
The AFT control signal is sent to any of the second areas having a narrow range.
And a control unit for determining whether or not a signal is present. In the state where the local oscillation frequency of the local oscillation circuit is controlled in accordance with a channel selection operation, and the reception signal is detected by the signal detection circuit , the control is performed. The AFT control signal
When the signal is in and over the first area
Wherein the first region when Ete said second region of changing the local oscillation frequency of the local oscillator circuit by a change Tesuppu wide frequency variation range is up first enters Rutotomoni, the AFT control signal is present in the second region Changing the local oscillation frequency of the local oscillation circuit in a change step of a narrow frequency change range which is a fraction of the change step of the AFT.
When the control signal reaches a constant value without fluctuating, the local
A television signal tuning device configured to terminate the control of the vibration frequency . 2. A television signal tuning apparatus according to claim 1, wherein a change range of the local oscillation frequency in said first area is 8 bits, and a conversion range of the local oscillation frequency in said second area is 1 bit.