JPH09261547A - Television channel selector of voltage synthesizer system and selection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a lock range of a frequency for each channel constant by calculating a tilt of a tuning voltage for each channel and limiting the tuning voltage depending on the tilt. SOLUTION: In the operation of an automatic tuning memory(ATM), a microcomputer 32 receives a synchronization discrimination result from a synchronization discrimination circuit 30 to detect a start position of presence of a station. Furthermore, the microcomputer 32 monitors an S-curve voltage and compares the S-curve voltage with a reference voltage and then calculates a tuning voltage (PWM value) corresponding to a frequency change from the start of station presence till the S-curve voltage reaches the reference voltage for each channel. The tuning voltage is converted into a voltage equivalent to a prescribed lock range (e.g. ±2MHz) and the lock range is limited by using the voltage in the operation of AFC.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage synthesizer type channel selecting apparatus and channel selecting method, and in particular, it is obtained by FM detection of an intermediate frequency signal of a video signal in a television receiver, a VTR or a VCR. The present invention relates to a voltage synthesizer type television tuning apparatus and a tuning method for adjusting a local oscillation frequency based on a voltage (AFC voltage) corresponding to a deviation amount of the local oscillation frequency.

[0002]

2. Description of the Related Art A conventional voltage synthesizer type tuning device of this type first increases a tuning voltage (control voltage) for adjusting a local oscillation frequency from a minimum voltage to reach a correct tuning point. At this time, the tuning information (tuning voltage, band switching voltage) is stored in a memory (eg, EEPROM). A so-called auto tuning memory (ATM) is performed. That is, FIG. 4 (A)
And (B), S curve voltage (detection voltage) proportional to the frequency deviation obtained from the intermediate frequency signal of the video signal
And the result of discrimination of synchronization (localized or non-localized) by the composite synchronous signal is monitored, and when it is local and the S curve voltage is the central voltage (B in FIG. 4), the channel is synchronized. Information is stored in the memory. Then, during normal operation, the above-mentioned tuning information read from the memory is applied to the tuner and received.

At this time, in order to maintain the local oscillation frequency at a correct value, the control voltage (tuning voltage) is finely adjusted (AFC: automatic) so that the S curve voltage is always the center (reference) voltage (B in FIG. 4). Frequency control) to pull in the frequency. That is, for example, when the S-curve voltage changes from the region B in FIG. 4 to the region C in FIG. 4 due to ambient temperature, change with time, or the like, the control voltage data (P
The WM value) is decreased, and on the other hand, when the value changes to the area A in FIG. 4, the PWM value is increased and the local oscillation frequency is corrected to a correct value.

[0004]

In such a channel selecting apparatus, a station which is determined to be a station during the ATM operation stops transmission due to a station failure or a temporary interruption of broadcasting. If so, the AFC operation may be performed according to the S-curve voltage, and as a result, the next stationed channel may be operated. Therefore, conventionally, the tuning voltage is limited to regulate the pull-in range.

However, since the tuning voltage and the local oscillating frequency have the characteristics shown in FIG. 5, there is a problem in that even if the tuning voltage and the local oscillation frequency are in the same band, a large difference occurs in the pull-in amount due to the difference in the tuning voltage. That is, for example, in a channel in which the frequency change with respect to the tuning voltage is small, if the frequency pull-in range is set to ± 2 MHz,
For channels with large frequency changes, the pull-in range is ± 1
It may be 0 MHz. Therefore, the occupied bandwidth per channel (Japan: 6MHz, Europe: 7or8MH
This results in pulling up to the adjacent channel as seen from z). In order to solve this problem, it is possible to change the pull-in range according to the tuning voltage, but it is difficult and uneconomical to realize from the viewpoint of compatibility.

Therefore, a main object of the present invention is to provide a voltage synthesizer type channel selecting apparatus and a channel selecting method which can realize accurate frequency pulling in simply and inexpensively.

[0007]

A first invention is a voltage synthesizer system for generating a control voltage for adjusting a local oscillation frequency according to a detection voltage proportional to a frequency deviation generated from an intermediate frequency signal of a video signal. A television channel selection device, detecting means for detecting the station start position from the synchronization determination result of the channel determined based on the detection voltage, comparing means for comparing the detection voltage and the reference voltage, and station start A calculation means for calculating, for each channel, a control voltage corresponding to a predetermined pull-in amount of the local oscillation frequency based on the position and the comparison result in the comparison means is provided, and the pull-in amount of the local oscillation frequency in each channel is calculated by the calculated control voltage. A voltage synthesizer type television channel selection device characterized in that it is always constant.

A second aspect of the present invention is a television channel selection method using a voltage synthesizer system for generating a control voltage for adjusting a local oscillation frequency according to a detection voltage proportional to a frequency deviation generated from an intermediate frequency signal of a video signal. Therefore, the station start position is detected from the synchronization determination result of the channel determined based on the detected voltage, the detected voltage is compared with the reference voltage, and the detected voltage from the station start until the detected voltage becomes equal to the reference voltage. A television channel selection method that detects the amount of change in the control voltage, calculates a voltage according to a predetermined pull-in amount of the local oscillation frequency for each channel from the amount of change, and controls the local oscillation frequency with the calculated voltage. is there.

[0009]

In ATM, the start position of the station is detected from the judgment result of the station non-station of the channel based on the composite synchronizing signal. Then, the amount of change in the control (tuning) voltage during the period from the start of the local station to the detection (S curve) voltage becoming the reference (center) voltage is detected. A voltage corresponding to a predetermined frequency pull-in range is calculated from the tuning voltage for each channel, and the local oscillation frequency is adjusted by the voltage, so that the frequency pull-in range in each channel is always constant.

[0010]

According to the present invention, since the slope of the tuning voltage is calculated for each channel and the tuning voltage is limited according to the slope, the frequency pull-in range in each channel can be made constant. The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description of embodiments with reference to the drawings.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, a channel selection device 10 of this embodiment.
Detects the phase shift of the video signal according to the S-curve voltage (detection voltage) generated from the intermediate frequency signal of the video signal, and determines the local oscillation frequency with the tuning voltage (control voltage) corresponding to the phase shift amount. It controls to the correct value. That is, the television high-frequency signal from the antenna (not shown) is amplified by the high-frequency amplifier circuit 14 of the tuner 12 and then, in the mixing circuit 16, is 58.75 M higher than the video carrier frequency of the channel selected from the local oscillation circuit 18.
The intermediate frequency signal is extracted by mixing it with the local oscillation frequency signal higher than Hz.

After the band characteristic of the intermediate frequency signal is changed by the surface acoustic wave filter 22 of the video intermediate frequency amplifying circuit 20 in the subsequent stage, the gain is controlled by the amplifying circuit (IF-IC) 24. The amplified signal is detected by the video detection coil 26, and the composite video signal is extracted. Further, the S-curve voltage detection coil 28 extracts the S-curve voltage. The detected composite video signal is sync-separated in the sync discriminating circuit 30, and it is judged from the composite sync signal obtained as a result whether or not there is broadcasting on the channel (stationed) or not (stationless). This synchronization determination result is given to the microcomputer 32 together with the S curve voltage.

By receiving the S-curve voltage, the microcomputer 32 performs PWM according to the frequency shift amount of the local oscillation frequency.
Output the value. That is, the amplifier circuit 24 FM-detects the video intermediate frequency signal and smoothes it by an integrating circuit (not shown).
An FC (automatic frequency control) circuit 34 is included. Therefore, AF
The C circuit 34 outputs a DC voltage corresponding to the frequency deviation from the intermediate frequency, that is, an S curve voltage. As a result, the microcomputer 32 outputs a PWM value (voltage data) that corrects the deviation. This PWM value is LPF36
After being demodulated to a tuning voltage (control voltage) by, it is given to the local oscillation circuit 18 and the local oscillation frequency is adjusted to a regular value. That is, the tuning device 10 has a digital AFC function.

The microcomputer 32 also receives the above-mentioned synchronization determination result, and the synchronization determination result is local at the time of ATM (auto tuning memory) operation, and the S curve voltage is the reference (center) voltage. At that time, it is determined that there is broadcasting on that channel (stationed), and tuning information such as tuning voltage and band switching voltage at that time is recorded in the EEPROM 38. Then, the normal operation (AF
At the time of C), the tuning information is read from the EEPROM 38, applied to the tuner 12, and received.

At the time of ATM, the microcomputer 32 is further added.
Detects the start position of the stationed area indicated by the arrow from the synchronization determination signal shown in FIG. Then, the variable (count up or down) speed of the tuning voltage (PWM value) is delayed to search the center (reference) voltage of the S curve voltage shown in FIG. 4 (A). Then, the tuning voltage corresponding to the frequency change from the start of the stationing until the S-curve voltage becomes the central voltage is obtained for each channel, and the local oscillation circuit 18 is controlled by the tuning voltage at the time of AFC. That is, the amount of frequency change from the start of the station shown in T of FIG. 4 (B) to the center voltage of the S curve voltage is determined by the surface acoustic wave filter 22, the amplification circuit 24, and the video detection coil 26, and is assigned to the channel. Regardless of this, it shows a substantially constant value. Utilizing this characteristic, a tuning voltage corresponding to a pull-in range of a predetermined frequency (generally ± 2.0 MHz) is obtained from the tuning voltage corresponding to a constant frequency calculated for each channel, and pulling in the local oscillation frequency with the tuning voltage. Do. Therefore, the frequency pull-in range can be kept constant (± 2.0 MHz) regardless of the channel.

The details will be described below with reference to the flow charts of FIGS. 2 and 3. That is, during ATM operation, as shown in FIG.
When the N (N is a natural number) channel is designated in step S1, the memory (not shown) storing the flag indicating the synchronization determination result or the PWM value is initialized in step S3. In other words, a flag indicating that there is no station is set,
The PWM value of the memory is reset (= 0). And
In step S5, 1 is added to the PWM value,
The local oscillation frequency is controlled by the PWM value, that is, the tuning voltage, and the video signal is received. Subsequent step S7
In step 2, it is determined from the composite sync signal of this video signal that there is no station, and if there is no station, the process returns to step S5 and the PWM value is incremented (PWM + 1).
On the other hand, if it is determined that the station is present, step S9
Then, the PWM value (V1) at that time is recorded in the memory. That is, the start position of the station is detected.

In the following step S11, the PWM value is further incremented, and it is determined in step S13 whether the S-curve voltage at that time is equal to or lower than the reference voltage. That is, the S-curve voltage is the reference (center)
The PWM value is incremented until the voltage is reached. Then, when the S curve voltage becomes equal to or lower than the reference voltage, the PWM value (V2) at that time is recorded in the memory in step S15. That is, when the S-curve voltage is equal to or lower than the voltage X in FIG. 4A, the PWM value (tuning voltage) at that time is stored. That is, the position (frequency) at which the S curve voltage becomes the reference (center) voltage is detected.
Therefore, the constant frequency indicated by T in FIG. 4B can be obtained from the above-described PWM values (V1 and V2).

In a succeeding step S17, a variable voltage corresponding to a pulling range of a predetermined frequency is calculated based on the PWM values (V1 and V2) recorded in the memory.
That is, the value obtained by subtracting V1 from V2 (V2-V1)
The variable voltage (V3) corresponding to the pull-in range can be calculated by multiplying the pull-in range (for example, 2 MHz) of the predetermined frequency by a value (quotient) obtained by dividing the pull-in range by a constant frequency (T: for example, 1.5 MHz). Calculated variable voltage (P
The WM value) is recorded in the memory in step S19. Further, this variable voltage is recorded in the EEPROM 38 as with the tuning voltage and is used as a limiter during the digital AFC operation. Then, in step S21, it is determined whether or not the N channel is the maximum channel, and if the result is "NO", 1 is added to N in step S23, and the above-mentioned step S1 is performed for each channel up to the maximum channel. The process from to step S19 is repeated. That is, the ATM operation is completed.

During the AFC operation, the EEPROM 38
The tuning information such as the tuning voltage recorded in is read and received according to the tuning information. That is, FIG.
When the digital AFC operation mode is designated, the PWM value (V2) is read from the memory in step S25. In other words, at the time of ATM operation, the PWM value when the correct tuning point is reached is read from the memory,
In step S27, tuning is performed according to the PWM value. In the following step S29, it is determined whether the tuning voltage corresponding to the PWM value can be corrected by the variable voltage calculated in step S17 of FIG. That is, it is determined whether or not the calculated variable voltage can absorb the fluctuation of the S-curve voltage due to temperature or change with time. Then, if it is within the limit range, in step S31, the S curve voltage is compared with the reference voltage, and the S curve voltage is Y in FIG.
If it is smaller than the above, the PWM value is decremented by 1 and finely adjusted in the direction of decreasing the PWM value. On the other hand, when the S-curve voltage is higher than X in FIG. 4A, conversely, 1 is added to the PWM value. When the S curve voltage indicates the reference voltage (Y ≦ S curve voltage ≦ X),
Returning to step S27, tuning is performed again.

Thus, paying attention to the fact that the tuner local range characteristics in the same amplifier circuit 24 are substantially constant,
Variable (tuning) to allow the frequency pull-in range
Since the voltage (slope) is calculated for each channel and the local oscillation frequency is controlled by the variable voltage, the frequency pull-in range can be kept constant. Therefore, it is possible to easily and accurately apply the pull-in restriction.

[Brief description of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention.

FIG. 2 is a flowchart showing an ATM operation of the embodiment shown in FIG.

FIG. 3 is a flowchart showing the AFC operation of the embodiment in FIG.

FIG. 4 is a waveform diagram showing an S curve voltage and a synchronization determination signal.

FIG. 5 is a graph showing characteristics of tuning voltage and local oscillation frequency.

[Explanation of symbols]

 10 ... Tuning device 12 ... Tuner 18 ... Local oscillation circuit 16 ... First switch 20 ... Video intermediate frequency amplification circuit 24 ... Amplification circuit 30 ... Sync discrimination circuit 32 ... Microcomputer 34 ... AFC circuit

Claims (2)

[Claims] 1. A television channel selection apparatus of a voltage synthesizer system for generating a control voltage for adjusting a local oscillation frequency according to a detection voltage proportional to a frequency deviation generated from an intermediate frequency signal of a video signal, wherein: Detection means for detecting the station start position from the synchronization determination result of the channel determined based on the detection voltage, comparison means for comparing the detection voltage with a reference voltage, and comparison in the station start position and the comparison means Based on the result, a calculation means for calculating the control voltage corresponding to a predetermined pull-in amount of the local oscillation frequency for each channel is provided, and the pull-in amount of the local oscillation frequency in each channel is always constant by the calculated control voltage. A voltage synthesizer type television channel selection device characterized in that 2. A television channel selection method using a voltage synthesizer system for generating a control voltage for adjusting a local oscillation frequency according to a detection voltage proportional to a frequency deviation generated from an intermediate frequency signal of a video signal, comprising: a) detecting the station start position from the synchronization determination result of the channel determined based on the detection voltage, (b) comparing the detection voltage and a reference voltage, (c) the detection voltage from the station start to the detection voltage. Detecting the amount of change in the control voltage until becomes equal to the reference voltage, (d) calculating the voltage corresponding to the predetermined pull-in amount of the local oscillation frequency for each channel from the amount of change, and (e) A television tuning method, wherein the local oscillation frequency is controlled by the calculated voltage.