JPH06314958A - Automatic preset circuit - Google Patents

Abstract

PURPOSE:To realize the automatic preset circuit which identifies a receptible channel from all channels in an on-vehicle television receiver, shortens a time for preset and prevents interference from an adjacent channel. CONSTITUTION:The circuit is provided with a tuner 1 controlling a channel selection frequency with a tuning voltage. Upon the receipt of an IF signal from the tuner 1, a VIF circuit 2 outputs a sigmate characteristic AFT signal to a signal presence discrimination circuit 10. Let a channel selection frequency by (f), the signal presence discrimination circuit 10 discriminates a level of an AFT signal whose frequency is f + or -DELTAf to discriminate whether or not the reception is enable and when enable, a receptible channel number is stored in a memory 8. Then the signal presence discrimination circuit 10 gives a frequency control signal to a tuning voltage generating circuit 7 to implement down-tuning. Thus, automatic preset is finished in several seconds.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention detects a receivable signal from all channels in a television receiver,
The present invention relates to an auto preset circuit that stores a channel number or frequency.

[0002]

2. Description of the Related Art When a vehicle moves in an on-vehicle television receiver, a receivable broadcast channel changes.
For this reason, many vehicle-mounted television receivers have a built-in auto preset (automatic search) circuit.
The auto-preset circuit searches for and stores a receivable channel number in response to the influence of a radio wave condition that changes every moment, and enables automatic channel selection.

An auto preset circuit used in a conventional television receiver will be described with reference to FIG. FIG. 3 is a block diagram showing an example of the overall configuration of a conventional auto preset circuit. In the figure, a tuner 1 amplifies a VHF or UHF radio wave input from an antenna at a high frequency, and also a video signal and an audio signal (TV) of a specific channel.
This is a circuit for selecting (signal).

The tuner 1 comprises a high frequency amplifier circuit 1a, a mixing circuit 1b, a local oscillator circuit 1c and a variable capacitance diode 1d. The mixing circuit 1b inputs the local oscillation frequency obtained by the local oscillation circuit 1c, and outputs an intermediate frequency video signal (IF signal) and an audio signal. The variable capacitance diode 1d constitutes a resonance circuit together with a coil (not shown), and its capacitance is controlled by a tuning voltage generating circuit described later. The VIF circuit 2 is composed of a video intermediate frequency amplification circuit 2a and a video detection circuit 2b. VI
The F circuit 2 inputs the IF signal from the tuner 1, outputs the detected video signal, and outputs the automatic frequency adjustment signal (A
FT signal) is output.

The chroma circuit 3 inputs a baseband video signal from the VIF circuit 2 and outputs a video signal separated into a luminance signal and a chrominance signal to the display circuit 4. The display circuit 4 is a circuit for outputting R, G, B signals to a CRT (not shown). The integrating circuit 5 is a circuit which receives the horizontal synchronizing signal from the chroma circuit 3, integrates it, converts it into an analog signal, and outputs it to the signal presence / absence determining circuit 6. The signal presence / absence judging circuit 6 judges whether the level of the input signal is higher or lower than the reference level, and if it is higher, judges that the TV signal of the set channel can be received, and gives a frequency control signal to the tuning voltage generating circuit 7. Is.

A tuning voltage generating circuit 7 shown by a broken line is a circuit for applying a tuning voltage to the variable capacitance diode 1d of the tuner 1, and is composed of a tuning voltage control circuit 7a and a tuning voltage holding section 7b. When the frequency control signal is input from the signal presence / absence determination circuit 6, the tuning voltage control circuit 7a is a circuit that generates a tuning pulse of a specific channel and outputs a PWM signal or a PNM signal. This signal is given to the tuning voltage holding unit 7b. Then, the tuning voltage control circuit 7a inputs a signal from the local oscillation circuit 1c and controls the tuning pulse so that the tuning frequency becomes stable.

The tuning voltage holding unit 7b is composed of a circuit including a transistor Q1, a capacitor C1, resistors R1 and R2. In the transistor Q1, the base is connected to the collector via the capacitor C1, and the collector is connected to the control terminal of the variable capacitance diode 1d. When a pulse for charging is applied to the base through the resistor R1, the transistor Q1 charges the tuning voltage generating capacitor C1 from the power source B through the resistor R2. Then, a constant tuning voltage is held in the collector.

The memory 8 has channels 1 to 62c.
It is a circuit for storing all the frequencies of the TV broadcast that can be tuned in h and holding data for giving a frequency control signal for searching through the signal presence / absence determination circuit 6 at the time of tuning. Further, the memory 8 functions to store a receivable channel number when the tuner 1 receives a TV signal that can be received and the signal presence / absence determination circuit 6 inputs an analog signal of a reference level or higher.

The operation of the auto preset circuit thus configured will be described. 62 in VHF and UHF bands
To search for a receivable channel from the channel band, first, the tuning voltage generation circuit 7 outputs a tuning voltage corresponding to the channel station having the lowest frequency. When this tuning voltage is applied to the variable-capacitance diode 1d, the local oscillator circuit 1c oscillates by 58.75 MHz higher than the tuning frequency and applies it to the mixing circuit 1b. At this time, the mixing circuit 1b inputs the TV signal of the tuning frequency from the high frequency amplification circuit 1a, takes a beat with the output signal of the local oscillation circuit 1c, and gives an IF signal of 58.75 MHz to the VIF circuit 2.

Next, the VIF circuit 2 amplifies the input 1F signal by the video intermediate frequency amplification circuit 2a, and the video detection circuit 2b.
The TV signal detected by is supplied to the chroma circuit 3. The chroma circuit 3 separates the luminance signal and the chrominance signal from the composite video signal and further extracts the horizontal synchronizing signal. Integration circuit 5
When the horizontal synchronizing signal is input from the chroma circuit 3, the signal is integrated for a certain period of time and converted into an analog signal.

The signal presence / absence determining circuit 6 determines that the broadcast program can be received at the currently selected frequency if the input signal is at a certain level or higher, and stores the receivable channel number in the memory 8. Next, the signal presence / absence determining circuit 6 increments the number of channels and supplies a frequency control signal to the tuning voltage generating circuit 7 to raise the tuning voltage. In this case, the tuning voltage control circuit 8 gives the next tuning pulse to the transistor Q1. Then, when the transistor Q1 is off, the capacitor C1 is charged from the power source B through the resistor R2.

Also in the case of channel selection, the integrating circuit 5 inputs the horizontal synchronizing signal and gives an analog signal to the signal presence / absence determining circuit 6. The signal presence / absence determination circuit 6 determines that there is no broadcast if no radio wave of a specified level is received at the currently selected frequency, and outputs a frequency control signal for increasing the selected frequency to the tuning voltage control circuit 8. As described above, from 1ch to 6
The channel selection frequency is increased to 2ch (up search), and the receivable channel number at the current position of the vehicle is stored.

[0013]

However, in the above-mentioned conventional configuration, from the generation of the tuning voltage by the tuning voltage generation circuit 7 to determine the presence / absence of the TV signal until the signal presence / absence determination circuit 6 outputs the result. Was taking time. That is, there is a problem that it takes time for the chroma circuit 3 to output the horizontal synchronizing signal, and when the signal is integrated by the integrating circuit 5, it takes additional time for obtaining an analog signal.

In addition, in order to up-search a channel having a high frequency, it is necessary to increase the tuning voltage every time the channel is moved up in the same frequency band.
That is, in order to set the output voltage of the tuning voltage generating circuit 7 to a desired value, the charging time of the time constant determined by the capacitor C1 and the resistor R2 is required. Therefore, it takes, for example, 15 to 20 seconds to determine the presence / absence of signals on all channels and store the receivable channel numbers.

Further, according to the level obtained by integrating the horizontal synchronizing signal, T
Since the presence / absence of the V signal is determined, if there is a strong signal in the adjacent channel, the signal presence / absence determination circuit 6 may malfunction as having a signal even if there is no TV signal in the currently selected channel.

The present invention has been made in view of such conventional problems, and until the signal levels of all channel signals are automatically determined in the television receiver and the receivable channel numbers are stored. It is an object of the present invention to realize an auto-preset circuit that shortens the time of, and reduces the influence from adjacent channels.

[0017]

According to the invention of claim 1 of the present application, a tuning voltage is inputted and T of a specific channel is inputted.
The tuner that selects the V signal and the TV signal of the intermediate frequency from the tuner are input, the signal is detected, and the output level is S-shaped or inverse S in the low and high frequencies centering on the selected frequency. VIF circuit that outputs an automatic frequency adjustment (AFT) signal having a character characteristic, a memory that stores a channel number or frequency that can be selected and a receivable channel, and a low frequency band that is a constant frequency away from the center frequency of channel selection. When the AFT signal obtained from the VIF circuit is input on the high frequency side, and one of the AFT signals on the low frequency side and the high frequency side both exceeds the first reference value and the other becomes the second reference value or more, reception is possible. Judgment, giving a channel number to the memory, and a signal presence / absence judgment circuit that outputs a frequency control signal necessary for channel selection,
A frequency control signal is input from a signal presence / absence determination circuit, a tuning voltage generation circuit that causes a capacitor for tuning voltage generation to hold a specified tuning voltage and outputs the voltage to a tuner is characterized by being provided. is there.

According to a second aspect of the present invention, the signal presence / absence determining circuit, when searching for a receivable broadcast channel, reads the channel numbers from the memory in descending order of frequency. is there.

[0019]

According to the first aspect of the present invention having such a feature, the signal presence / absence determining circuit provides the tuning voltage generating circuit with the frequency control signal required for channel selection. Then, the tuner inputs a tuning voltage and selects a TV signal of a specific channel. On the other hand, the VIF circuit inputs an intermediate frequency TV signal from the tuner, detects the signal, and
An automatic frequency adjustment (AFT) signal whose output level has an S-shaped characteristic or an inverse S-shaped characteristic around the tuning frequency is output. When the AFT signal is input to the signal presence / absence determination circuit, the AF in the low frequency band and the high frequency band separated from the center of the tuning frequency by a constant frequency.
When one of the T signals exceeds the first reference value and the other becomes equal to or less than the second reference value, it is determined that reception is possible. If it can be received, the channel number is stored in the memory. If the signal cannot be received, the tuning voltage generation circuit inputs the next frequency control signal from the signal presence / absence determination circuit, and causes the capacitor for tuning voltage generation to hold the specified tuning voltage. In this way, the auto preset of the selected channel is performed in a short time.

According to the invention of claim 2 of the present application, in addition to the operation of the invention of claim 1, the signal presence / absence judging circuit reads out the channel selectable channel numbers from the memory in descending order from the highest frequency ( Down tuning). Therefore, the search time for the receivable broadcast channel is shortened as compared with the up tuning.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A tuning circuit according to an embodiment of the present invention will be described with reference to FIG. In FIG. 1, the auto preset circuit is provided with a tuner 1, a VIF circuit 2, a chroma circuit 3, a display circuit 4, a tuning voltage generating circuit 7, and a memory 8, respectively, which is the same as the conventional example. Omit it. Unlike the conventional example, a signal presence / absence determining circuit 10 is provided between the VIF circuit 2 and the tuning voltage generating circuit 7. The AFT circuit 2c in the VIF circuit 2 has an FM detection unit (not shown), receives the IF signal amplified from the video intermediate frequency amplification circuit 2a, and uses the discriminator to generate the inverse S-shaped AFT signal. It is a circuit to generate. The signal presence / absence determination circuit 10 is a circuit that receives the automatic frequency adjustment signal (AFT signal) from the AFT circuit 2c and determines the signal amplitude level thereof. That is, the signal presence / absence determination circuit 1
0 is a constant frequency deviation Δf from the center frequency f (for example, 20), where f is the center frequency of the specific channel to be selected.
(0 KHz), the AFT signal level is discriminated in a portion separated by high or low frequencies to obtain an AFT signal exceeding the first reference value at one of the frequencies of f ± Δf and the second reference at the other. When an AFT signal equal to or less than the value is obtained, it is determined that reception is possible.

The frequency control signal output from the signal presence / absence determining circuit 10 is given to the tuning voltage control circuit 7a in the tuning voltage generating circuit 7, and the receivable channel number is given to the memory 8. The tuning pulse output from the tuning voltage control circuit 7a is a PWM or PNM pulse as in the conventional example.

The operation of the auto-preset circuit of the present embodiment thus constructed will be described with reference to the characteristic diagram of FIG. FIG. 2 shows the characteristics of the AFT signal output from the ATF circuit 2c in the VIF circuit 2.
Regarding the input / output characteristics of the FM detection section, the output level changes in an inverted S shape around the tuning frequency f as the center.

If the oscillation frequency of the local oscillator circuit 1c shifts to the lower side, the frequency of the IF signal output from the tuner 1 shifts to the lower side than the normal value, and the level of the AFT signal rises. When this signal is given to the variable capacitance diode 1d via the transistor Q1 of the tuning voltage generation circuit 7, the capacitance of the variable capacitance diode 1d decreases. Therefore, the frequency of the local oscillation circuit 1c is corrected to the higher side and always kept at the correct frequency.

In order to automatically search the broadcast frequency, the frequency of each channel must be read out from the memory 8 in order. First, the tuning voltage control circuit 7a is the memory 8
Read the highest frequency channel number from
A frequency control signal corresponding to + Δf is given to the tuning voltage control circuit 7a. The tuning voltage control circuit 7a applies a tuning pulse to the transistor Q1, charges the capacitor C1 so that the tuning voltage of the channel station having the highest frequency is obtained, and applies a desired tuning voltage to the variable capacitance diode 1d.

The tuner 1 outputs the IF signal to the VIF circuit 2. When the VIF circuit 2 outputs the AFT signal as shown in FIG. 2, the signal presence / absence determination circuit 10 determines the magnitude of the signal amplitude. That is, the signal presence / absence determination circuit 10 is f + 200K.
The signal level in Hz is detected, and the value is set to Lb. Next, the signal presence / absence determination circuit 10 gives a frequency control signal corresponding to f-200 KHz to the tuning voltage control circuit 7a. The tuning voltage control circuit 7a slightly discharges the electric charge of the capacitor C1 so that the tuning voltage becomes f-200 KHz.

The signal presence / absence determining circuit 10 sets the level of the AFT signal output by the VIF circuit 2 at f-200 KHz to La. At this time, the signal presence / absence determination circuit 10 determines that the signal can be received when the signal level La is higher than the reference level Lc and the signal level Lb is lower than the reference level Ld. If the signal is receivable, the signal presence / absence determination circuit 10 stores the channel number currently selected in the memory 8.

Next, the tuning channel number is decremented, and the tuning voltage control circuit 7a gives a corresponding tuning pulse to the transistor Q1. Also at this time, the electric charge of the capacitor C1 is rapidly discharged through the collector-emitter of the transistor Q1 and set to a predetermined tuning voltage. In this case, the signal level La at f-200KHz is lower than the reference level Lc, or f + 200K
If the signal level Lb in Hz is higher than the reference level Ld, the signal presence / absence determination circuit 10 determines that reception is impossible, and searches for the next channel.

As described above, down tuning is performed from 62 ch to 1 ch, and receivable channel numbers are sequentially registered in the memory 8. When the auto preset is performed by such a method, the time required for the automatic search of all channels is completed in a short time of, for example, 3 seconds to 5 seconds as shown in FIG. Further, since the presence or absence of the TV signal is determined by the AFT signal, the level of the AFT signal at the search frequency f ± Δf does not increase even if there is a signal in the adjacent channel, and the signal presence / absence determination circuit 10 does not malfunction.

In this embodiment, the frequency for determining the presence / absence of the TV signal is set to f ± 200 KHz, but it may be other than this value.
The frequency difference between the direction and the − direction may not be the same.

[0031]

As described above in detail, according to the present invention, by using the AFT signal, the AFT signal level at two points, that is, a frequency higher and a frequency lower than the tuning frequency by a certain constant frequency, is checked. The presence / absence determination circuit can accurately determine the presence / absence of a TV signal. Then, the search is started from the highest frequency channel, the channel numbers are sequentially decreased, and the downsearch is performed to the lowest frequency channel, so that the receivable channels are determined at high speed from all the channels and stored. You can
Further, the effect of reducing erroneous determination due to TV signals of adjacent channels can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an auto preset circuit according to an embodiment of the present invention.

FIG. 2 AF in the auto preset circuit of the present embodiment
It is a characteristic view of a T signal.

FIG. 3 is a block diagram showing a configuration example of a conventional auto preset circuit.

FIG. 4 is an explanatory diagram showing a time required for auto preset.

[Explanation of symbols]

 1 Tuner 1a High Frequency Amplifier Circuit 1b Mixing Circuit 1c Local Oscillation Circuit 1d Variable Capacitance Diode 2 VIF Circuit 2a Video Intermediate Frequency Amplifier Circuit 2b Video Detection Circuit 2c AFT Circuit 3 Chroma Circuit 4 Display Circuit 7 Tuning Voltage Generation Circuit 7a Tuning Voltage Control Circuit 7b Tuning voltage holding unit 10 Signal presence / absence determination circuit Q1 transistor R1, R2 resistance C1 capacitor B power supply

Claims (2)

[Claims] 1. A tuner for inputting a tuning voltage to select a TV signal of a specific channel, and an intermediate frequency TV signal from the tuner for input and detection of the signal, and centering on the selected frequency. A VIF circuit that outputs an automatic frequency adjustment (AFT) signal whose output level has an S-shaped characteristic or an inverse S-shaped characteristic on the low frequency side and the high frequency side, and a channel number or frequency that can be selected and a receivable channel are stored. Input the memory and the AFT signal obtained from the VIF circuit in the low frequency band and high frequency band apart from the tuning center frequency by a constant frequency,
When both the AFT signals on the low-frequency side and the high-frequency side exceed the first reference value and the other exceeds the second reference value, it is determined that reception is possible, a channel number is given to the memory, and channel selection is performed. A signal presence / absence determination circuit that outputs a frequency control signal required for, and a frequency control signal is input from the signal presence / absence determination circuit,
An auto-preset circuit, comprising: a tuning voltage generating circuit that holds a specified tuning voltage in a tuning voltage generating capacitor and outputs the voltage to the tuner. 2. The signal presence / absence determining circuit, when searching for a receivable broadcast channel, reads channel numbers from the memory in descending order of frequency. Preset circuit.