JPS59126314A - Automatic tuning device of on-vehicle television receiver - Google Patents

Abstract

PURPOSE:To listen to the same program continuously without manual operation by providing a table which contains reception frequency information on every network of the same affiliate, and a microprocessor which searches this table for reception frequency information and determining a reception frequency. CONSTITUTION:An AM detection output V drops to a reference voltage V0 at a limit of a service area during movement over the reception of a specific UHF channel ch.A. When this drop period T exceeds reference pulse width T0 (e.g. 5-6sec), the MPU (microprocessor) 15 is started by the output S of a pulse width comparator 13. Consequently, the MPU15 starts accessing the table 16 and the receiver enters a search state. This access to the table 16 by the MPU15 starts at a station which is at short distance to the station ch.A being received at present and belongs to the network of the same affiliate. When the MPU15 reads one frequency division ratio N out of the table 16, the reception frequency varies. Consequently, a tuning detection part 17 detects an intermediate frequency signal having a level higher than a specific level and sends a search stop signal to the MPU15.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic tuning device that allows a moving vehicle-mounted television receiver to continuously receive the same program.

The service area for UHF TV radio wave transmission is generally several tens of kilometers from the transmitting station, and channels (frequency bands) are assigned depending on the region, so when traveling with a TV receiver installed in a vehicle, Even if a channel is being received, the reception condition deteriorates within a short period of time, and re-tuning becomes necessary. Furthermore, preset tuning, which is effective for radio receivers, is not effective for television broadcasting where the service area is narrow, and there is the inconvenience of having to re-set the presets frequently, especially when moving in a vehicle.

The present invention enables an in-vehicle TV receiver to automatically search for other channels in the same network to always receive the same program when the electric field of the channel being received falls below the lower level for a certain period of time. It is.

The present invention provides an automatic tuning device that automatically switches to another station when the electric field of the receiving station drops below a certain value during reception by an electronically tuned in-vehicle television receiver that is mounted on a vehicle and moves. a table storing reception frequency information for each network in the series; a microprocessor that searches the table for the reception frequency information and determines the reception frequency; and a circuit that detects the level of the video intermediate frequency signal;
a voltage comparison circuit that compares the level with a reference level; a time comparison circuit that activates the microprocessor when the level of the video intermediate frequency signal is below the reference level for a certain period of time; a tuning detection circuit that stops the search by the microprocessor when a video intermediate frequency signal of a predetermined level or higher is detected;
The feature is that the processing is performed with priority given to those within the same network, and this will be explained in detail below with reference to the illustrated embodiment.

FIG. 1 is a block diagram showing one embodiment of the present invention.
is an antenna, 1 is a high frequency amplifier, 2 is a frequency mixer, 3
is a video intermediate frequency amplifier, 4 is a video detector, 5 is a demodulation output section, 6 is a CRT (cathode ray tube), 7 is a local oscillator, 8 is a PLL (phase locked loop), and 9 is an LPF (low pass filter). These constitute an electronically tuned television receiver. P L L 8 is the product of the reference frequency fr of the crystal oscillator and the given frequency division ratio N (frXN)
and the output frequency f1 of the local oscillator 7. An error output is generated according to the difference between the two and the LPF9 output becomes the tuning voltage.

Therefore, when the frequency division ratio N is changed, the local oscillation frequency fL changes so that frX N = fL, and the center frequency of the tuning circuit included in the high frequency amplifier 1 is determined by adding or subtracting the video intermediate frequency from f. The value will be changed to the specified value.

In this example, the frequency division ratio N given to PLL8 is changed as appropriate to continuously receive the same program. Circuits 10 to 17 within the dashed line frame make this possible. 10 is an AM detector that detects the level of the video intermediate frequency signal from the video intermediate frequency amplifier 3; 11 is the output of the AM detector 10 (DC voltage according to the amplitude of the intermediate frequency signal) and the output of the reference voltage generator 12; (Reference voltage) Vo and compare it with V
<V.

It is a voltage comparator that produces an output T when . This reference voltage Vo is set at the side where the AM detection output (2) drops sharply, as shown in FIG. Reference numeral 13 denotes a pulse width comparison circuit that compares the output T with the output (reference pulse width) To of the reference pulse width generator 14, and when T>To, it provides a search command signal S to the MPU (microprocessor) 15. 16 is a table using ROM (read-only memory), as shown in Fig. 4, receiving frequency information (
In this example, data of frequency division ratio N) is stored.

The operation will be explained below with reference to FIG.

I am currently moving while receiving UHF specific station ch, A.
When the limit of the service area is reached, the AM detection output V drops below the reference voltage Vo. And this period of decline T
When the pulse width exceeds the reference pulse width To (for example, 5 to 6 seconds), the MPUI 5 is activated by the output S of the pulse width comparator 13.

As a result, the MPU 15 starts accessing the table 16, and the receiver enters a search state. Access to the table 16 by the MPU 15 starts from another station that is close in distance to the currently receiving station ch, A, and that belongs to the same network network. For this purpose, N-value data of nearby broadcasting stations are arranged in advance in order of address. For example, if ch and A are being received on the xxTV broadcast system in Figure 4, ch and E are being received.
Or ch, B is the next selected station. MPU15
When the user reads out one frequency division ratio N from the table 16, the receiving frequency changes accordingly. As a result, if the tuning detection section 17 detects an intermediate frequency signal of a predetermined level or higher, the MP
A search stop signal is sent to U15, but until this signal is output, the MPU 15 searches for table 16 at regular intervals.
access. In this case, the next accessed station is c
At h and B, if the tuning detection section 17 outputs a search stop signal at that time, the series of searches will be stopped.

In this way, even if you switch channels within the same network, the broadcast content is generally the same, so listeners of this TV receiver can continue listening to the same program without being aware of it. . However, if the search within the network is exhausted, the program may be transferred to another network, so in this case the program may change, but it may still be better than not being able to receive it. Note that, as shown in FIG. 3, even if the AM detection output temporarily drops below Vo (less than To), the search does not start. This is because in a vehicle-mounted television receiver, there is a strong possibility that this type of momentary interruption will occur due to obstacles such as buildings.

As described above, according to the present invention, when an in-vehicle TV receiver is mounted on a vehicle such as a car and moved, even if the service area of the broadcasting station changes, as long as it is within the same network, the received electric field is automatically adjusted. Since the station with the strongest value is selected, you can continue listening to the same program without performing manual operations.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is an explanatory diagram of the reference voltage used to determine the decrease in the received electric field, Fig. 3 is a waveform diagram used to explain the operation of Fig. 1, and Fig. 4 The figure is an explanatory diagram of Cheagle. In the figure, 10 is an AM detector (level detection circuit), 11 is a voltage comparator, 13 is a pulse width comparison circuit (time comparison circuit),
15 is a microprocessor, 16 is a table, and 17 is a tuning detection circuit. Applicant Fujitsu Ten Ltd. Representative Patent Attorney Minoru Aoyagi 7- Dota,〉

Claims (1)

[Claims] An automatic tuning device that automatically switches to another station when the electric field of the receiving station drops below a certain value while receiving an electronic in-vehicle television receiver that is mounted on a vehicle and moves, a table storing reception frequency information for each network; a microprocessor that searches the reception frequency information from the table and determines the reception frequency;
a circuit for detecting the level of the video intermediate frequency signal; a voltage comparison circuit for comparing the level with a reference level; and activating the microprocessor when the level of the video intermediate frequency signal is below the reference level for a certain period of time. It is equipped with a time comparison circuit and a synchronization detection circuit that stops the search by the microprocessor when a video intermediate frequency signal of a predetermined level or higher is detected during the search by the microprocessor. An automatic tuning device for an in-vehicle television receiver, characterized in that the automatic tuning device is configured to give priority to the following.