JPS6282811A - automatic channel selection device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an automatic channel selection device for a television receiver or the like.

Conventional technology There have been television receivers equipped with electronic tuners.Electronic tuner tuning devices can be roughly divided into two types: direct input type, in which the channel of the station to be received is directly input, and There is a scanning method that automatically scans channels and stops the scanning operation at a tuning point.

Among these, the scanning type selects a tuner by increasing or decreasing the tuning voltage input to the tuning terminal of the tuner at a constant speed.

In this method, a synchronizing signal extracted from an IF (intermediate frequency) is input to an integrating circuit, and the integrated value output from this integrating circuit is kept almost constant as a voltage value by the action of an AGC (automatic gain control circuit). is connected to one input terminal of a comparison circuit (comparator) through an inverting circuit that inverts the voltage at the boundary, and the voltage at the one input terminal is compared with a preset reference voltage in this voltage comparator, and the reference voltage is set as the reference voltage. It is configured to stop the scanning operation when the size becomes larger.

By the way, some of these scanning systems have means for switching between a mode in which only stations with a strong electric field are received and a mode in which reception is possible even in a weak electric field. This is achieved by varying the reference voltage input to the comparison circuit in multiple stages without changing the scanning speed; in other words, by raising and lowering the threshold level in the voltage comparator and changing the sensitivity of the tuner. be done.

Problems to be Solved by the Invention However, the above-described scanning type automatic channel selection device has the following problems. This will be explained below with reference to FIG.

Figure 4 is a timing chart showing the timing of each operation. In the figure, the horizontal axis represents time, and the graph (1
) indicates the voltage value on the vertical axis, and T5 indicates the timing to stop scanning in a mode that only receives stations with a strong electric field (hereinafter referred to as strong electric field mode), and T6 indicates the timing to stop scanning even when stations with a weak electric field are received. It shows the timing to stop scanning in the receiving mode (referred to as weak electric field mode), and T7 and T8 indicate the ON time of the push button etc. operated to start scanning in strong electric field mode and weak electric field mode, respectively. It is a diagram showing timing.

First, when a scanning operation is started in the strong electric field mode, the scanning operation is stopped at a point P2 of a certain strong electric field channel (channel 1 CHI in this example).

When the user wants to receive another channel, he operates a button or the like for starting scanning at the timing shown at T7. Then, the scanning operation is executed again and continues until the next tuning point.

By the way, in the weak electric field mode, the threshold level in the comparator circuit is lowered, so the receiving sensitivity is improved. However, the scanning operation stops at the same time. If the user's purpose is to receive the signal at point P2 of channel 1, he or she operates the button, etc., but the scanning time from the position of rebound portion P1 to the normal position P2 of channel 1 is very short. 4, the ON time t of the button, etc. is
1 may easily exceed the above-mentioned scanning time, and in that case, the scanning operation does not stop at the P2 position, but stops at the 23-point bounce position, resulting in a channel selection error. To avoid this, a button or the like must be operated instantaneously, making it inconvenient to use. Furthermore, one possible solution to this drawback is to slow down the scanning speed, but this has the drawback that slowing down the scanning speed (which in turn significantly increases the channel selection time in the strong electric field mode).

Means for Solving the Problems In order to solve the above problems, the automatic tuning device of the present invention has a sensitivity changeover switch that changes the reception sensitivity and a scanning speed change switch that changes the scanning speed in conjunction with each other, so that the automatic tuning device can operate in the strong electric field mode. In the weak electric field mode, the scanning speed is increased, and in the weak electric field mode, the scanning speed is decreased.

Operation With the above configuration, the automatic channel selection device of the present invention increases the scanning speed to shorten the channel selection time in the strong electric field mode, and slows down the scanning speed to select the channel in the weak electric field mode. It is possible to prevent station errors.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to FIGS. 1 to 3.

FIG. 1 is a block diagram showing the configuration of one embodiment. In the figure, 1 is a receiving sensitivity switching circuit, and a sensitivity switching switch 2 is connected to this receiving sensitivity switching circuit. Reference numeral 3 denotes a tuning control circuit that uses a signal from the sensitivity switching circuit to raise or lower the tuning voltage according to the speed set in the scanning speed changing circuit 4. In this tuning control circuit, the signal from the sensitivity switching circuit and A
Based on the FC (automatic frequency control) waveform, it is determined whether the tuning voltage should be raised or lowered or kept constant. The output from the scanning speed changing circuit is input to the tuning terminal of the tuner. Further, the scanning speed change switch 5 of the scanning speed change circuit 4 is configured to operate in conjunction with the sensitivity changeover switch 2.

Next, a specific example of the circuit block diagram shown in FIG. 1 is shown in FIG.

In FIG. 2, numeral 11 is a synchronization separation circuit which extracts a synchronization signal from the F-fold signal. 12 is an integrating circuit that inputs the synchronization signal output from the synchronization separation circuit 11, and 13 is an AGC (
14 is a reference voltage generation circuit; 15 is a voltage generated from the reference voltage generation circuit 14 and the inversion circuit; A comparison circuit (comparator) that compares the voltages output from the inversion circuit 13 and outputs a signal to the Schmitt circuit 16 when the voltage from the inversion circuit 13 is lower than the reference voltage; 17 is a tuning control circuit; circuit 1
The signal output from 7 is connected to a tuning terminal (BT terminal) of the tuner via a time constant circuit 18.

Further, a sensitivity changeover switch 19 is connected to the reference voltage generation circuit 14 for changing the threshold level of the comparator 16. This sensitivity changeover switch is a three-terminal switch, and can be switched between a first state in which terminal i and terminal 11 are short-circuited and a second state in which terminal ii and terminal stone are short-circuited. When the sensitivity changeover switch is in the first state, the resistance R
1 and R2 are connected in parallel, and the reference voltage input to one terminal of the comparator 16 is lower than the reference voltage when the sensitivity changeover switch is in the second state. That is, the first state is the strong electric field mode, and the second state is the weak electric field mode.

20 is a scanning speed changeover switch;
It is a 3 terminal switch. This switch 20 is connected to the terminal i when the sensitivity changeover switch 19 is in the first state.
V and the terminal V are short-circuited, and when the sensitivity change-over switch 19 is in the second state, the terminal V and the terminal vi are short-circuited in conjunction with the switching operation of the sensitivity change-over switch. When the scanning speed changeover switch is in the first state, that is, when terminals iv and V are shorted, the two resistors R3 and R4 in the time constant circuit 18 are connected in parallel, and the time constant becomes small. , so the scanning speed becomes faster. Furthermore, in the second state, the resistor R4 is disconnected, the time constant becomes large, and the scanning speed becomes slow.

Further, this will be explained in detail using FIG.

FIG. 3 is a timing chart showing the timing of the operation, similar to FIG. 4 used in explaining the conventional example. In FIG. 3, when the sensitivity changeover switch and the scanning speed changeover switch are in the first state, that is, in the strong electric field mode, the threshold level by the comparator 16 is set high (for example, level A in FIG. 3(a)). Therefore, the scanning operation stop timing is T1 in the same figure.
As shown. First, the scanning operation is stopped at position P2. When the user wants to select the next station, the user must press the button to start scanning at T2.
Operate at the timing shown below.

Next, when the sensitivity changeover switch and the scanning speed changeover switch are in the second state, that is, in the weak electric field mode, the threshold level by the comparator 16 is lower than in the first state (for example, as shown in FIG. 3). b) Medium B level), so the scanning operation stop timing is as shown in T3 in the figure. First, the scanning operation is stopped at the P1 position. However, this P1 position is Since this is a bounced part of the channel, the image displayed on the CRT will be degraded. Therefore, the user operates the button etc. at the timing shown in T4 to start scanning again. The operation time of
Even if the operation time t1 is the same as T2 in Figure (a), since the scanning speed is set slow by the time constant circuit 18, P
There will be no need to pass through two points. Therefore, mistakes in channel selection in the weak electric field mode are avoided.

Effects of the Invention As has become clear from the above explanation, the automatic tuning device of the present invention does not delay the tuning time in the strong electric field mode, and prevents mistakes in tuning in the weak electric field mode. It is extremely easy to use.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an automatic channel selection device according to an embodiment of the present invention, FIG. 2 is a more specific block diagram of the one shown in FIG. 1, and FIG. FIG. 4 is a timing chart showing the timing of each operation in a conventional automatic channel selection device. 1... Receiving sensitivity switching circuit 2... Sensitivity switching switch 3... Tuning control circuit 4... Scanning speed changing circuit 5...
...Scanning speed change switch 11...
... Synchronization separation circuit 12 ... Integration circuit 13 ... Inversion circuit 14 ... Reference voltage generation circuit 15 ... Comparison circuit 16 - Old Schmitt circuit 17...Tune selection control circuit 18...Time constant circuit Name of agent Patent attorney Toshio Nakao 1 person No. 31 (
a) 4th g

Claims (1)

[Claims] (1) A receiving sensitivity switching circuit that switches receiving sensitivity;
This automatic channel selection device is configured so that the scanning speed is linked with a scanning speed changing circuit that changes the scanning speed, and the scanning speed is slower when the reception sensitivity is high than when the reception sensitivity is low.