JPH0136361Y2 - - Google Patents

Description

[Detailed explanation of the idea]

The present invention relates to an automatic tuning device for a tuner, and when an intermediate frequency is used for auto-stop during automatic sweep tuning in a tuner using a synthesizer method, tuning can be performed with a simple circuit configuration by changing the bias voltage of a diode. An object of the present invention is to provide an automatic tuning device for a tuner that can perform the following operations. FIG. 1 shows a block system diagram of an example of a synthesizer-based tuner. In the figure, by operating the auto search tuning switch 1, a signal is input to the terminal 2a, and the local oscillation frequency generated by the synthesizer control IC 2 automatically starts to gradually change, resulting in an automatic sweep operation. is started. The local oscillation frequency taken out from the output terminal 2e of the synthesizer control IC 2 is applied to a mixing circuit (not shown) from the input terminal 7C of the tuner IC 7, and is supplied via the input terminals 6 and 7d, respectively.
Mixed with the signal (frequency conversion). Also, at the same time as the above automatic sweep operation starts, output terminal 2b of IC2
A muting signal is transmitted from the tuner IC 7, and this operates a muting circuit that mutates the output audio signal of the detection circuit (not shown) at the time of output from the output terminal 7e and the output terminal 9 of the tuner IC 7. Input terminal 3
The signal is supplied to the auto-stop control circuit 4 via line b. The intermediate frequency control circuit 3 has an auto-stop control circuit 4 and a switch circuit 5.
The configuration was as shown in the figure. In the figure, the same components as in FIG. 1 are designated by the same reference numerals. The auto-stop control circuit 4 is an NPN transistor Q.
The switch circuit 5 corresponds to the transistor Q. Since the tuner is out of tune when the automatic sweep starts, the output of the inverting circuit 8 made up of a comparator is at a high level, and the input terminal 3b
Since a high level muting signal is input to the transistor Q, the transistor Q is base biased at a high level and is in a saturated state. Therefore, noise etc. extracted from the output terminal 7b of the tuner IC 7 via the input terminal 3d on the base side of the transistor Q is not led to the output terminal 3e on the collector side of the transistor Q, and the output terminal 3e is kept at a constant voltage. When the above automatic sweep continues and the tuning frequency comes close to the broadcast signal frequency, the signal indicator DC voltage is output to the output terminal 7a of the tuner IC 7, and as the tuning frequency approaches the broadcast signal frequency, this DC voltage When the voltage exceeds a certain value, a low level (eg, OV) DC voltage is supplied from the inverting circuit 8, which performs a comparator operation, to the auto-stop control circuit 4 via the terminal 3a. This results in
Transistor Q shown in FIG. 2 is optimally base biased by a high level muting signal from input terminal 3b. On the other hand, at this time, an intermediate frequency signal is taken out from the output terminal 7b of the tuner IC 7 to the input terminal 3d, so this intermediate frequency signal is transmitted to the second terminal where the base bias voltage is in the optimum state.
It is supplied to the base of the transistor Q shown in the figure, and is further output from its collector to the output terminal _3e via the capacitor C1 (i.e., at this time, the first
The switch circuit 5 shown in the figure is in a closed state). The intermediate frequency signal taken out to the output terminal 3e is supplied to the input terminal 2d of the synthesizer control IC 2, and this stops the change in the local oscillation frequency, thereby stopping the automatic sweep operation and tuning the broadcast signal. Be in a synchronized state. Further, by supplying the intermediate frequency signal to the terminal 2d, the muting signal at the output terminal 2b becomes low level, and a muting cancellation signal is supplied from the output terminal 2c to the input terminal 3c of the intermediate frequency signal control circuit 3. As a result, muting is canceled and the output audio signal from the detection circuit (not shown) is output from a speaker or the like. Also, at this time, the terminals 3a and 3b shown in FIG.
Since both input signals are at low level, the base bias voltage of transistor Q becomes extremely small, and no base input intermediate frequency signal is output from the collector of transistor Q (switch circuit 5 is in an open state). In this way, it is possible to automatically tune in to the broadcast signal. However, as shown in FIG. 2, the intermediate frequency signal control circuit 3 described above uses the transistor Q as the switch circuit 5, so it is expensive, and the circuits around the transistor Q require many circuit parts, which takes up a lot of space. There were some shortcomings, such as taking off. The present invention eliminates the above-mentioned drawbacks, and one embodiment thereof will be described below with reference to FIG. 3.
FIG. 3 shows a circuit diagram of an embodiment of the device of the present invention.
In the figure, the same components as in FIG. 1 are denoted by the same reference numerals, and their explanations will be omitted. In FIG. 3, a diode D corresponds to the switch circuit ₅ shown in FIG.
Connected to the power supply voltage input terminal via _R2 .
Further, the cathode of the diode D is connected to the output terminal _3e via the capacitor C3. Furthermore, the anode of the diode D is connected to the muting signal input terminal 3b via a resistor _R3 , and to the intermediate frequency signal input terminal 3d via a capacitor _C2 . Next, to explain the operation of the device with the above circuit configuration, there are nine stages of operation from operating the auto search/tuning switch 1 shown in Fig. 1 to stopping the transmission of the intermediate frequency signal after tuning to the selected station. Accordingly, the input DC voltages at the input terminals 3a and 3b change as shown in the following table, so the diode D is turned on or off as shown in the following table.

[Table] In the above table, operation (1) is the operation when the auto search tuning switch 1 is operated, and operation (2) is the high level H level from the output terminal 2b of the synthesizer control IC 2 shown in Figure 1. The operation at the time when the muting signal is output,
In both cases, the voltage at the terminal 3b is low level L, and the voltage at the terminal 3a is high level H. In addition, in the table, operation (3) is the operation at the time when the muting signal is input to terminal 3b, operation (4) is the operation when the tuning frequency becomes near the frequency where the broadcast signal is present by automatic sweep, and operation (5)
means the operation at the time when the DC voltage for the signal indicator is output from the terminal 7a of the tuner IC 7, and in these series of operations (3) to (5), both the input voltages at the terminals 3a and 3b are Both are at a high level H. In the above operations (1) to (5), diode D is always reverse biased and turned off. Next, we reach operation (6) in the table above, which occurs when the signal indicator DC voltage exceeds a certain value and a low level L voltage is applied from the inverting circuit 8 to the terminal 3a. At this time, the high-level muting signal is still applied to the terminal 3b. Therefore, this behavior (6)
, the diode D is forward biased and turned on for the first time, so that the intermediate frequency signal input to the input terminal 3d passes through the capacitor C ₂ , the diode D, and the capacitor C ₃ to the output terminal 3e.
Output to. In this state, the intermediate frequency signal is input to the input terminal 2 of the synthesizer control IC2.
The automatic sweep operation continues via operation (7) applied to d until operation (8) in which the automatic sweep operation is stopped and an automatic tuning tuning state is entered. In the subsequent operation (9) in which the muting signal is canceled and the audio signal of the tuned broadcast can be heard, the muting signal is no longer supplied to terminal 3b, so both terminals 3a and 3b become low level, but the diode Since the cathode of D is connected to the positive power supply voltage input terminal via the resistor R ₂ , it is reverse biased and turned off, so that the transmission of the intermediate frequency signal to the output terminal 3e is stopped. Effects As described above, according to the present invention, by controlling the bias voltage to the diode, the intermediate frequency signal can be outputted through the diode as a signal that determines the timing to stop the automatic sweep operation, and therefore the transistor Compared to conventional equipment that uses diodes, diodes are cheaper, and the surrounding circuitry requires fewer circuit parts, making it cheaper to configure and requiring less space. It has the advantage of being easy to use.

[Brief explanation of the drawing]

FIG. 1 is a block system diagram showing an example of a synthesizer type tuner, FIG. 2 is a circuit diagram showing an example of a conventional device, and FIG. 3 is a circuit diagram showing an embodiment of the device of the present invention. 2...Synthesizer control IC, 2b
... Muting signal output terminal, 2d, 3d...
...Intermediate frequency signal input terminal, 2e...Local oscillation frequency output terminal, 3...Intermediate frequency signal control circuit, 3a
...DC voltage input terminal, 3b ... Muting signal input terminal, 3e, 7b ... Intermediate frequency signal output terminal, 4 ... Auto stop control circuit, 5 ... Switch circuit, 7 ... Tuner IC, 7a ... Signal indicator 8...Inverting circuit, Q...NPN transistor, D...Switching diode.

Claims (1)

[Scope of utility model registration request] When the DC voltage for the signal indicator of the tuner exceeds a certain value and the muting signal is being supplied, an intermediate frequency signal is extracted through the switch circuit, and the automatic sweep operation is stopped by outputting the intermediate frequency signal. In an automatic tuning device for obtaining a selective tuning signal output of a desired broadcast signal, the DC voltage input terminal is connected to a first terminal of a diode, the muting signal is connected to a second terminal of the diode, and the DC voltage input terminal is connected to a second terminal of the diode. When the voltage is above the certain value and the muting signal is input, the diode is biased in the forward direction, an intermediate frequency signal is extracted through the forward biased diode, and the intermediate frequency signal output from the diode is used to automatically transmit the signal. An automatic tuner selection device configured to stop the sweep operation.