JPS5929395Y2 - Search stop circuit of auto search tuner - Google Patents

Description

[Detailed Description of the Invention] The present invention provides a search stop cycle suitable for use in an auto search tuner that stops auto search when an S curve characteristic signal is detected from a receiver. Voice male t1's aa A- Automatically changes the local oscillation signal from the local oscillation circuit to perform an auto search for a broadcasting station, and stops the auto search when an S curve characteristic signal is detected from the receiver. An auto search tuner is known that receives a broadcasting station that has generated the S-curve characteristic signal.

In normal cases, the search stop circuit of the auto search tuner includes an amplifier circuit that amplifies the S-curve characteristic signal detected from the receiver, and a stop signal that generates a stop signal in response to the output signal of the amplifier circuit. The automatic search is configured to stop as long as the S-curve characteristic signal exists, regardless of the magnitude of the S-curve characteristic signal.

However, when such an auto-search circuit as described above is used in a high-end radio receiver, the search stops even in a weak electric field layer with a lot of noise, which is inconvenient for listeners who desire high-fidelity reception with a high-end radio receiver.

The present invention has been developed in view of the above points, and will be described below based on embodiments and with reference to the drawings.

In the figure, 1 is a first signal input terminal to which an S-curve characteristic signal from a radio receiver is applied, 2 is an amplifier circuit that amplifies the S-curve characteristic signal applied to the first signal input terminal 1, and 3 is a resistor. 4 and the capacitor 5.
6 is a stop signal generating circuit that generates a stop signal in accordance with the output signal of the amplifier circuit 2; 7 is a second negative feedback path to which a signal corresponding to the electric field strength of the station received by the radio receiver is applied. Signal input terminals, 8 to 12 are first to fifth drive transistors that conduct according to the level of the signal applied to the second signal input terminal 7; 13 to 17 are the first to fifth drive transistors 8 to 12; A light emitting diode 18 for displaying field strength is provided corresponding to the drive transistor and is driven by the corresponding drive transistor, the base of which is connected to the collector of the second drive transistor 9, and when the second drive transistor 9 is conductive. A first control transistor 19 conducts, the first control transistor 18
a second control i-transistor that conducts when conducts;
is connected to the negative feedback circuit 3 by its collector-emitter path.
The second control transistor 1 is connected to short-circuit the second control transistor 1.
a third control transistor that becomes non-conductive when 9 becomes conductive;
and 21 are control input terminals to which a control signal for switching from rHJ to rLJ is applied in accordance with the operation of an auto search switch (not shown).

Next, the operation will be explained.

When the auto search switch is not operated and a certain station is being received, a signal corresponding to the electric field strength of the certain station is applied to the second input terminal 7.

If the electric field strength of the certain station is level "3", the first to third drive transistors 8 to 10
exhibits a conductive state, and the first to third light emitting diodes 13 to 15 light up to indicate that the electric field strength is level "3".

Therefore, since the first control transistor 18 is connected to respond to the operation of the second drive transistor 9,
When the signal of level "3" is applied and the second drive transistor 9 becomes conductive, the first control transistor 18 also becomes conductive.

However, since the auto search switch is not operated, the rHJ signal is applied to the control input terminal 21, and the second control transistor 19 is already conductive, so the operation of the first control transistor 18 is controlled by the second control transistor. There is no side effect on transistor 19.

Since the second control transistor 19 is conductive, the third control transistor 20 is not conductive, and the amplifier circuit 2 operates as an amplifier having a predetermined negative feedback path 3 and a gain rAJ.

Therefore, the signal applied to the first signal input terminal 1 is amplified by A times and applied to the stop signal generation circuit 6.

Thus, when auto-search is not being performed, the stop signal generating circuit 6 operates as a fine-tuning signal generating circuit and supplies a fine-tuning signal to the auto-search tuner.

Now, if the auto search switch is operated to enter the auto search state, the control signal applied to the control signal input terminal 21 changes from "H" to rLJ and has no effect on the second control transistor 19. I won't.

Therefore, the second control transistor 19 is controlled only by the output signal of the first control transistor 18.

When the auto search is started, the tuning frequency of the radio receiver changes, and while the tuning frequency is between stations, a signal corresponding to the field strength signal applied to the second signal input terminal 7 is transmitted. It is small.

Therefore, the first to fifth drive transistors 8 to 12 become non-conductive, and the first to fifth drive transistors 13 to 17 become non-conductive.
is extinguished, and the first and second control transistors 18 and 19
becomes non-conductive, and the third control transistor 20 becomes conductive.

Therefore, the negative feedback circuit 3 of the amplifier circuit 2 is short-circuited by the third control transistor 20, and operates as an amplifier with a gain of "1".

The amplifier with a gain of "1" cannot provide a sufficient input to the stop signal generating circuit 6, and therefore, no stop signal is generated while the third control transistor 20 is conductive.

Even if the auto search progresses and a weak electric field station is received, a stop signal will not be generated and the auto search will not stop).

In other words, the signal corresponding to the electric field strength of the weak electric field station is
Even when applied to the signal input terminal 7, since the level of the signal is low, the second drive transistor 9 remains non-conductive, so the first and second control transistors 18 and 19 also remain non-conductive. The third control transistor 20 also remains conductive.

Therefore, the amplifier circuit 2 also operates as an amplifier with a gain of "1", and no stop signal is generated.

When the auto search further progresses and a station with a sufficiently large electric field strength is received, a signal corresponding to the sufficiently large electric field strength is first applied to the second signal input terminal 7, and the level is set to, for example, "4". If so, the first to fourth drive transistors 8 to 11 are conductive, and the first to fourth light emitting diodes 13 to 16 are turned on.

Then, when the second drive transistor 9 becomes conductive, the first drive transistor 9 becomes conductive.
Then, the second control transistors 18 and 19 become conductive, and the third control transistor 20 becomes non-conductive.

Therefore, the amplifier circuit 2 comes to operate as an amplifier with a gain of "A".

The S-curve characteristic signal of the station having a sufficiently large electric field strength is applied to the first signal input terminal 1 in that state.

Therefore, a sufficiently large S-curve characteristic signal is applied to the input terminal of the stop signal generating circuit 6, and a stop signal is generated from the stop signal generating circuit 6 to stop the auto search.

When a station with an electric field strength equal to or higher than a predetermined level is received and the auto search is stopped, the control signal applied to the control signal input terminal 21 changes from rLJ to rHJ, and the second Control transistor 19 remains conductive, and third control transistor 20 remains non-conductive.

Therefore, the amplifier circuit 2 operates as an amplifier with a gain of rAJ, and can supply a sufficiently large input signal to the stop signal generation circuit 6, which operates as a fine adjustment signal generation circuit. On the other hand, a fine adjustment signal can be supplied.

The fine adjustment signal is used to perform AFC (automatic frequency control) to prevent the radio receiver from being out of tune.

Although not directly related to the present invention, if the state of the fine adjustment signal is detected and the local oscillation frequency is finely adjusted, the radio receiver can always maintain a correct tuned state.

According to the present invention, the electric field strength of the receiving station can be effectively displayed by the electric field strength display circuit formed by the drive transistor and the light emitting diode.

Since the amplifier circuit for amplifying the S-curve characteristic signal can be switched and adjusted according to the operation of the electric field strength display circuit, there is an advantage that the operation of the amplifier circuit can be adjusted accurately and easily according to the electric field strength.

In particular, the search stop circuit of the auto search tuner according to the present invention is configured to operate normally only when it receives a station with an electric field strength above a predetermined level. It can completely prevent stoppage and is highly effective when used in high-end radio receivers.

[Brief explanation of the drawing]

The figure is a circuit diagram showing an embodiment of the search stop circuit of the auto search tuner according to the present invention. Explanation of main drawing numbers, 2... Amplifier circuit, 6...
...stop signal generation circuit, 8-12...drive transistor, 13-17...light-emitting diode, 18,19°20...control transistor.

Claims (1)

[Claims for Utility Model Registration] Broadcasting stations are searched by automatically changing the oscillation frequency of a local oscillator, and when a station having an S-curve characteristic signal of a predetermined level or higher is received, the search is stopped and reception is performed. In an auto search tuner that performs a field strength display circuit including a plurality of light emitting elements for lighting up a desired one of the plurality of light emitting elements; An odo search tuner, characterized in that the amplification degree control circuit for controlling the amplification degree is removed, and the amplification degree of the amplification circuit is set to a predetermined value in response to lighting of a desired one of the light emitting elements. search stop circuit.