JPS6160615B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electronic switch, and particularly to a switch circuit having a function of eliminating unnecessary input signals, which is extremely effective when applied to electronic channel selection of a television receiver.

FIG. 1 is an example of a conventional electronic switch circuit. That is, when an AC signal or a DC signal is applied from the input terminal a, the input amplifier 10 obtains a trigger signal with the amplitude necessary to change the state of the holding circuit (memory circuit). By adding to the trigger circuit 11 the holding circuit 12
trigger. This holding circuit 12 is a bistable circuit composed of transistors 4 and 5 and resistors 2, 3, 6, and 7.
1, a current flows through the transistors 4 and 6, and the potential at the output terminal c changes its output state to be close to the power supply potential. This state is maintained (stored) even after the trigger signal disappears. In the example of FIG. 1, the holding circuit 12 can be reset by temporarily turning off the power supply voltage and then turning it on again, but in practice, some kind of reset circuit is often added.

When such a circuit is used, for example, for electronic tuning of a television receiver, a plurality of the circuits shown in Fig. 1 are connected in parallel to both ends of the power supply, using resistor 3 as a common resistor (only one resistor 3 is used). , to a common emitter connection line to which the emitters of the respective transistors 1 and 4 are connected). In such a configuration, if the constant settings of the holding circuit, specifically the bistable circuit composed of transistors 4 and 5, are appropriate, only the holding circuit to which the input is applied can selectively change its state to that of other holding circuits. changes to a different state,
Retains that state even after the input is removed. Therefore, if the electronic tuner is controlled by the output, electronic tuning can be performed. Conventionally, in this type of configuration, an input signal of waveform A is applied to input terminal a, and a waveform of waveform C is generated at output terminal c. This changes the current flowing through the voltage setting circuit connected to output terminal c or through the ground line.
There is a problem in that it interferes with the voltage setting circuit and causes a noticeable striped pattern on the screen of the television receiver.

The present application provides an electronic switch circuit in which once the output state of the holding circuit is set, no input signal appears at the output even if an input signal is applied thereafter.

According to the present invention, the input terminal operates the first bistable circuit by the input signal, operates the second bistable circuit by the output thereof, and adds the input signal by the output of the second bistable circuit. Obtain a switch circuit to short-circuit.

Next, the present invention will be explained in more detail with reference to FIG.

The input amplifier 110 includes a Darlington circuit of transistors 121 and 122 connected to the input terminals, a transistor 125 whose base is connected to the connection point between its load resistors 123 and 124, and its load resistor 1.
26 and its output is applied to a trigger circuit 111 consisting of a transistor 127 to trigger the first holding circuit 112. Input amplifier 110
is included assuming that the input signal level is insufficient to trigger the first holding circuit.
This first holding circuit includes transistors 129 and 13.
1 and resistors 128, 130, and 132 form a bistable circuit such as a Schmitt trigger. The second holding circuit 113 includes a second trigger circuit so as to respond to the operation of a second trigger circuit 114 consisting of the first holding circuit 112, a transistor 137, and a bias source 138. 11
4 are connected. This second holding circuit 113
Also transistors 133, 136 and resistor 13
4,135 form a bistable circuit such as a Schmitt trigger. The output of the second holding circuit 113 is added to the input of the switch circuit 115 of the transistor 139, and after the output of each holding circuit 112, 113 is set by this switch circuit 115, the input signal is sent to the input amplifier. 110.

In such a configuration, if a rectangular wave as shown by A' in FIG. 2 is input to the input terminal a of the input amplifier 110, the transistor 12
The trigger circuit 111 is amplified by 1, 122, 125.
The transistor 127 forming the first holding circuit 112 drives the transistor 131 forming the first holding circuit 112 into a conductive state. In the initial state, the collector current of the transistor 131 immediately drives the transistor 129 because both the transistors 133 and 136 of the second holding circuit 113 are cut off, and makes the two transistors 129 of the first holding circuit 112 conductive. Since transistors 12 and 131 cause their respective base currents to flow through each other's collector currents, once they are triggered and conductive, the transistors 129 and 131 remain conductive even when the trigger signal is no longer present. In other words, it constitutes a bistable circuit.
Here, when the transistor 131 starts to conduct, the voltage at the output terminal c increases, and the second trigger circuit 1
14, the potential of the base bias 138 of the transistor 137 constituting the transistor 137 is exceeded.
When the base-emitter of the transistor becomes forward biased, the transistor 137 becomes conductive and the second holding circuit
The collector current of this transistor 136 drives the transistor 133 into a conductive state, and both transistors 136 and 133 become conductive. At this time, the voltage at the output terminal c is approximately between the resistor 132 and the resistor 13.
The voltage drops to a voltage dependent on the ratio of 4, and transistors 129, 131, 133, and 136 forming the first holding circuit 112 and the second holding circuit 113 all become conductive. When the second holding circuit 113 is triggered, its output simultaneously switches the switch circuit 115.
The transistor 139 constituting the amplifier 110 is rendered conductive to prevent input signals from being applied to the input amplifier 110.

In this way, when an input signal is applied to the input amplifier 110 from the input terminal a, the first holding circuit 111 operates, and when the state is held, the voltage at the output terminal c changes and the second trigger circuit 114, and the second holding circuit 113 is triggered. The second holding circuit 113 is triggered, operates and maintains its state, and at the same time operates the switch circuit 115,
Stops transmission of input signals. Therefore, from then on, the first and second holding circuits 112 and 113 maintain a constant operating state regardless of the presence or absence of the input signal at the input terminal, so that the output terminal c receives the signal shown in FIG. As shown in FIG. 2, when the first holding circuit 112 is triggered, the power supply potential appears temporarily, but thereafter no input signal component appears. Therefore, since the signal component synchronized with the input signal flowing to the ground line is generated only at the moment of triggering, it is possible to minimize interference with the output due to the input signal component occurring in the ground line.

Further, according to the present application, after the first holding circuit 112 maintains the operating state, the second holding circuit 113 is operated and its output quickly cuts off the input signal that becomes the trigger signal for the first holding circuit 112. Therefore, there is no malfunction caused by cutting off the input signal before the first holding circuit 112 maintains the operating state. Furthermore, the second holding circuit 113 is similar to the first holding circuit 11
2 holds the operating state, the second trigger circuit 1
14 is definitely triggered. Therefore, according to the present application, it is possible to construct an electronic switch circuit that operates stably with fewer malfunctions.

Incidentally, according to the embodiment of FIG. 2, the transistor 1
A single pulse with waveform RO' can be obtained from the output terminal b taken out from the collector of 25, and this pulse is converted into an appropriate waveform and used in the AFT of the television receiver.
This is extremely convenient for use as a default control signal.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an example of the prior art.
FIG. 2 is a circuit diagram showing an embodiment of the present application. In the figure, 1, 4, 5, 121, 122, 1
25, 127, 129, 131, 133, 13
6,137,139...transistor, 2,3,
6,7,123,124,126,128,13
0,132,134,135...Resistance, 138...
...Bias power supply, 10...Input amplifier.

Claims (1)

[Claims] 1 first and second transistors of different conductivity types, means for respectively coupling the base and collector of the second transistor to the collector and base of the first transistor, and an output signal from the base of the first transistor. a first bistable circuit having means for taking out the input signal, a means for amplifying and outputting an input signal, a third transistor having a base receiving the output of the means, and a collector-emitter conduction path of the third transistor. a second bistable circuit triggered by the output signal of the first bistable circuit;
an electronic switch circuit further comprising means for blocking a signal based on the input signal from being supplied to the third transistor in response to an output of the bistable circuit.