JPS5933908A - Signal interrupting circuit - Google Patents

Abstract

PURPOSE:To attain the sufficient suppression up to a high frequency signal, by operating a switching element so as to attenuate an output signal to an amplifier means and making successively plural amplifier elements of the amplifier means into non-operating state. CONSTITUTION:A switching circuit 4 consists of resistors (R)1, R2 and a transistor (TR)1, an amplifier circuit 5 comprises R3-R10, a capacitor (C)2 and the TRs 2, 3 and an output stage circuit 7 is made up of R11, R12, C3, C4, TR4 and TR5. A voltage almost equal to ground potential is given from a synchronism detecting circuit 3 to the circuit 4 under a normal state and the TR1 is brought into non-operating state. Thus, a signal transmitted from a phase synchronism oscillating circuit 2 is amplified at the TRs 2, 3 and outputted via the circuit 7. A negative base potential is given from the circuit 3 to the TR1 under the state of out of synchronism and the TR1 is brought into the operating state. Then, the signal of the circuit 2 is absorbed in the TR1 and the TRs2- 5 are brought into nonconductive state and cut off at the same time.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a signal cutoff circuit that lowers the input signal and cuts off the output signal when an abnormality is detected in the input signal.

Conventionally, a signal cutoff circuit has been used to cut off the output of a phase synchronized circuit or the like when an abnormality is detected.

FIG. 1 is a block diagram showing a conventional circuit, in which out-of-sync detection circuit 3 detects out-of-sync of phase-locked oscillator 2, generates an alarm signal, and relays this alarm signal to the emitter or collector. A transistor T connected to
1 to the base of the oscillator 2 to operate the relay, thereby opening the relay contact in the contact circuit 4 provided after the amplifier circuit 5, and the output signal from the oscillator 2 to the terminal 6.
This prevents the signal from being transmitted to subsequent circuits.

In this way, in the conventional circuit having the contact circuit 4 using the relay RL, the capacitance between the relay contacts affects the high frequency signal, and even though the relay contacts are open, the amplifier circuit 5 A part of the amplified output signal leaks to the output terminal 6, and the output signal cannot be suppressed sufficiently.

SUMMARY OF THE INVENTION An object of the present invention is to provide a signal cutoff circuit which eliminates the above-mentioned drawbacks.

The circuit of the present invention includes an amplifying means having a plurality of amplifying elements;
a switching means having a switching element;
By operating the switching element, the output signal to the amplifying means is attenuated, and a plurality of amplifying elements of the amplifying means are sequentially brought into a non-Mib operating state.

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

FIG. 2 is a block diagram showing an embodiment of the present invention, in which reference numeral 1 is an input terminal, numeral 2 is a phase synchronized oscillation circuit,
The same number 3 is an out-of-sync detection circuit, the same number 4 is a switching circuit, the same number 5 is an amplifier circuit, and the same number 6 is an output terminal.

In the figure, in the normal state, the output signal of the phase-locked oscillation circuit 2 is amplified by the amplifier circuit 5 via the switching circuit 4, and sent to the output terminal 6. An out-of-synchronization alarm signal is given from the out-of-sync detection circuit 3 to the switching circuit 4, which blocks the signal sent out from the phase-locked oscillation circuit 2, stops the amplification function of the amplifier circuit 5, and outputs the output signal to the output terminal 6. It is configured to completely block out

FIG. 3 is a block diagram showing in detail the switching circuit 4 and amplifier circuit 6 of FIG. 2, and the same reference numerals as in FIG. 2 indicate the same components. In the figure, a switching circuit 4 is composed of resistors R1 and R2 and a transistor TRI, an amplifier circuit 5 is composed of resistors R3 to RIO, a capacitor C2, and transistors T It 2 and TR3, and an output stage circuit 7 is composed of resistors R11 and R12, capacitors C3 and C4, and transistors '1°R4 and TR5, which constitute a fuselage circuit.

In the figure, in a normal state, a voltage approximately equal to the ground potential is applied from the desynchronization detection circuit 3 to the switching circuit 4, and the base potential of the transistor TRI is approximately a static potential with respect to its emitter potential, so the transistor T
R1 is inactive and the impedance of its collector is infinite. Therefore, the signal sent from the phase-locked oscillator circuit 2 is passed through the DC blocking capacitor C1 to the base of the transistor TR2, which is given a normal bias voltage divided by the resistors 3 and R4. After being amplified by TR2 and TMO3, it is subjected to ↓υlow 1 impedance conversion by an impedance conversion circuit 7 including transistors TR4 and TR5, and is output from an output terminal 6 through a capacitor C4.

- When the out-of-sync state is detected by the out-of-sync detection circuit 3, an appropriate negative potential is applied from the detection circuit 3 to the base of the transistor i'R1 of the switching circuit 4, and the The transistor is in an operating state in which the base potential is lower than the emitter potential.

As a result, the impedance of the collector of the transistor TRI becomes almost zero, and the output signal sent from the phase synchronized oscillation circuit 2 is absorbed by the transistor TR,1 after passing through the capacitor C1.

At the same time, since the impedance of the collector of transistor TRI becomes zero, the transistor 'ra
Since the base potential of the transistor T If,2 is approximately equal to the ground potential, the emitter potential of the transistor T If,2 is at the ground potential, the collector is at a negative applied voltage, and the transistor T R2 becomes inactive.

As a result, the DC 1 potential of the transistor 'I'R3 changes in the same way as the transistor '1' It2, and the emitter potential of the transistors TIt4, Tut, and 2 changes from approximately 1/2 of the negative potential to the ground potential. Change, transistor T
I(, 2 to 1゛几5 i, J: All become inactive, and the amplification function of the amplifier circuit 5 is completely stopped, so the signal sent from the phase synchronized oscillation circuit 2 is not applied to the output terminal 6. completely blocked.

Although the present embodiment has been described with the configuration of the amplifier circuit 5 and the impedance conversion circuit consisting of the bushing-pull circuit, the bushing-pull circuit may be removed if necessary.

As described above, in the present invention, in addition to the switching circuit using transistors, the function of the amplifier circuit in the subsequent stage is also stopped at the same time, so that it is possible to achieve sufficient suppression of even high-frequency signals, and furthermore, it does not use a relay circuit. This has the effect of simplifying the circuit and improving reliability.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional signal cutoff circuit, FIG. 2 is a Norlock diagram showing an embodiment of the present invention, and FIG. 3 is a detailed block diagram of FIG. 2. In the figure, 1... input terminal, 2...
Phase-locked oscillation circuit, total...out-of-synchronization detection circuit, 4
...Switching circuit, 5...Amplification circuit, 6...Output terminal, 7...Output stage circuit. dream 2 diagram

Claims (1)

[Claims] It includes an amplifying means having a plurality of amplifying elements, and a switching means having a switching element, and by operating the switching element, the output signal to the amplifying means is attenuated and the plurality of amplifying means of the amplifying means are attenuated. A signal cutoff circuit characterized by sequentially putting elements into a non-operating state.