JPS59156008A - Signal input blocking circuit - Google Patents

Abstract

PURPOSE:To block simultaneously different kinds of signals by a single switch means by interrupting a common path of the signals. CONSTITUTION:An HI level is impressed normally to a control terminal 6, a transistor(TR) 5 is conductive deeply and a nearly ground level is given to a connecting point 9. An operational amplifier 3 is in the operating region amplifying an input signal in this state and further protection diodes D1, D2 for input clamp also the input signal. If a negative excess signal is impressed to an input terminal 1, the TR5 is back-biased. Then, when the input signal to an amplifier circuit 2 is desired to be blocked, an L0 level is impressed to the control terminal 6 to cut off the TR5 and the common path of the signal to the operational amplifier element 3 is cut off. Moreover, since a potential at a negative power supply terminal 8 of the operational amplifier element 3 follows nearly the potential of the signal path, the signal output to the output of the amplifier circuit 2 is blocked.

Description

[Detailed description of the invention] Technical field The present invention relates to a signal input blocking circuit applied to an amplifier or the like.

BACKGROUND OF THE INVENTION When configuring an electronic circuit network, there is often a need to configure it in such a way that signal input to a certain amplifier circuit is temporarily blocked. Let me give you a suitable example.

This is the read amplifier itself when connected to the read/write head of the cassette device. When a write direct current is applied to the head, an excessive signal is also added to the input of the amplifier. Therefore, it is necessary to prevent signal input to the read amplifier circuit, both from the read amplifier's own retention and from the standpoint of eliminating the inconvenience of outputting a pseudo read data signal during writing.

Conventionally, a highly reverse-biased diode circuit was connected in series with the input of the amplifier circuit.

There is also a device that blocks the write signal from being input to the read amplifier side during writing by controlling the bias. However, in order to implement this method, it is necessary to add extra elements and circuit networks, which also causes an increase in costs in order to construct an inexpensive device.

SUMMARY OF THE INVENTION The present invention has been devised in view of the disadvantages of the prior art, and it is therefore an object of the present invention to provide a signal input blocking circuit capable of blocking signal input to an amplifier circuit with a simple configuration.

EXAMPLE An example of the present invention will be described in detail below with reference to one drawing. FIG. 1 is a circuit diagram showing a signal input blocking circuit according to one embodiment. In the figure, l is a signal input terminal to the subsequent amplifier circuit 2, and DI and D2 are protection diodes for clamping excessive input.

C is a compling capacitor. The amplifier circuit 2 includes an operational amplifier element 3, and a resistor R1 that determines the degree of amplification.
, R2, and a Zener diode Z1. which clamps the upper and lower limits of the amplifier output. With Z2.

and a resistor R3 that protects the output circuit of the operational amplifier element 3. The amplifier circuit 2 may be an amplifier circuit with suitable sound, which is a combination of transistors and the like. Further, +Vcc is applied to the positive power supply terminal 7 of the operational amplifier element 3, and the negative power supply terminal 8 is a protection diode.

It is connected to the connection point 9 with DI and D2. Reference numeral 5 denotes a transistor serving as a switching means, the collector of which is connected to the node 9, and the emitter of which is grounded. In the embodiment, the ground circuit is the common path for the signals. Further, the base is connected to +Vcc by a pull-up resistor R4, and when the signal applied to the control terminal 6 is HI, the transistor 5 is made conductive to supply GND to the connection point 9, and when it is LO, it is connected to GND. cut off. The function of the transistor 5 may be replaced by an FET element, a C-MOS analog switch element, a relay contact, or the like.

6. Anode 4 is a demodulator that outputs the output of amplifier circuit 2 by 4 km. b The operation of this configuration will be explained below.

In the figure, a HI level is normally applied to the control terminal 6 (9). Therefore, transistor 5 becomes deeply conductive and connects to node 9.
tX gives the ground level. In this state, operational amplifier 3
is in the operating region that amplifies the input signal. The input protection diodes Dl and D2 also serve the purpose of clamping the input signal. If a negative excessive signal is applied to the input terminal l, the transistor 5 is reversed I (earthed). In such a case, Transistor 51C-MOS may be replaced with an a9log switch element.Next, if it is desired to block the input signal to amplifier circuit 2, LO level is applied to control terminal 6 to cut off transistor 5.

Common path tl of the signal to the operational amplifier element 3 - cutoff.

Thereafter, since the potential of the negative power supply terminal 8 of the operational amplifier element 3 approximately follows the potential of the signal path, the signal output to the output of the amplifier circuit 2 is blocked. At the same time, protection diode D1.
-02 also serves to protect the input circuit of the operational amplifier element 3 by limiting the charging of the coupling capacitor C.

In the embodiment, it is clear that the same effect can be obtained even if the emitter of transistor 5 is connected to a negative power supply. Further, the signal input blocking circuit according to the present invention is not limited to the polarity of the power supplied to the amplifier circuit 2 as in the embodiment.

Effects As described above, according to the present invention, it is possible to block signal input to the signal amplification means with a simple configuration. Conventionally, signal input is blocked by switch means inserted in series in the signal path, so if different types of signal paths exist, the number of switch means equal to the number of signal paths is required. However, according to the present invention, since the common path of signals is blocked, different types of signals can be blocked simultaneously by a single switch means. In devices that handle multi-channel signals, such as cassette devices and computer magnetic tape devices, it is also highly effective in reducing device costs.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an embodiment showing a path for blocking an input signal to an amplifier. Here, l...signal input terminal, 2... amplifier circuit, 3...
- Op-amp candy, 4... demodulator, 5... transistor. 6...Control terminal, 7...Positive power supply terminal, 8...Negative power supply terminal, 9...Connection point. Membership Application Δ Canon Co., Ltd.

Claims (1)

[Claims] 1. Amplifying means for amplifying a signal inputted via a signal path and a common path for the signals, and an amplifying means connected in series between the common path and the amplifying means; and switch means for controlling the opening and closing of the space. A signal input blocking circuit characterized in that signal input to the amplification means is blocked by controlling the switch means to open.