JPH04178006A - Amplifier circuit - Google Patents

Abstract

PURPOSE:To reduce fluctuation of a DC voltage at an output terminal by providing a dummy circuit operated when the amplifier circuit of multi-channel input/ single output is in operation. CONSTITUTION:A dummy circuit 9 is provided with a fixed level source 11, an input terminal 12 and an input circuit 10. When all input circuits 1 are not in operation, the added dummy circuit 9 is in an operating state and an output of the dummy circuit 9 is outputted to an output terminal 6. When any of the input circuits 1 is in operation, the dummy circuit 9 is inoperative by a changeover circuit 2' and an output of the input circuits 1 in the operating state is outputted to the output terminal 6. As a result, even when fluctuation of each input circuit itself is large, when the input circuits 1 are of the same circuit constitution, the input offset voltage is at an equal level and output fluctuation is much reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an amplifier circuit, and more particularly to an amplifier circuit that switches between operation and non-operation of a two-input circuit with a multi-channel input and a single output.

[Conventional technology]

In FIG. 3, the conventional amplifier circuit includes input terminals 5 to which n signal sources 8 are respectively input, n input circuits 1 to which each input terminal 5 is input, an input switching circuit 2, and an output. It includes a circuit 3, a switching circuit 4, a fixed potential 7, and an output end 6.

A conventional amplifier circuit of this type is composed of a plurality of input circuits 1, an input switching circuit 2, an output circuit 3, and a switching circuit 4. Here, when the input circuit 1 is operating, one of the plurality of input circuits 1 is selected and a signal is output from the output terminal 6. When the input circuit 1 does not operate, the output terminal 6 is switched to a fixed potential 7 so that the direct current voltage (hereinafter referred to as DCT) at the output terminal 6 does not fluctuate.

The operation of the amplifier circuit in FIG. 3 is shown in FIG. 4.
FIG. 6 is a timing diagram showing changes in voltage at the conventional output terminal 6;

In FIG. 3, when the output terminal 6 is switched from the fixed potential 7 to the output of the output circuit 3 by the switching circuit 2, that is,
When the input circuit 1 changes from a non-operating state to an operating state,
The DC voltage change at the output end 6 changes from the fixed potential 7 to the output of the input circuit 1. For this reason, D at output terminal 6
C voltage fluctuation is the voltage fluctuation of input circuit 1, that is, input port M
It is determined by the input offset voltage of l, and if the input offset voltage of the input circuit 1 is large, the voltage fluctuation at the output terminal 6 will also be large.

[Problem to be solved by the invention]

The conventional amplifier circuit described above has a circuit configuration in which when all of the input circuits 1 are not operating, the output terminal 6 is fixed and switched to 7 so that the output terminal DC voltage does not fluctuate. Therefore, if there is an input offset voltage at the input of input circuit 1, a difference will occur between the output terminal potential of fixed position 7 and input circuit 1, and the signal will be transmitted to the input of the fifth stage circuit as a glitch (whisker at the time of switching). However, there are disadvantages in that the response of the next stage becomes slow or it causes malfunction of the next stage.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned drawbacks and to provide an amplifier circuit in which glitches do not occur during switching.

[Means to solve the problem]

The configuration of the amplifier circuit of the present invention includes a plurality of first signal input circuits into which external signals are respectively input, a switching circuit for selectively outputting one of the outputs of these first signal input circuits, and In the amplifier circuit provided with an output circuit that receives the output of the switching circuit as an input, a second signal input circuit whose input is connected to a fixed potential and has a circuit similar to the first signal input circuit receives the first signal. It is characterized in that the signal is connected to be input to the output circuit during a non-operation period of the input circuit.

〔Example〕

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

FIG. 1 is a block diagram of an amplifier circuit according to an embodiment of the present invention, and FIG. 2 is a timing chart showing changes in DC voltage at the output terminal of FIG. In FIG. 1, in this embodiment, a second signal input circuit (dummy circuit) 9 surrounded by a broken line,
Switching port surrounded by dotted chain line! +2 has been added. Furthermore, the fixed potential 7. The switching circuit 4 has been removed. Other parts are the same as in FIG. 3.

The dummy circuit N9 in FIG. 1 is fixed; digit 11 and input terminal 12.
and an input circuit 10. In FIG. 1, when all the input circuits l are not operating, the added dummy circuit 9 is in the operating state, and the output of the added dummy circuit 9 is output to the 8 terminal 6. Multiple input ports N1
When any one of the input circuits 1 and 2 is in an active state, the added dummy circuit 9 is in a non-active state, so that the output of the input circuit 1 in an active state is outputted to the output terminal 6. As a result, no matter what state the input circuit 1 is in, the output terminal 6 is the input port! ? i
1. Or, since it is the output of dummy times n90 bodies, input circuit 1
The fluctuation for a single unit is at most 7. If each input circuit 1 has the same circuit configuration, the input offset voltages will be at the same level, so that output fluctuations can be considerably reduced.

〔Effect of the invention〕

As explained above, the present invention provides a dummy circuit that operates when all input circuits are not operating in a multi-channel input/single output amplifier circuit.
This has the effect of reducing fluctuations in the output terminal DC voltage.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an amplifier circuit according to an embodiment of the present invention, and FIG. 2 is a timing chart showing fluctuations in the DC voltage as the voltage at the output terminal of FIG. 1 changes. 1.10--input circuit, 2--input switching circuit, 3-
... Output circuit, 4... Switching circuit, 5, 12... Input terminal, 6... Output terminal, 7, 11... Fixed potential, 8...
...Signal order, 9...Second signal input circuit (dummy circuit).

Claims (1)

[Claims] A plurality of first signal input circuits to which external signals are respectively input are provided, a switching circuit is provided for selectively outputting one of the outputs of the first signal input circuits, and an output whose input is the output of the switching circuit. In the amplification circuit provided with the circuit, a second signal input circuit having an input connected to a fixed potential and having a circuit similar to the first signal input circuit operates as described above during the non-operation period of the first signal input circuit. An amplifier circuit characterized in that the amplifier circuit is connected to be inputted to an output circuit.