JPH02244806A - Signal amplifier circuit - Google Patents

Abstract

PURPOSE:To realize a fast response and to set an arbitrary limit voltage by providing a variable gain amplifier circuit, a transistor for gain control, and a constant voltage generating part. CONSTITUTION:A current flows on the base of the transistor 14 for gain control at a time when an amplified signal is increased than the voltage of the constant voltage generating part 15 by the Vbe of the transistor 14 for gain control, and continuity between the collector and the emitter is obtained, and the gain of the variable gain amplifier circuit 11 is lowered. Since no limit operation is started until the base current of the transistors 14 for gain control flows, the signal can be amplified to a preset limit voltage. Therefore, the gain itself of the variable amplifier circuit 11 is lowered by the transistor 14 for gain control when an invalid large signal is inputted. Thereby, no saturation occurs in output, and the fast response can be expected, and also, the limit current can be set at an arbitrary level.

Description

[Detailed Description of the Invention] [Summary] Regarding a signal amplification circuit used in a device that measures analog signals at high speed, the present invention aims to provide a signal amplification circuit that has a high speed response and can set an arbitrary limit voltage. A variable gain amplifier circuit, a gain control transistor whose emitter is input to the output of the variable gain amplifier circuit, and a voltage that is lower than the voltage to be limited by the base-emitter voltage of the transistor and applied to the base of the transistor. It consists of a constant voltage generator and a constant voltage generator.

[Industrial Application Field] The present invention relates to a signal amplification circuit used in a device that measures analog signals at high speed.

The analog signal is converted into a digital signal by an A/D converter and measured. In this case, if a very small analog signal is input to the A/D converter, a high gain amplifier circuit is used before the A/D converter.

Then, using a high gain amplification circuit using an operational amplifier,
When inputting the signal amplified by the high gain amplifier circuit to the A/D converter, a limiter is used so as not to exceed the rated input of the A/D converter.

In this case, the high gain amplifier circuit needs to respond at a sufficiently high speed in order to achieve sufficient performance of the A/D converter.

[Prior art and problems to be solved by the invention] A/
The conventional amplifier circuit used before the D converter is
For example, there are those shown in FIGS. 5 to 10, respectively.

In FIG. 5, 1 is an amplifier circuit consisting of an operational amplifier, 2
3 is an A/D converter that converts the analog signal amplified by the amplifier circuit 1 into a digital signal; 3 is a limiter made of a diode that limits the signal input to the amplifier circuit 1;
is the input signal source.

In this example, a limiter 3 is provided to prevent an unduly large signal from being input to the amplifier circuit 1.

However, in this example, the signals handled are minute, so
A simple limiter 3 made of a diode has a problem in that it is difficult to use because the set voltage is small.

Next, in the example shown in FIG. 6, the input signal source 4 and the limiter 3
Another amplifier circuit 5 consisting of an operational amplifier is provided between the two.

In this case, the set voltage can be increased, but there is a problem that when the limiter 3 is activated, the output of the amplifier circuit 5 in the previous stage is saturated, and a high-speed response cannot be expected.

Next, in the example shown in FIG. 7, a Zener diode 6 is used in the feedback circuit of the amplifier circuit 1.

In this case as well, since the Zener diode 6 usually has a large junction capacitance, there is a problem in that high-speed response cannot be expected.

Next, in the example shown in FIG. 8, a high-speed switching diode 7 is used in the feedback circuit of the amplifier circuit 1, and a high-speed limit operation is performed.

However, in this case, there was a problem that an arbitrary limit voltage could not be set.

Next, in the example shown in FIG. 9, a limiter 3 is provided between the amplifier circuit 1 and the A/D converter 2, and in the example shown in FIG. between 1
Two diodes 8 are provided, and a constant voltage generator 9 is connected to the diodes 8.

However, all of these examples have a problem in that when the input signal is large, the amplifier circuit 1 becomes saturated and high-speed response cannot be expected.

The present invention has been made in view of such conventional problems, and an object of the present invention is to provide a signal amplification circuit that has a high-speed response and can set an arbitrary limit voltage.

[Means for solving 11 problems] FIG. 1 is a basic configuration diagram of the present invention.

In FIG. 1, 11 is a variable gain amplifier circuit, 14 is a gain control transistor whose emitter receives the output of the variable gain amplifier circuit 11, and 15 is a voltage lower than the voltage to be limited by the base-emitter voltage of the transistor 14. This is a constant voltage generating section that generates a voltage and applies it to the base of the transistor 14.

[Function] The constant voltage generator 15 generates a voltage lower than the limit voltage by Vbe of the gain control transistor 14, and the constant voltage generated by the constant voltage generator 15 is input to the base of the gain control transistor 14. ing. Assume that an input signal is applied to the variable gain amplifier circuit 11. The amplified signal is applied to the emitter of gain control transistor 14.

When the amplified signal becomes larger than the voltage of the constant voltage generator 15 by Vbe of the gain control transistor 14, a current flows to the base of the gain control transistor 14.
The collector-emitter becomes conductive, reducing the gain of the variable gain amplifier circuit 11. Since the limit operation does not start until the base current of the gain control transistor 14 flows, the signal can be amplified up to the set limit voltage, and if an unreasonably large signal is detected, the gain control transistor 14 amplifies the gain itself of the variable gain amplifier circuit 11. Therefore, output saturation of the variable gain amplification circuit 11 does not occur and the amplification operation can be performed at high speed. Additionally, any limit voltage can be set.

[Example code] Embodiments of the present invention will be described based on the drawings.

FIG. 2 is a diagram showing an embodiment of the present invention.

First, to explain the configuration, in FIG. 2, 11 is a variable gain amplification circuit composed of an operational amplifier, and an AC voltage is supplied from an AC power supply 12 to its positive input terminal.

13 is an A/D converter;
converts the analog signal amplified by the variable gain amplifier circuit 11 into a digital signal.

14 is a gain control transistor that controls the gain of the variable gain amplifier circuit 11, and the signal amplified by the variable gain amplifier circuit 11 is input to the emitter of the transistor 14. The collector of the transistor 14 is connected to the variable gain amplifier circuit 1
Connected to the negative input terminal of 1.

15 is a constant voltage generating section, and the constant voltage generating section 15 includes a transistor 16, diodes 17, 18, and resistors 19.
20. The constant voltage generator 15 generates a voltage lower than the voltage to be limited by the base-emitter voltage Vbe of the transistor 14, and the constant voltage generated by the constant voltage generator 15 is applied to the base of the transistor 14. Note that 21 and 22 are resistors for gain setting.

Next, the operation will be explained.

A constant voltage generated by a constant voltage generator 15 is input to the base of the transistor 14 . Assume now that an input signal is applied to the variable gain amplifier circuit 11 from the input signal source 12. The signal amplified by the variable gain amplifier circuit 11 is input to the A/D converter 13 and is also applied to the emitter of the transistor 14 at the same time.

Here, when the amplified signal becomes larger than the constant voltage generated by the constant voltage generator 15 by the amount vbe of the transistor 14, a current flows to the base of the transistor 14, conduction occurs between the collector and emitter of the transistor 14, and the variable gain amplifier circuit 11 gain is lowered.

Normally, Vf of the diode 17 of the constant voltage generator 15 and Vbe of the transistor 14 are almost the same, and the limiter operation does not start until current flows to the base of the transistor 14. Therefore, the input of the A/D converter 13 is The signal can be amplified up to a set limit voltage without reducing the dynamic range. Further, an unreasonably large signal is detected by the variable gain amplifier circuit 11 by the transistor 14.
Since the gain itself is reduced, saturation of the output does not occur, and high-speed amplification operation can be performed.

Next, FIG. 3 is a diagram showing a second embodiment of the present invention.

This embodiment is an example in which a transistor is used instead of a diode in the constant voltage generating section.

In FIG. 3, 23 is the transistor 1 for gain control.
It is the same transistor as 4, and is used in place of the diode 17. Therefore, the constant voltage generating section 15 includes the transistor 16, the transistor 23, and the diode 188.
and resistors 19 and 20.

In this case, since the characteristics of the transistor 14 and the transistor 23 are the same, highly accurate limit operation can be expected. Note that the other configurations and effects are the same as those of the previous embodiment.

Next, FIG. 4 is a diagram showing a third embodiment of the present invention.

This embodiment is an example of an LSI.

In FIG. 4, the variable gain amplifier circuit 11, the gain control transistor 14, the resistors 21 and 22, and the constant voltage generating section 15 constitute an LSI 24 as a whole. When implemented as an LSI in this manner, the thermal coupling between the constant voltage generating section 15 and the gain control transistor 14 becomes perfect, so highly accurate limit operation can be expected. Note that the other configurations and effects are the same as those of the previous embodiment.

[Effects of the Invention] As explained above, according to the present invention, when an unreasonably large signal is input, the gain itself of the variable gain amplifier circuit is reduced by the gain control transistor, so that saturation of the output does not occur. High-speed response can be expected, and any limit voltage can be set.

[Brief explanation of drawings]

Fig. 1 is a basic configuration diagram of the present invention, Fig. 2 is a circuit diagram showing a first embodiment of the invention, Fig. 3 is a circuit diagram showing a second embodiment of the invention, and Fig. 4 is a circuit diagram showing a second embodiment of the invention. Third
A circuit diagram showing an embodiment, and FIGS. 5 to 10 are circuit diagrams showing a conventional example. In the figure, 11... Variable gain amplifier circuit, 12... AC power supply, 13... A/D converter, 14... Gain control transistor, 15... Constant voltage generator, 16.23. ...Transistor, 17.18...Diode, 19-22...Resistor, 24...LSI.

Claims (1)

[Claims] a variable gain amplifier circuit (11);
A gain control transistor (14) whose output is input to the emitter of 1) generates a voltage lower than the voltage to be limited by the base-emitter voltage of the transistor (14) and applies it to the base of the transistor (14). A signal amplifying circuit comprising: a constant voltage generating section (15).