JPS59141806A - Amplifier circuit - Google Patents

Abstract

PURPOSE:To prevent the variation of frequency characteristics which is due to the temperature characteristics of an operational amplifier, by using a parts having temperature characteristics among the component parts of a feedback circuit. CONSTITUTION:An amplifier circuit is constituted by feeding negatively the output of an operational amplifier 1 back to the input of the amplifier 1 by a feedback circuit 2. The circuit 2 consists of a thermistor 3, etc. having temperature characteristics, a capacitor 4 and a coil, etc. having frequency characteristics. Thus the dependency on temperature is given to the frequency characteristics of the circuit 2. Then the feedback whose frequency characteristics are changed by temperatures is applied to the amplifier 1 via resistances 5 and 6. The temperature characteristics of the amplifier 1 can be compensated by setting properly the characteristics of the thermistor 3 as well as the value of the capacitor 4.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an amplifier circuit using an operational amplifier, and more particularly to an improvement in an amplifier circuit that prevents changes in frequency characteristics caused by temperature characteristics of the operational amplifier.

Amplification circuits consisting of an operational amplifier and a feedback circuit placed outside the operational amplifier have been widely used in many fields because the feedback circuit can set the gain, frequency characteristics, etc. of the amplifier circuit. This type of amplifier circuit is constructed by negatively feeding the output of an operational amplifier 1 to the input of the operational amplifier 1 through a feedback circuit 2, as shown in FIG. The feedback circuit 2 is a component Zl consisting of one or a combination of passive components such as a resistor, a capacitor, and a coil.

Consists of z2. The operational amplifier 1 is generally constructed using semiconductor components such as transistors, and the temperature dependence of the amplifier circuit can be ignored if the feedback circuit 2 is set to be sufficiently small in comparison. For example, when used in the first stage of a receiving system that requires high sensitivity, such as the first stage of an optical receiver, the difference between the two gains mentioned above is small, and the characteristics of the amplifier circuit change due to temperature changes. In particular, changes in frequency characteristics in high frequency bands are significant and cannot be ignored. Therefore, in the past, it has been usual to set the feedback circuit 2 so that the sensitivity of the receiver is sacrificed to some extent.

The object of the invention is to compensate for the temperature characteristics of an operational amplifier by using components having temperature characteristics among the components of the feedback circuit;
An object of the present invention is to provide an amplifier circuit that eliminates the drawbacks of the prior art.

According to the present invention, in an amplifier circuit composed of an operational amplifier and a feedback circuit disposed outside the operational amplifier, the feedback circuit includes components having temperature characteristics such as a thermistor, and components having frequency characteristics such as a capacitor and a coil. By using the above method, an amplifier circuit is obtained, which is characterized in that temperature changes in frequency characteristics are compensated for.

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

FIG. 2 shows a block diagram of an embodiment of an amplifier circuit according to the invention. The feedback circuit 2 of the operational amplifier 1 is made up of a thermistor 3 and a capacitor 4, so that the frequency characteristics of the feedback circuit have temperature dependence.

This change in characteristics due to temperature dependence is fed back to the operational amplifier 1 via resistors 5 and 6 so that the frequency characteristics change depending on temperature. By appropriately setting the characteristics of the thermistor 3 and the value of the capacitor 4, the temperature characteristics of the operational amplifier 1 can be compensated, and the object of the invention can be achieved.

FIG. 3 shows a configuration diagram of an embodiment in which the amplifier circuit according to the invention is applied to the first stage section of the original receiver of an optical communication system. In the optical receiver, the feedback resistance value of the feedback circuit 2, that is, the thermistor 7
, Contin v8. The greater the difference between the combined impedance of the circuit constituted by the resistor 9 and the resistance value of the variable resistor 11, the more the reception sensitivity tends to be improved. The input optical signal P is converted into a current signal by the photodetector 12 and amplified to become an output signal e. A portion of the output signal e is fed back to the input of the operational amplifier 1 by the feedback circuit 2. In the feedback circuit 2, the combined impedance of the circuit consisting of the thermistor 7, capacitor 8, and resistor 9 has temperature dependence. A feedback circuit with dependence can be realized.

Here, the variable resistor 11 is provided to finely adjust the frequency characteristics to be compensated.

FIG. 4 is a diagram showing the effect of the embodiment of FIG. 3 according to the invention, and FIG. 4(a) shows the case of a conventional amplifier circuit. There is a tendency for the frequency characteristics to rise in the high frequency range. In order to correct this, the frequency characteristics of the feedback circuit have temperature characteristics. In other words, by utilizing the fact that the resistance value of thermitas decreases as the temperature rises, the feedback circuit is synthesized on the high temperature side. The impedance is adjusted so that it decreases in the high frequency range. FIG. 4(b) shows an amplifier circuit using this feedback circuit. It can be seen from this figure that compensation for frequency characteristic changes due to temperature changes is achieved as intended by the invention.

As described above, according to the present invention, it is possible to provide an amplifier circuit in which the temperature dependence of frequency characteristics is compensated for in an amplifier circuit using an operational amplifier whose characteristics change depending on temperature.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram of a conventional amplifier circuit, Figure 2 is a configuration diagram of an embodiment of an amplifier circuit according to the invention, and Figure 3 is a diagram showing the configuration of an amplifier circuit according to the invention at the first stage of a receiver in an optical communication system. FIG. 4 is a block diagram of the applied embodiment, and is a diagram showing the effect of the non-inventive embodiment of FIG. 3. 1...Operation amplifier, 2...Feedback circuit, 3,7
......-Thermistor, 4,8.10...Capacitor, 5゜6.9...Resistor, 11...Variable resistor, 12...Photodetector, Zl...passive circuit, Z2...passive circuit. No.! Kouriki 2 Sen 3rd country

Claims (1)

[Claims] In an amplifier circuit consisting of an operational amplifier and a feedback circuit placed outside of the operational amplifier, components with temperature characteristics such as a thermistor and components with frequency characteristics such as a capacitor and coil are used in the feedback circuit to improve the frequency characteristics. An amplifier circuit characterized by compensating for temperature changes.