JP2593082Y2 - Gain correction amplifier circuit - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gain correction amplifier circuit, and more particularly, to a gain correction amplifier circuit using a thermistor.

[0002]

2. Description of the Related Art It is well known to perform temperature compensation using a thermistor whose resistance value changes with temperature. In particular, an NTC type thermistor having a negative temperature coefficient, that is, a resistance value decreasing as the temperature rises, Widely used for gain correction amplification circuits in electronic circuits. A typical prior art is shown in FIG. The circuit shown is a transistor Q1
1 is a common-emitter type amplifier circuit 11. The input signal Vin applied to the input terminal 12 is coupled to the coupling capacitor C
12, through the line L11 and the transistor Q11
Is entered at the base of The collector of the transistor Q11 is connected to the power supply voltage V of the power supply line L12 via the resistor Rc.
cc is supplied, the output line L13 is connected via the coupling capacitor C13, and the amplified output Vou is connected to the output terminal 13.
t is derived. The emitter of the transistor Q11 is grounded via a resistor R11, and is connected in parallel with the resistor R11 to NT.
A series circuit of a C-type thermistor Rt and a bypass capacitor C11 is connected. The gain correction utilizes the temperature characteristics of the thermistor Rt. If the capacitance of the bypass capacitor C11 is set to a sufficiently low impedance with respect to the frequency of the input signal Vin, the gain Ac of the common-emitter amplifier circuit 11 will be the same as that of the resistances of the resistors Rc, R11 and the thermistor Rt. In general, Ac = Rc / [re + (R11 // Rt)] (1) Here, re is the internal emitter resistance of the transistor Q11. The symbol “//” indicates a parallel combined resistance of the resistor R11 and the thermistor Rt. Since the gain of the common-emitter type amplifier circuit 1 decreases as the ambient temperature rises, it is possible to compensate for the gain change due to the change in the ambient temperature by operating this gain change to offset the change in the resistance value of the thermistor. it can.

[0003]

However, in the gain correction according to the prior art as described above, there is a problem that the gain changes during use due to insufficient consideration of the conduction characteristics. As is well known, the value of a component such as a resistor in a circuit changes due to Joule heat caused by a current flowing during operation. Therefore, when considering the gain correction of a circuit due to temperature changes, it is not complete without considering not only external factors such as changes in ambient temperature, but also internal factors such as changes in circuit constant values due to self-heating. . For example, in the common-emitter type amplifier circuit 11 shown in FIG. 3, the resistor R11 has a negative feedback function of automatically suppressing an increase in the collector current Ic of the transistor Q11 due to a rise in temperature. The meaning provided is then diminished. As shown in the above equation (1), the circuit gain Ac is affected by the resistance value. However, in the above-described common-emitter type amplifier circuit 11, the resistance value of the thermistor Rt is effective for an external factor such as a change in the ambient temperature, so that it is effective. Not valid for This is because, in the gain correction of the prior art, the thermistor Rt inserted in the circuit is cut off in direct current by the bypass capacitor C11, and therefore has only a function of a temperature sensor during use. Therefore, the resistors R11 and R
As a result, the temperature compensation by the thermistor Rt cannot be performed sufficiently because of the inability to follow the current-carrying characteristics such as c.

SUMMARY OF THE INVENTION An object of the present invention is to provide a gain correction amplifier circuit which solves the above-mentioned problems by a simple circuit change, and which takes into account not only the change in ambient temperature but also the conduction characteristics. It is to be.

[0005]

The present invention provides a first resistor Rc for determining the gain of an amplifier circuit, a second resistor R2 for determining the gain of the amplifier circuit together with the first resistor Rc, And a bypass capacitor C1 having a sufficiently low impedance, a first resistor Rc is connected to the collector of the transistor Q1, and a parallel circuit comprising the second resistor R2 and the bypass capacitor C1 is connected to the emitter of the transistor Q1. A gain correction amplifying circuit, characterized in that a temperature compensating thermistor Rt having a temperature coefficient of an opposite sign to the second resistor R2 is connected in series to the parallel circuit.

The present invention also provides a third resistor R1 which determines the gain of the amplifier circuit together with the first resistor Rc and the second resistor R2.
And the third resistor R1 is connected in parallel to the temperature compensation thermistor Rt.

[0007]

In the gain correction amplifier circuit according to the present invention, a temperature compensating thermistor connected in series to the second resistor R2 for determining the gain of the amplifier circuit is provided on the DC return path. As a result, a part of the emitter current of the transistor is shunted and self-heated to the thermistor, so that a desired temperature compensation characteristic can be obtained even if a resistance value change due to a current-carrying characteristic is applied in addition to a change in ambient temperature. Thus, the gain of the amplifier circuit can be effectively corrected.

According to the present invention, the third resistor R determines the gain of the amplifier circuit in parallel with the temperature compensating thermistor Rt.
1 is connected, so that the gain of the amplifier circuit can be more accurately corrected.

[0009]

FIG. 1 is a circuit diagram showing a configuration of a gain correction amplifier circuit according to an embodiment of the present invention. A resistor R is connected to the base of the transistor Q1 which constitutes the common-emitter type amplifier circuit 1.
3, a base bias voltage is applied by a voltage dividing circuit by R4. Input signal Vin applied to input terminal 2
Is input to the base of the transistor Q1 via the coupling capacitor C2 and the line L2. Transistor Q
1 is supplied with the power supply voltage Vcc of the power supply line L1 via the resistor Rc, the output line L3 is connected via the coupling capacitor C3, and the amplified output V
out is derived. One end of the gain correction amplifier circuit 4 according to the present invention is connected to the emitter of the transistor Q1, and the other end is grounded. The gain correction amplification circuit 4 includes a resistor R
1, R2, thermistor Rt, and bypass capacitor C1
And a series-parallel circuit.

As described above, the bypass capacitor C1 has a sufficiently low impedance with respect to the frequency of the input signal Vin.

In this embodiment, it should be noted that the connection point between the thermistor Rt and the bypass capacitor C1 and the resistance R
1 and R2 are connected by a line L4. As a result, the thermistor Rt is grounded via a part of the resistor inserted on the emitter side, and a DC return is formed. Therefore, thermistor Rt
A part of the emitter current of the transistor Q1 is shunted,
Like the resistors R1 and R2 arranged in parallel, during operation, the heater is self-heated by Joule heat caused by the supplied current. Resistance R1, R2
Have a positive temperature coefficient, whereas the thermistor Rt has the opposite sign to the temperature coefficients of the resistors R1 and R2. Since it has a negative temperature coefficient, the current-carrying characteristics during operation are canceled out, the change in the combined resistance value on the emitter side viewed from the transistor Q1 is suppressed, and the compensation function of the thermistor Rt against the ambient temperature is not impaired at all. It is. According to the present invention, the gain correction of the circuit can be improved in both the temperature change and the current-carrying characteristics by the simple configuration of slightly modifying the circuit on the emitter side of the transistor Q1.

FIG. 2 shows a gain correction amplifier circuit 4 according to the present invention.
FIG. 9 is a circuit diagram showing an example in which is applied to an intermediate frequency amplifier circuit of an FM receiver. The intermediate frequency amplifying circuit 21 has the same configuration as that of the common-emitter type amplifying circuit 1 shown in FIG. 1 described above, and the corresponding parts are denoted by the same reference numerals and description thereof will be omitted. In FIG. 2, an input signal IF applied to an input terminal IN is amplified by a preamplifier 5 and input to an input terminal 2 of an intermediate frequency amplification circuit 21 via a first band pass filter 6 realized by a ceramic filter or the like. And applied to the base of transistor Q1. Since the DC component is cut by the filter 6, the coupling capacitor C2 on the input side in FIG.
Are omitted together with the coupling capacitor C3 inserted on the output side. The output of the intermediate frequency amplifying circuit 21 is input to the next-stage detection circuit 8 via the output terminal 3, and a low-frequency signal LF is extracted by detection, amplified by the low-frequency amplifying circuit 9, and acoustically output from the speaker 10 or the like. You.

In such a circuit configuration, for example, even if the gain is reduced due to the current-carrying characteristics in the preamplifier circuit 5 and the detection circuit 8 in the subsequent stage, the current-carrying characteristics are corrected by the gain correction amplifier circuit 4, and therefore, Undesirable problems such as a decrease in circuit gain can be prevented. In the circuit configuration shown in FIG. 2, the amplification circuit including the gain correction amplification circuit 4 is inserted between the preamplification circuit 5 and the detection circuit 8, but the preamplification circuit 5, the detection circuit 8, The low frequency amplifying circuit 9 and the like may also be provided with the gain correction amplifying circuit 4, thereby performing gain correction over the entire device.

[0014]

As described above, in the gain correction amplifier circuit according to the present invention, the temperature compensation thermistor connected in series to the second resistor R2 for determining the gain of the amplifier circuit is provided on the DC return path. , A part of the emitter current of the transistor is shunted and self-heated, and in addition to a change in ambient temperature, a change in resistance due to current-carrying characteristics is added to obtain a desired temperature compensation characteristic and effectively correct the gain of the amplifier circuit. be able to. In addition, the present invention can improve the gain correction as described above by a simple method of changing the connection of the thermistor, so that the present invention can be easily and inexpensively applied to a conventional circuit.

Further, according to the present invention, since the third resistor R1 for determining the gain of the amplifier circuit is connected in parallel with the temperature compensating thermistor Rt, the gain of the amplifier circuit can be corrected more accurately. Become like

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of a gain correction amplifier circuit according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing an application example of the gain correction amplifier circuit shown in FIG. 1;

FIG. 3 is a circuit diagram showing a configuration of a gain correction amplifier circuit according to the prior art.

[Explanation of symbols]

 Reference Signs List 1 gain correction amplifier circuit 2 input terminal 3 output terminal L4 DC return of thermistor Q1 transistor R1, R2 resistor Rt thermistor C1 bypass capacitor Vin input signal Vout output signal

Claims (2)

(57) [Scope of request for utility model registration] 1. A first resistor Rc for determining a gain of an amplifier circuit
A second resistor R2 that determines the gain of the amplifier circuit together with the first resistor Rc, and a bypass capacitor C1 having a sufficiently low impedance with respect to the frequency of the input signal. The first resistor Rc is connected to the collector of the transistor Q1. In a common-emitter type amplifier circuit in which a parallel circuit including a second resistor R2 and a bypass capacitor C1 is connected to the emitter of the transistor Q1, a temperature compensating thermistor Rt having a temperature coefficient opposite to that of the second resistor R2 is provided. A gain correction amplifier circuit connected in series to the parallel circuit. 2. The semiconductor device according to claim 1, further comprising a third resistor R1 for determining a gain of the amplifier circuit together with the first resistor Rc and the second resistor R2, wherein the third resistor R1 is connected in parallel to the temperature compensating thermistor Rt. The gain correction amplifier circuit according to claim 1.