JPH0261172B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a broadband amplifier circuit using a current mirror circuit, which has a small temperature drift and is particularly suitable for ICs.
This invention relates to a wideband amplifier suitable for

[Background of the Invention] Current mirror circuits are stable because the current amplification factor is determined by the emitter area ratio of the transistor, and because the amplification section operates only with current, they can operate at extremely high speeds, so they are also used in wideband amplifiers. has been done.

Conventionally, as shown in US Pat. No. 3,531,730, for example, the method of inputting current to the current mirror circuit has been to connect the voltage signal input point and the current input point of the current mirror circuit with a resistor.

This conventional example is shown in FIG. In this diagram,
Reference numeral 1 designates a current mirror circuit, which includes a diode-connected transistor 10 with its base and collector connected, and n transistors 11 ₁ and 11 whose collectors, bases, and emitters are respectively commonly connected.
₂ ,...11n transistors 11,
The base and emitter of transistor 10 are connected to the base and emitter of transistor 11, respectively. n transistors 11 ₁ , 11 ₂ ,...11n forming the transistor 11 and the transistor 1
It is assumed that transistors 0 are of the same type, have the same emitter area, and have a sufficiently large current amplification factor.

A resistor 20 is connected between the collector of the transistor 10, which is the input of the current mirror circuit 1, and the input terminal 200.

The collector of transistor 11, which is the output of the current mirror circuit, is connected to output terminal 100.

The operation of the conventional example configured as above will be explained below.

First, when a voltage signal is applied to the input terminal 200, it is converted into a current signal by the resistor 20 and flows into the diode-connected transistor 10 of the current mirror circuit 1. This current is the input current I ₁ n of the current mirror circuit 1. Next, the output terminal 100
When a suitable bias voltage is applied to the transistor 11, a current equal to that of the transistor 10 flows through the n transistors forming the transistor 11. Therefore, the collector of the transistor 11 is connected to the transistor 10.
n times the current flows. In other words, the output current Iout of the current mirror circuit is n·I ₁ n.

Here, the input current Iin of current mirror circuit 1
is related to the input voltage v ₂₀₀ applied to the input terminal 200, the base-emitter voltage V _BE of the transistor 10, and the resistance value R ₂₀ of the resistor 20, and is expressed by the following equation.

Iin=V ₂₀₀ −V _BE /R ₂₀ (1) As shown in equation (1), the input current Iin of the current mirror circuit depends on the voltage V _BE between the base and emitter of the transistor. The base-emitter voltage V _BE typically has a value of about 0.7V, which is about -2mV/
It has a temperature coefficient of °C. Therefore, even if the input voltage V ₂₀₀ is constant, the input current Iin varies depending on the temperature.

This characteristic is shown in FIG. From this, the input voltage
It can be seen that the relationship between V ₂₀₀ and input current Iin drifts in the direction of increasing input current as temperature increases.

As described above, conventional broadband amplifiers using current mirror circuits have the problem of being affected by temperature.

This temperature effect can be solved by adding an emitter follower circuit to increase the impedance at the voltage input terminal.
If the current mirror circuit is changed to a base current correction type, it will become even larger. Furthermore, as can be seen from equation (1), if the amplitude of the input voltage Vin is small, the temperature influence value becomes relatively large, and there is a drawback that the power supply voltage cannot be lowered.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a broadband amplifier with temperature drift corrected.

[Summary of the invention]

The present invention corrects temperature drift by connecting to the input of the current mirror circuit a second voltage-current conversion circuit having almost the same temperature characteristics as the first voltage-current conversion circuit that inputs current to the current mirror circuit. It is characterized by:

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG. In FIG. 1, a current mirror circuit 1 and a resistor 20 have the same structure as the conventional example shown in FIG. The voltage-current conversion circuit 3 consists of a transistor 31 and a resistor 30, the resistor 30 is connected to the emitter of the transistor 31 and the ground point, and the base and collector of the transistor 31 are connected to the input terminal 300 and the input point of the current mirror circuit 1, respectively. do.

The operation of the embodiment configured as above will be explained below.

First, when a voltage signal is applied to the input terminal 300, it is converted into a current signal by the resistor 30 and flows out from the input point of the current mirror circuit 1. Here, the voltage applied to the input terminal 300 of the voltage-current converter 3 is
V ₃₀₀ , the voltage between the base and emitter of the transistor 31 is V _BE , and the resistance value of the resistor 30 is R ₃₀ .
Transistor 3 which is the output of voltage-current conversion circuit 3
The collector current Ic ₃₁ of 1 is expressed by the following equation.

Ic ₃₁ = V ₃₀₀ −V _BE /R ₃₀ …(2) On the other hand, the current flowing through the resistor 20 is the current flowing through the transistor 3.
Since the input current Iin of the current mirror circuit 1 does not depend on the collector current Ic ₃₁ of the current mirror circuit 1, the input current Iin of the current mirror circuit 1 decreases when Ic ₃₁ increases. That is, the input current Iin of the current mirror circuit 1 in this embodiment is the difference between equations (1) and (2), and is expressed by the following equation.

Iin＝V ₂₀₀ /R ₂₀ −V ₃₀₀ /R ₃₀ −(1/R ₂₀ −1/R ₃₀ )V _BE
...(3) From this, if R ₃₀ is selected as R ₂₀ /2 < R ₃₀ < ∞, the temperature drift caused by the temperature effect on V _BE can be made smaller than the conventional example as shown by equation (1), and R ₃₀ It can be seen that this temperature drift can be reduced to zero by choosing = R ₂₀ .

Therefore, according to this embodiment, it is possible to correct the temperature drift occurring in the input current of the current mirror circuit.

Note that in the circuit of this embodiment, the collector voltage of the transistor 31 is limited by the voltage at the input point of the current mirror circuit 1 and is as low as approximately 0.7V.
Since the emitter voltage of transistor 3 depends on the input V ₃₀₀ of the voltage-current conversion circuit, increasing V ₃₀₀
1 is saturated. Therefore, the operating range of the V ₃₀₀ cannot be widened.

FIG. 4 is a circuit diagram showing another embodiment of the present invention. In FIG. 4, the voltage-current conversion circuit 3 is
Unlike the illustrated embodiment, a resistor 30 is connected to the input of the current mirror circuit 4 and the input terminal 300. In the current mirror circuit 4, the bases and emitters of a diode-connected transistor 40 and a transistor 41 are commonly connected.

The operation of the embodiment configured as above will be explained below.

First, when a voltage signal is applied to the input terminal 300, it is converted into a current signal by the resistor 30, flows into the diode-connected transistor 40 of the current mirror circuit 4, and is connected to the collector of the transistor 41, which is the output of the current mirror circuit 4. 4
A current equal to the current flowing into 0 flows.

Here, since the voltage at the input point of the current mirror circuit 4 is V _BE like the current mirror circuit 1, the output current Ic ₄₁ of the voltage-current conversion circuit 3 is equal to equation (2).

Therefore, this embodiment also has the effect of being able to correct the temperature drift that occurs in the input current of the current mirror circuit 1.

Furthermore, according to this embodiment, since the output transistor 41 of the voltage-current conversion circuit is constructed with its emitters grounded, saturation of the transistor 41 does not occur and the range of the input voltage V ₃₀₀ of the voltage-current conversion circuit can be widened.

Furthermore, the broadband amplifier of this embodiment has an input terminal 200.
Since it is possible to convert and amplify a voltage difference between

FIG. 5 is a diagram showing still another embodiment of the present invention.

5, the difference from the embodiment shown in FIG. 4 is that emitter follower transistors 25 and 35 are connected to resistors 20 and 30, respectively, in order to increase the input impedance of input terminals 200 and 300, and a current mirror circuit 1 and 4.

The current mirror circuit 1 includes a transistor 10 and resistors 50, 51 ₁ , 51 ₂ , ..., 51n whose ends are grounded to the respective emitters of n transistors 11 ₁ , 11 ₂ , ..., 11n whose collectors are commonly connected.
The bases of each transistor are connected in common, and the emitter of the transistor 12 is connected to a resistor 52 whose one end is connected to the base, and the base and collector of the transistor 12 are connected to the collector of the transistor 10 and the power supply terminal 900.
It is configured by connecting to each.

The configuration of the current mirror circuit 4 is basically the same as that of the current mirror circuit 1, and the output transistor 11
₁ , 11 ₂ ... 11n and resistors 51 ₁ , 51 ₂ , ... 51n
The transistor 41 and the resistor 61 corresponding to this are different.

The operation of the embodiment configured as above will be explained below.

First, in the current mirror circuit 1, a transistor 10 and n transistors 11 ₁ , 11 ₂ ,...,
11n have the same characteristics, and resistors 50, 51 ₁ , 51 ₂ ,..., 51n are connected to the emitter of each transistor.
take the same value, and when the base of each transistor is driven by transistor 12, 10, 11 ₁ , 11
An equal current flows through the collectors of the transistors ₂ , . . . , 11n.

Therefore, output terminal 1 of the current mirror circuit
₀₀ , a current of n·Iin flows in the same way as shown in FIG.

On the other hand, the voltage at the input point of current mirror circuit 1
Vin is the value of resistor 50, _R50 , transistor 10,
Letting the base-emitter voltage of 12 be V _BE , the following equation is obtained.

Vin=Iin・R ₅₀ +2V _BE …(4) Next, the operation of current mirror circuit 4 is basically the same as current mirror circuit 1, and since the current mirror circuit 4 has one output transistor, the input current Ic ₄₀ and output current Ic ₄₁ become equal.

Therefore, Ic ₄₁ is expressed by the following formula, assuming that the input voltage at the input terminal 300 is V ₃₀₀ , the resistance values of the resistors 30 and 60 are R ₃₀ and R ₆₀ , and the base-collector voltages of the transistors 35, 42, and 40 are V _BE . shown.

Ic ₄₁ = V ₃₀₀ −3V _BE /R ₃₀ +R ₆₀ …(5) On the other hand, the current I ₂₀ flowing through the resistor 20 is the input terminal 2
00 voltage to V ₂₀₀ and the base voltage of transistor 25 to V 200 .
Let the emitter voltage be V _BE , and from the relationship in equation (4), the following equation is obtained.

I ₂₀ = V ₂₀₀ −Iin×R ₅₀ −3V _BE /R ₂₀ …(6) Also, the input current Iin of current mirror circuit 1 is I ₂₀
and Ic ₄₁ , so the following equation can be found from equations (5) and (6).

Iin=1/R ₂₀ +R ₅₀・{V ₂₀₀ −R ₂₀ /R ₃₀ +R ₆₀・V ₃₀₀ −(
1 −R ₂₀ /R ₃₀ +R ₆₀ )・3V _BE } ...(7) From equation (7), if R ₃₀ + R ₆₀ is chosen to be R ₂₀ /2 < (R ₃₀ + R ₆₀ ) < ∞, the effect of V _BE will be reduced. Therefore, the resulting temperature drift can be corrected. Furthermore, it can be seen that this temperature drift can be reduced to zero by choosing R ₃₀ + R ₆₀ = R ₂₀ .

Therefore, according to this embodiment, temperature drift can be corrected even in a broadband amplifier using a base current correction type current mirror circuit and an emitter follower circuit that increases the input impedance.

Furthermore, there are effects similar to those of the embodiment shown in FIG.

〔Effect of the invention〕

According to the present invention, temperature drift occurring in the input current of the current mirror circuit can be corrected, so that a stable broadband amplifier circuit can be obtained.

[Brief explanation of drawings]

Fig. 1 is a diagram showing an embodiment of a wideband amplifier circuit according to the present invention, Fig. 2 is a diagram showing an amplifier circuit using a conventional current mirror circuit, and Fig. 3 is a diagram showing input/output characteristics of the conventional circuit. , FIG. 4 is a diagram showing another embodiment of the invention, and FIG. 5 is a diagram showing still another embodiment of the invention. 1... Current mirror circuit, 20... Resistor, 3
...Voltage-current conversion circuit.

Claims (1)

[Claims] 1. A current mirror circuit that performs amplification by current operation, and a first voltage-current conversion in which one end of a resistor is connected to the current input point of the current mirror circuit, and the other end of the resistor is used as an input terminal. and a second voltage-current conversion circuit connected to a current input point of the current mirror circuit, the second voltage-current conversion circuit having a temperature dependence equal to the input bias current of the current mirror circuit. A wideband amplifier circuit featuring: 2. The broadband amplifier circuit according to claim 1, wherein the second voltage-current conversion circuit is constructed of the same type of circuit as the first voltage-current conversion circuit.