JPH04223609A - Shunt control circuit - Google Patents

Abstract

PURPOSE:To obtain a shunt control circuit by which the shunt ratio of a shunt which is set one time by a control voltage V can be held to be constant regardless of a temperature change. CONSTITUTION:The control voltage V is supplied through first and second emitter follower circuits constituted of pnp transistors Q12 and Q13 which are the reversed polarities of transistors Q4 and Q5 to a differential circuit constituted of the npn transistors Q4 and Q5, resistances R6 and R7, and power source 14. And also, the collector currents Ic4 of the transistor Q4 are supplied through the first current mirror circuit constituted of transistors Q8 and Q9, and resistances R8 and R9 to the transistor Q12, as a current source. Moreover, the collector currents Ic5 of the transistor Q5 are supplied through the second current mirror circuit constituted of transistors Q10 and Q11, and resistances R10 and R11 to the transistor Q13 as the current source. Thus, the temperature characteristic of the shunt can be made to be zero.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to shunt control circuits. In particular, it is an object of the present invention to provide a shunt control circuit that controls a shunt so that the shunt ratio is always constant regardless of temperature fluctuations.

0002

2. Description of the Related Art FIG. 3 shows a general flow divider. The circuit configuration of the illustrated shunt is such that the respective emitters of the first npn transistor Q1 and the second npn transistor Q2 are connected, and the signal current source 13 is connected to this connection point. In this shunt, the signal current source 13
The input signal current Io supplied from the transistor Q
The collector currents Ic1 and Ic2 of the transistors Q1 and Q2 are divided in accordance with the voltage ΔV between the bases of the differential pair formed by the transistors Q1 and Q2. And transistor Q
By controlling the base-to-base voltage ΔV of Q1 and Q2 from the outside, the shunt ratio of the collector currents Ic1 and Ic2 can be changed. At this time, each collector current Ic1, Ic
2 is expressed by the following equation (1).

0003

[Math 1]

[0004] If the division ratio n is defined as n=Ic1/Io, then the division ratio n is

[0005]

[Math 2]

It can be expressed as [0006]. As can be seen from this equation (2), the current division ratio n can be controlled by the base-to-base voltage (control voltage) ΔV. As shown in FIG. 4, the control voltage ΔV is generally applied by dividing an external voltage using resistors R1 and R2. Next, consider the temperature characteristics of the split flow ratio n. By differentiating equation (2) with respect to temperature T, temperature characteristics can be obtained.

[0007]

[Math 3]

From equation (3), n=0.5 (that is, △V=
Temperature characteristics (1/n) only when the equilibrium state is 0)
dn/d T becomes zero. When n is other than 0.5, the division ratio n has temperature characteristics.

FIG. 5 shows an example in which a current shunt is applied to a gain control circuit. In this example, a signal current source is configured by the transistor Q3, the resistor R3, and the voltage source Vin. The illustrated gain control circuit has a gain Vout by a control voltage ΔV.
/Vin control. This circuit also has the disadvantage that, due to the above-mentioned temperature characteristics of the shunt, the gain once set by the control voltage ΔV fluctuates due to temperature changes even without changing the control voltage ΔV. The control characteristic of △V vs. n (control characteristic of the shunt ratio) of the above-mentioned shunt is expressed by the formula (2)
As shown in , since the term exp is dominant, the characteristic is non-linear. FIG. 6 shows a conventional shunt control circuit in which this control characteristic has been improved to have excellent linearity. The shunt ratio n=Ic1/Io of the shunt composed of transistors Q1 and Q2 shown in the figure is:

0010

[Math 4]

[0011] Here, npn transistor Q
4, Q5, resistors R6, R7, current source 15 (current value I1
) is the shunt ratio of the differential pair circuit consisting of n1 = Ic4/
I1, equation (4) becomes (I1 = Ic4+Ic
5)

0012

[Math 5]

[0013] On the other hand, the relationship between the base-to-base voltage (control voltage) ΔV of the differential pair circuit and the shunt ratio n1 is R6
=R7, then

[0014]

[Math 6]

It is expressed as follows. Therefore, equation (5), equation (6)
Therefore, the relational expression between the control voltage △V and the shunt ratio n is given by the following expression (7
).

[0016]

[Math 7]

As is clear from equation (7), the control characteristics of the shunt equipped with the shunt control circuit shown in FIG.
6, the current shunt has better linearity than the shunt shown in FIG. 4, and the larger the resistance R6, the better the linearity. Next, the temperature characteristics (1/n) dn/ of the flow divider in FIG.
When finding dT,

[0018]

[Math. 8]

[0019] However, the temperature characteristic of the control voltage ΔV is assumed to be zero. Here, if the current source 15 is given a temperature characteristic of resistance, the second term of equation (8) becomes zero, and the temperature characteristic (
1/n)dn/dT is expressed as the following equation (9).

[0020]

[Math. 9]

As is clear from equations (8) and (9),
This shunt also has a temperature characteristic (1/n) dn/only when the shunt ratio n=0.5 (that is, in the equilibrium state of ΔV=0)
d T becomes zero. However, other than n=0.5, (
1/n) dn/d T does not become zero, and the division ratio n has temperature characteristics. Therefore, in the shunt control circuit shown in FIG. 6, the shunt ratio of the shunt cannot be kept constant regardless of temperature changes.

[0022]

[Problems to be Solved by the Invention] The problem to be solved by the present invention is to provide a shunt control circuit that can maintain the shunt flow ratio, once set by the control voltage △V, constant regardless of temperature changes. The question is what measures should be taken to achieve this.

[0023]

[Means for Solving the Problems] Therefore, in order to solve the above problems, the present invention provides that the respective emitters of a first transistor and a second transistor are connected, a signal current is input to this connection point, A shunt control circuit that controls a shunt that varies the collector currents of the first and second transistors by changing the voltage applied to the bases of the first and second transistors. a first transistor comprising a third transistor whose base is connected to the first external control voltage input terminal;
a second emitter follower circuit composed of a fourth transistor whose base is connected to the second external control voltage input terminal; an emitter of the fifth transistor and one end of the first resistor; are connected, the other end of the first resistor and one end of the second resistor are connected, the other end of the second resistor and the emitter of the sixth transistor are connected, and the first resistor and a differential pair circuit configured with a current source connected to a connection point with the second resistor; means for connecting the emitter of the third transistor and the base of the fifth transistor; means for connecting the emitter of the fourth transistor and the base of the sixth transistor, the base being connected to a voltage source and the emitter being connected to the base of the first transistor and the collector of the fifth transistor; a seventh transistor; an eighth transistor having a base connected to the voltage source and an emitter connected to the base of the second transistor and the collector of the sixth transistor; and a collector current of the seventh transistor. a first current mirror circuit that supplies the collector current of the eighth transistor to the first emitter follower circuit as a current source; and a second current mirror circuit that supplies the collector current of the eighth transistor to the second emitter follower circuit as a current source. and the first and second
, the fifth, sixth, seventh, and eighth transistors have the same polarity, the third and fourth transistors have opposite characteristics to the first transistor, and the third and fourth transistors have opposite characteristics to the first transistor, and The present invention provides a shunt control circuit characterized in that the current source connected to the connection point between the first resistor and the second resistor has a temperature characteristic opposite to that of the resistance.

[0024]

Embodiment FIG. 1 shows an embodiment of the present invention. The same parts as in the conventional example are given the same reference numerals, and detailed explanations of those parts will be omitted. The characteristics of the shunt control circuit shown in FIG.
, to a differential pair circuit composed of a current source 14 (current value I1), through first and second emitter follower circuits composed of pnp transistors Q12 and Q13 having opposite polarity to transistors Q4 and Q5, Supply control voltage △V. In addition, the collector current Ic4 of the transistor Q4 is
It is supplied as a current source to the transistor Q12 via a first current mirror circuit composed of pnp transistors Q8 and Q9 and resistors R8 and R9. Furthermore, the collector current Ic5 of the transistor Q5 is changed to a second
This is to supply the current to the transistor Q13 as a current source through the current mirror circuit.

Next, the circuit configuration of this shunt control circuit will be explained in detail. The first emitter follower circuit is composed of a third transistor Q12 whose base is connected to the first external control voltage input terminal 11. The second emitter follower circuit has a second external control voltage input terminal 12.
The fourth transistor Q13 has a base connected to the fourth transistor Q13. A control voltage ΔV is applied between external control voltage input terminals 11 and 12. In the differential pair circuit, the emitter of the fifth transistor Q4 is connected to one end of the first resistor R7, and the other end of the resistor R7 is connected to one end of the second resistor R6. Further, the other end of the resistor R6 is connected to the emitter of the sixth transistor Q5, and a current source 14 (current value I1) is connected to the connection point between the resistors R7 and R6. In this way, the differential pair circuit is configured.

The emitter of the third transistor Q12 and the base of the fifth transistor Q4 are connected. Further, the emitter of the fourth transistor Q13 and the base of the sixth transistor Q5 are connected. The seventh transistor Q6 has a base connected to the voltage source V1 and an emitter connected to the base of the first transistor Q1 in the shunt and the collector of the fifth transistor Q4. The eighth transistor Q7 has a base connected to the voltage source V1 and an emitter connected to the base of the second transistor Q2 in the shunt and the sixth transistor Q7.
It is connected to the collector of transistor Q5.

The first current mirror circuit is composed of transistors Q8 and Q9 and resistors R8 and R9. The collector of the transistor Q9 is connected to the seventh transistor Q.
The collector of the transistor Q8 is connected to the emitter of the third transistor Q12. With this connection, the first current mirror circuit can control the collector current of the seventh transistor Q6 (i.e., the collector current Ic4 of the fifth transistor Q4).
is supplied to the first emitter follower circuit as a current source. The second current mirror circuit is composed of transistors Q10 and Q11 and resistors R10 and R11. The collector of the transistor Q10 is connected to the collector of the eighth transistor Q7, and the collector of the transistor Q10 is connected to the collector of the eighth transistor Q7.
The collector of transistor Q1 is connected to the emitter of the fourth transistor Q13. With this connection, the second current mirror circuit supplies the collector current of the eighth transistor Q7 (that is, the collector current Ic5 of the sixth transistor Q5) to the second emitter follower circuit as a current source. ing.

[0028] The first, second, fifth, sixth, seventh, and eighth
Each transistor Q1, Q2, Q4, Q5, Q6, Q7
are npn transistors with the same polarity, and the third and fourth transistors Q12 and Q13 are pnp transistors with opposite characteristics to those of the first transistor Q1. Further, the current source 14 connected to the connection point between the first resistor R7 and the second resistor R6 has a temperature characteristic opposite to that of the resistance. By configuring the shunt control circuit as described above, collector currents Ic4 and Ic5 of transistors Q4 and Q5 can be obtained from the following equation (10).

[0029]

[Math. 10]

From formula (10),

[0031]

[Math. 11]

[0032] Substituting equation (5) into equation (11) yields equation (12) below.

[0033]

[Math. 12]

Therefore, by differentiating equation (12) with respect to temperature, the temperature characteristics of the shunt controlled by this shunt control circuit can be determined. The temperature characteristics are shown in the following equation (13).

[0035]

[Math. 13]

However, the temperature characteristic of the control voltage ΔV is assumed to be zero. Therefore, from equation (13), if a current source 14 having temperature characteristics opposite to that of the resistance is used, the temperature characteristics (1
/n) dn/d T can be made zero. FIG. 2 shows an example of the current source 14 having temperature characteristics of resistance. This current source 1
4 are npn transistors Q20, Q22, Q23,
pnp transistor Q21 and resistors R20 to R25
The collector of the transistor Q23 serves as the output terminal. The output current I1 of the current source 14 is obtained from the following equation (14). (However, R24=R25.)

[0037]

[Math. 14]

Therefore, the temperature characteristics of the current source 14 (1/I
1) dI1/dT is

[0039]

[Math. 15]

##EQU1## Substituting this equation (15) into equation (13) results in (1/n)dn/d T=0, and this shunt control circuit can make the temperature characteristics of the shunt to zero.

[0041]

As described above, the shunt control circuit of the present invention can control the shunt so that the temperature characteristics of the shunt are zero. Therefore, the shunt controlled by this shunt control circuit can maintain the shunt ratio, once set by the control voltage ΔV, constant regardless of temperature changes.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing an example of a current source used in the example.

FIG. 3 is a diagram showing a conventional general flow divider.

FIG. 4 is a diagram showing a conventional general flow divider.

FIG. 5 is a diagram showing a conventional gain control circuit using a shunt.

FIG. 6 is a diagram showing a conventional shunt control circuit.

[Explanation of symbols]

11 First external control voltage input terminal 12 Second external control voltage input terminal 13 Signal current source 14 Current source Q1 First transistor Q2 Second transistor Q4 Fifth transistor Q5 6th transistor Q6 Seventh transistor Q7 Eighth transistor Q12 Third transistor Q13 Fourth transistor R6 Second resistor R7 First resistance

Claims (1)

[Claims] 1. Emitters of each of a first transistor and a second transistor are connected, a signal current is input to this connection point, and a voltage is applied to each base of the first and second transistors. A shunt control circuit that controls a shunt that varies the collector current of each of the first and second transistors by changing the voltage, the base of which is connected to a first external control voltage input terminal. a first emitter follower circuit constituted by a third transistor; a second emitter follower circuit constituted by a fourth transistor whose base is connected to the second external control voltage input terminal; and a fifth transistor. The emitter of the first resistor is connected to one end of the first resistor, the other end of the first resistor is connected to one end of the second resistor, and the other end of the second resistor is connected to the emitter of the sixth transistor. are connected to each other, and a current source is connected to a connection point between the first resistor and the second resistor, the emitter of the third transistor, and the fifth transistor. means for connecting the emitter of the fourth transistor and the base of the sixth transistor; the base is connected to a voltage source; the emitter is connected to the base of the first transistor and the base of the sixth transistor; a seventh transistor connected to the collector of the fifth transistor; and an eighth transistor having a base connected to the voltage source and an emitter connected to the base of the second transistor and the collector of the sixth transistor. a first current mirror circuit that supplies the collector current of the seventh transistor to the first emitter follower circuit as a current source; and a first current mirror circuit that supplies the collector current of the seventh transistor to the second emitter follower circuit;
a second current mirror circuit that supplies the emitter follower circuit as a current source to the emitter follower circuit of the first, second, fifth, and
The sixth, seventh, and eighth transistors are transistors of the same polarity, and the third and fourth transistors are transistors with opposite characteristics to those of the first transistor,
A shunt control circuit, wherein the current source connected to a connection point between the first resistor and the second resistor has a temperature characteristic opposite to that of the resistance.