JPH04334105A - Current source circuit - Google Patents

Abstract

PURPOSE:To prevent a temperature characteristic of an output current from being changed depending on a setting position of a variable resistor used for setting the output current. CONSTITUTION:The temperature characteristic of a current source 11 is set so that the relation of aapprox.=b/c is established, where (a) is a temperature characteristic of the current source 11 connecting to a collector of a 1st transistor (TR) Q1, (c) is a temperature characteristic of a variable resistor VR connecting to an emitter of a 2nd TR Q2 and (b) is a temperature characteristic proportional to the absolute temperature.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to analog integrated circuits, and more particularly to a current source circuit whose output current is adjusted by an externally provided variable resistor.

0002

[Prior Art] A circuit used to output a current that changes in proportion to the current value of a basic current source and is smaller than the current value of this current source includes a current mirror as shown in FIG. A pair of transistors Q91 forming the circuit,
Of Q92, transistor Q92 that constitutes the output section
A variable resistor V is connected between the emitter of the power supply terminal P91 and the power supply terminal P91.
A configuration in which R91 is inserted is used. Then, by adjusting the variable resistor VR91, the transistor Q
The ratio between the collector current of 92 and the current of constant current source 91 is set.

0003

[Problem to be Solved by the Invention] If the temperature characteristics of the internal resistance of the constant current source 91 used in the above configuration are similar to the temperature characteristics of the variable resistor VR91, which is an external element, the collector of the transistor Q92 The temperature characteristics of the current output from the IC are constant regardless of the setting position of the variable resistor VR91, but the resistance created inside the IC is created by a diffusion process or an ion implantation process, Temperature characteristics are positive values, and in general, the rate of change per 1° temperature ranges from several 100 ppm to several 100 ppm.
The value is 0 ppm. On the other hand, the temperature characteristics of the variable resistor VR91 provided externally will have a negative value when a carbon resistor is used;
The rate of change per degree is about -300 ppm. Therefore, if the setting position of the variable resistor VR91 changes, a significant change will occur in the temperature characteristics of the output current, resulting in a drop of 2000 ppm.
/°C could occur.

The present invention was devised to solve the above problems, and its purpose is to provide a current source circuit that can prevent the temperature characteristics of the output current from changing depending on the setting position of the variable resistor. It's about doing.

[0005]

[Means for Solving the Problems] In order to solve the above problems, a current source circuit of the present invention includes a first transistor whose emitter is connected to a power supply terminal and whose collector is connected to a current source, and one terminal of which is connected to a power supply terminal. The emitter is connected to the other terminal of the variable resistor, which is an external element connected to the terminal, and the first
a second transistor whose base is connected to the base of the transistor
When the temperature characteristic of the current source is a, the temperature characteristic proportional to absolute temperature is b, and the temperature characteristic of the variable resistor is c, the temperature characteristic of the current source is a.
Set to a value such that a≒b/c. Further, a constant current source is used as the current source.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a circuit diagram showing the electrical configuration of an embodiment of the present invention.

In the figure, the emitter of a first transistor Q1, the emitter of a transistor Q3, and one terminal of a variable resistor VR provided outside the IC are connected to a power supply terminal P at which a positive voltage appears. , the other terminal of the variable resistor VR is led to the emitter of the second transistor Q2 via a terminal T provided on the IC. The base of the first transistor Q1 is connected to the base of the second transistor Q1.
is connected to the base of transistor Q2, the base of transistor Q3, and the emitter of transistor Q4. The collector of the first transistor Q1 is connected to one terminal of a current source 11 that outputs a constant current (which is a current) and the base of the transistor Q4, and the collector of the first transistor Q1 is connected to the other terminal of the current source 11 and the base of the transistor Q4. The collector is grounded. The collector of the transistor Q3 and the collector of the second transistor Q2 are each sent out as an output.

In the above configuration, if the temperature characteristic of the constant current source 11 is a, the temperature characteristic proportional to the absolute temperature is b, and the temperature characteristic of the variable resistor VR11 is c, then the relationship between these is a≈b/ It is set to be c.

The operation of one embodiment of the present invention will be explained below.

Transistor Q4 has hfe of 100
The base current of each of the first and second transistors Q1 and Q2 and the base current of the transistor Q3 flow from the emitter of the transistor Q4 to the collector side.
Since the base current flowing to the current source 11 is only the base current of the transistor Q4, the transistor Q3 operates as a current mirror with extremely small error with respect to the first transistor Q1, and from its collector, the current of the current source 11 is transmitted. A current with a value very close to the current value is output.

On the other hand, regarding the second transistor Q2, its collector current is denoted by I2, the current of the current source 11 is I1, the value of the variable resistor VR is r, Planck's constant is K, the electron charge is q, and the absolute If the temperature is denoted by T, the current I2 is KXT/q X LN(I1) = K
The current value satisfies the relationship: XT/q X LN (I2) + I2 X r.

[0012] The temperature characteristics a, b, and c will be explained below, as well as the influence brought about by the relationship between these temperature characteristics.

[0013] Since the normal temperature is a little less than 300°K, the value b indicating the temperature characteristic proportional to the absolute temperature is b =
1/300 = 3333 ≒ 3400 ppm. Furthermore, since a carbon resistor is used as the variable resistor VR11, the temperature characteristic c becomes c=−300 ppm. Further, the temperature characteristic a of the constant current source 11 is a≒ b /
Since it is set to be c, a≒ (1+0
．． 0034) / (1-0.0003)≒ 1 +
0.0034 + 0.0003= 1 + 0.00
37, and its temperature characteristic a is about 3700 ppm. Therefore, the temperature characteristics of the current output to the collector of the transistor Q3 are the same as those of the current source 11, and the value thereof is 3700 ppm.

Furthermore, the temperature characteristic of the voltage between the base and emitter of the first transistor Q1 is such that the voltage is Vbe1.
Since it is shown as Vbe1 = KXT/q X LN (I1), 3400 ppm proportional to absolute temperature
(The change in the logarithmic part is an extremely small value change compared to the change in absolute temperature, so it can be ignored.) Furthermore, the temperature characteristic of the voltage between the base and emitter of the second transistor Q2 is such that the voltage is Vbe2
Since it is shown as Vbe2 = KXT/q X LN(I2), the temperature characteristic is 3400 ppm which is proportional to the absolute temperature, as in the case of the first transistor Q1 (ignoring the change in the logarithmic part). ).

Furthermore, if the temperature characteristic of the voltage between the terminals of the variable resistor VR is expressed by y, then it is expressed as y = a × c, and since a = b / c, it is expressed as y = b, The temperature characteristic of the voltage between the terminals of the variable resistor VR is 340, which is a value proportional to the absolute temperature.
It becomes 0ppm.

This means that no matter what value the variable resistor VR is set to, the voltage between the base emitter of the first transistor Q1 and the second transistor Q
The ratio of 2 to the base-emitter voltage means that even if the temperature changes, as long as the setting of the variable resistor VR is kept constant, its value will remain constant. . Therefore, the temperature characteristic of the current output from the collector of the second transistor Q2 is equal to the temperature characteristic of the current source 11, and its value is 3700 ppm. In other words, although the output of the transistor Q3 and the output of the second transistor Q2 have different current values, their temperature characteristics are the same, 3700 ppm.

It should be noted that the present invention is not limited to the above embodiment, and the variable resistor VR has a temperature characteristic of -300pp.
Although the case where the temperature characteristic is m has been described, it is possible to similarly apply the case where the temperature characteristic has other values.

Further, although the current source 11 has been described as a constant current source, it can be similarly applied to a current source whose output current value changes.

Furthermore, the four transistors Q1 to Q4 include
Although we have explained the case using PNP transistors,
The present invention can be similarly applied to a case where an NPN transistor is used.

[0020]

Effects of the Invention In the current source circuit according to the present invention, the temperature characteristic of the variable resistor, which is an external element connected between the emitter of the transistor in the output section constituting the current mirror circuit and the power supply terminal, is c. The temperature characteristic proportional to the absolute temperature is b
When the temperature characteristic of the current source that sets the current value of the current mirror circuit is a, the value of the temperature characteristic a is a≈b/
Since the value is set to c, the temperature characteristic of the voltage between the terminals of the variable resistor becomes a temperature characteristic proportional to the absolute temperature. Therefore, regardless of the setting position of the variable resistor, the temperature characteristics of the output current of the second transistor will match the temperature characteristics of the current source, and the temperature characteristics of the output current will change depending on the setting position of the variable resistor. This makes it possible to prevent

[Brief explanation of drawings]

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

FIG. 2 is a circuit diagram showing the electrical configuration of the prior art.

[Explanation of symbols]

11 Current source Q1 First transistor Q2 Second transistor P Power supply terminal VR variable resistor

Claims (2)

[Claims] 1. A first transistor having an emitter connected to a power supply terminal and a collector connected to a current source, and the other terminal of a variable resistor being an external element having one terminal connected to the power supply terminal. a second transistor whose emitter is connected and whose base is connected to the base of the first transistor, the temperature characteristic of the current source is a, the temperature characteristic proportional to absolute temperature is b, and the variable When the temperature characteristic of the resistor is c, the temperature characteristic of the current source is a
A current source circuit characterized in that a=b/c. 2. The current source circuit according to claim 1, wherein the current source is a constant current source.