JPS63100520A - Constant current source circuit - Google Patents

Abstract

PURPOSE:To suppress the influences of characteristic variance and dependency upon the temperature of transistors TRs by converting the output current of a second TR to a voltage and controlling the output current to the load of a first TR based on the result of comparison between this voltage and a reference voltage. CONSTITUTION:The drain current I'D of a TR M2 is converted to a voltage by a resistance R1 in a current detecting circuit 1, and the voltage between both ends of the resistance and the reference voltage from a reference voltage generating circuit 2 are compared with each other by a comparator A1. If the voltage between both ends of the resistance R1 is lower than the reference voltage, the output of the comparator A approximates the earth voltage. The output voltage of the comparator A1 discharges the electric charge stored in a capacitor C1. Consequently, the voltage between both ends of a capacitor C1 is reduced and acts in such direction that voltages between gates and the sources of TRs M1 and M2 are increase between gates and the sources of TRs M1 and M2 are increased, and the respective drain currents of TRs M1 and M2 are increased. This operation is continued until the voltage between both ends of the resistance R1 and the reference voltage are equal to each other.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a constant current source circuit suitable for MO8IC implementation.

[Conventional technology]

Conventionally, the MO8IC process has been used exclusively for digital ICs, but with advances in circuit technology, it is also being used in the analog field. Also in the constant current source circuit, M:
) SIC process has come into use, an example of which is shown in FIG. The figure shows a constant current source circuit using a conventionally well-known fixed bias method, where Ml is a P-channel MO8FET (hereinafter simply referred to as a transistor), R1°R,, R, are resistors, and ■, are The voltage source Ii and the drain current VG of transistor M are the gate-source voltage of transistor M1. Further, FIG. 4 shows the static characteristics of the gate-source voltage VG8 versus drain current ID of the transistor M shown in FIG. 3.

As is clear from FIG. 4, if the gate-source voltage vGa of the transistor M1 is constant, the drain current ID also becomes -7''i, regardless of the resistance value of the load resistor island. The gate voltage of M1 is resistor R,,
It is determined by the resistance ratio of R and the voltage of the power supply v1. Therefore, if the voltage of the power supply v1 is constant, the transistor M,
The gate-source voltage Vo8 is kept constant, and the transistor M1 operates as a constant current source.

[Problem that the invention seeks to solve]

By the way, when converting such an analog circuit into an Al08 IC, it is generally manufactured using the same process as when converting into a digital IC in order to reduce costs.

However, in such a semiconductor manufacturing process, large variations occur in the gate-source voltage vs. drain current characteristics of transistors, and transistors have greater temperature dependence and poor temperature characteristics than resistors, capacitors, etc. In the above conventional technology, variations in transistor characteristics and @
There was a problem in that the current value of the constant current source fluctuated greatly (usually M:2 in the SIC process) because no consideration was given to temperature fluctuations.

SUMMARY OF THE INVENTION An object of the present invention is to provide a constant current source circuit that can suppress the effects of variations in transistor characteristics and temperature dependence.

[Means for solving problems]

In order to achieve the above object, the present invention provides a second transistor so as to form a current mirror with a first transistor that supplies current to a load, converts the output current of the second transistor into a voltage, The output tIL flow of the first transistor to the load is controlled based on a comparison result between the voltage and a reference voltage.

[Effect]

The output current of the second transistor is equal to the first output current. The output current of the second transistor is controlled so that the voltage due to the output current of the second transistor is equal to the reference voltage. The output 'gL current of the first transistor is held at a constant current value determined by the reference voltage.

The reference voltage is constant, so even if the first and second transistors have large variations in characteristics or temperature dependence, their output currents are determined by the reference voltage and are independent of variations in characteristics or temperature dependence. It is not affected by gender.

- [Example] Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram showing an embodiment of a constant current source circuit according to the present invention, in which 1 is a current detection circuit, 2 is a reference voltage generation circuit, 3 is a comparison circuit, and M+9Mz is a P-channel MO8F.
ET (hereinafter simply referred to as transistor).

V, , V is a voltage source, current is a resistor, CI is a capacitor; A1 is a comparator.

In the figure, a transistor M1 operates as a constant current source transistor with a resistor R as a load.A male current detection circuit 1 is a transistor N1! , a resistor &, and the transistor M has the same polarity as the transistor M, and forms a current mirror structure with the transistor M. Therefore, the drain current ID of transistor M1 is equal to the drain current IID of transistor 84. The drain current rD of the transistor gull is supplied to the resistance layer. Here, the drain current fo1kID of the transistor gull, ,
If the resistance value of the resistive layer is r, then the voltage VRI across the resistor is VRI = ID1 ・rl ・+ ++ (11, the drain current I of the transistor M, and the voltage across the resistive layer It can be detected as VR1.

The reference voltage generation circuit 2 is a voltage source V! It generates a constant voltage (hereinafter referred to as reference voltage) represented by the product of the resistance value r1 of the resistor and the current flowing through the transistor M.

The comparison circuit 3 consists of a comparator A1, and the reference voltage generation circuit 2
The reference voltage generated by the current detection circuit 1 is compared with the voltage RI across the resistance layer of the current detection circuit 1, and the difference voltage is output. Here, when the two input voltage levels of comparator A are equal, the output impedance becomes a high impedance state.

Capacitor C1 accumulates the differential voltage output from comparator circuit 3.

Next, this example will be explained.

In the tfi detection circuit 1, the train current I'D of the transistor A is converted into a voltage Kf by a resistive layer, and the voltage across this resistive layer is compared with the reference voltage from the reference voltage generating circuit 2 in the comparator A1. Here, when the voltage across the resistance layer is smaller than the reference voltage, the output of the comparator A1 becomes a voltage close to the ground voltage.

The output voltage of comparator A1 discharges the charge stored in capacitor C1. As a result, the voltage across the capacitor C1 decreases, acting to increase the gate-source voltage of the transistors M, , M, and
The respective drain currents of l*M@ are added together.

The above operation continues until the voltage across the resistor becomes equal to the reference voltage.

Next, when the voltage across the resistor and the reference voltage are equal, the output of the comparator A becomes a zero impedance state, and the voltage across the capacitor C1 becomes a held state. This causes the transistor MI.

The gate-source voltage of M is kept constant, and the drain currents of transistors M, M1, and Ml each have a constant value. That is, transistor M1 operates as a constant current source.

On the other hand, when the voltage across the resistor is higher than the reference voltage, the comparator A1 outputs a voltage close to the power supply voltage. This is K
As a result, the voltage tJ''- across the capacitor CI becomes higher, which acts in the direction of reducing the gate-source voltage of the transistor stripes and stripes, and reduces the drain current of each transistor Ml+M. This continues until the voltage across & becomes equal to Kishin Denoh.

As described above, this embodiment constitutes a constant current source circuit that is not affected by variations in transistor characteristics and temperature fluctuations.

Since the resistor RL is used as a load for the current source transistor M1, it is clear that an active element such as a transistor may be used instead of the resistor RL.

FIG. 2 is a circuit diagram showing another embodiment of the constant current circuit according to the present invention, in which AI, , M are O8FE between N channels.
T, V, are voltage sources, v4 is a reference voltage source, and the first
Components having the same functions as those in the figures are given the same reference numerals.

Since the operation of this embodiment can be more easily understood than the explanation of the operation of the embodiment shown in FIG. 1, the explanation thereof will be omitted. This embodiment also constitutes a constant current source circuit that is not affected by variations in characteristics of MO8F'ET and temperature fluctuations.

Note that since the resistor circle is used as a load for the current source MO8FBTM, it is clear that an active element such as a K MOSFET may be used instead of the resistor RL.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to provide a constant current source circuit that does not have variations in t-current or fluctuations in the current source due to variations in the characteristics of MOSFETs due to the manufacture of ICs and changes in characteristics due to temperature fluctuations. Can be done.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing one embodiment of the constant current source circuit according to the present invention, FIG. 2 is a circuit diagram showing another embodiment of the constant current source circuit according to the present invention, and FIG. 3 is a constant current source circuit. FIG. 4 is a circuit diagram showing one conventional example, and FIG. 4 is a diagram showing an example of characteristics of a MOSFET. Ml, seagull 01. P channel MO8F ET, Ms
0M4...N channel O8FET, R,,
R1...Resistance, C1...Conte's representative patent attorney small
Katsuo Kawa゛Figure 1 Figure 27

Claims (1)

[Claims] 1. A first transistor for constant current supplying current to a load, a second transistor forming a current mirror with the first transistor, and a resistor to which the output current of the second transistor is supplied; comprising a comparator circuit that compares the voltage across the resistor with a reference voltage, and controls the output currents of the first and second transistors with the output voltage of the comparator circuit;
A constant current source circuit characterized in that the output current of the first transistor can be held constant.