JPS63100519A - Constant current source circuit - Google Patents

Abstract

PURPOSE:To suppress the variance of current due to the characteristic variance and the temperature characteristic of transistors TRs by detecting the drain current conducted to a TR operated as a current source and controlling the gate voltage of the TR so that the drain current is constant. CONSTITUTION:The drain current of a TR M2 is converted to a voltage by a capacitor C1, and the voltage between both ends of the capacitor C1 is sampled and held by a capacitor C2 of a sample/hold circuit 6. The sampled/held voltage is compared with the reference voltage of a reference voltage generating circuit 7 by the amplifier A2 of a comparator 8. If the voltage between both ends of the capacitor C2 is lower than the reference voltage, the output of the amplifier A2 approximates the earth voltage. The output of the amplifier A2 discharges the electric charged stored in a capacitor C3 of a smoothing circuit 9. Consequently, the voltage between both ends of the capacitor C3 is reduced and it is operated in such direction that voltages between gates and sources of TRs M1 and M2 are increased, and respective drain currents of TRs M1 and M2 are increased.

Description

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

[Prior Art] Various constant current source circuits using semiconductor elements have been proposed and put into practical use.

FIG. 6 is a circuit diagram for explaining a constant current source circuit using a conventional fixed bias method, in which Ml is a P-channel M
O8, FET (hereinafter abbreviated as transistor M1)
, 2 is a bias circuit, 3 is a power supply (vl), 4 is a load resistance, FLt, HI3 is a resistor, ID is a transistor Ml
The drain current VO2 flowing through the transistor M1 is the gate-source voltage of the transistor M1.

FIG. 7 is a static characteristic diagram of the gate-source voltage Voa and drain current ID of the transistor M1 in the circuit of FIG.

As can be seen from the static characteristic diagram in FIG. 7, if the gate-source voltage Vos of the transistor 4M1 is constant.

The drain current ID is also constant, and a constant current ID flows regardless of the magnitude on the load resistance. Here, the gate voltage of the transistor M+ is the resistance ratio of the resistor R1, the resistance ratio of the resistor 2, and the power supply S.
It is determined by the voltage v1 of .

Therefore, if the voltage v1 of the power supply 3 is constant, the gate-source voltage Vos of the transistor M1 is kept constant, and the transistor M1 operates as a constant current source.

However, in the above-mentioned conventional technology, there are manufacturing variations and temperature dependence in the gate-source voltage Vow vs. drain current ID% of the transistor M1, and fluctuations in the drain current caused by these are not taken into consideration. There wasn't.

- [Problems to be Solved by the Invention] As mentioned above in 51C, there are large variations in the characteristics of transistors in the semiconductor manufacturing process. Also, transistors have poor temperature characteristics compared to resistors and capacitors.

In the above-mentioned conventional technology, no consideration is given to variations in the characteristics of the transistors and temperature fluctuations, and the current value of the constant current source fluctuates greatly (usually MO8).

In the IC process, there was a problem of 2 times to 1/2).

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

[Means for solving problems]

The above objective is achieved by detecting the drain (collector) current ID flowing through the transistor M1, which operates as a current source, and controlling the gate (base) voltage of the transistor M1 so that the drain (collector) current ID is constant. be done.

The drain of transistor M1 (first transistor) (
In order to detect the current (collector), the transistor M1
a second transistor paired with a second transistor, a first capacitor connected to the drain (collector) side of the second transistor and whose other end is grounded; and a first capacitor connected in parallel to the first capacitor. A current mirror circuit is formed by these and the transistor M1° resistor. The first switch discharges the charge of the first capacitor at regular intervals. A sample-and-hold circuit is provided that samples and holds the voltage across the first capacitor for a certain period of time in synchronization with the operation of the first switch, and the sample-and-hold circuit samples and holds the voltage across the first capacitor for a certain period of time.
The magnitude of the drain (collector) current of the second transistor is determined by comparing the drain current of the transistor with a voltage preset by the capacitance value of the first capacitor. This is achieved by controlling the (base) voltage, that is, the gate (base) voltage of transistor M1.

[Effect]

In the current detection circuit, the first switch discharges the charge of the first capacitor at regular intervals.

stored in the first capacitor. Through these operations, the drain (collector) current flowing through the second transistor can be detected from both ends of the first capacitor in a voltage-converted state.

The sample and hold circuit samples and holds the voltage across the first capacitor in synchronization with the first switch. The base voltage generation circuit generates a constant voltage (reference voltage). The comparison circuit compares the output voltage of the sample-and-hold circuit and the reference voltage of the normalized voltage generation circuit, and outputs a voltage (or current) according to the difference between these voltages. A smoothing circuit smoothes the output voltage of the comparison circuit. By applying the smoothed voltage to the gate (base) of the second transistor,
Drain (collector) currents of the second transistor and the transistor Ml (first transistor) operating as a current source can be controlled. That is, the transistor MS (first transistor) and the second
drain (collector) of the transistor? ! Since the current is determined by the capacitance i of the first capacitor of the current detection circuit, the sampling time of the sample-and-hold circuit, and the reference voltage of the reference voltage generation circuit, the transistor M
A constant value of current can be obtained regardless of characteristic fluctuations.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram showing a first embodiment of a constant current source circuit according to the present invention, in which Mz and Mz are P-channel MO8 and FET (hereinafter abbreviated as transistor), respectively.

Vl and V2 are each a voltage source, Rt is a resistance, RL is a load resistance, C1, C'2, and Cs are each a capacitor,
Sl and S2 are switch circuits, At and Ax, respectively.
each indicates an amplifier.

Further, 5 is a current detection circuit, 6 is a sample/hold circuit, 7 is a reference voltage generation circuit, 8 is a comparison circuit, and 9 is a smoothing circuit.

FIG. 2 is an operating waveform diagram of FIG. 1, where (α) is the conduction state of the switch circuit S1, (b) is the conduction state of the switch circuit S2, (C) is the voltage waveform at point X, and (d) is the conduction state of the switch circuit S2. shows the voltage waveform at point Y.

First, the individual operations of each part will be explained.

In FIG. 1, the transistor M1 operates as a current source with a resistor as a load. Next, the current detection circuit 5
I will explain about it. The switch circuit S1 discharges the charge of the capacitor C1 at regular intervals.

Transistor M2 uses capacitor C1 as a load.

It has a current mirror configuration with transistor M1.

Therefore, the drain current of transistor M2 is proportional to the drain current of transistor M1. The transistor M
2, the drain current of switch circuit S1 is non-conducting (OF
F) flows into capacitor C1 when the current is in state F). At this time, the drain current of transistor M2.

can be detected as the voltage across capacitor C1.

The sample/hold circuit 6 converts the voltage across the capacitor C1 of the current detection circuit 5 into a capacitor C2 by a switch circuit S2 operating in synchronization with the switch circuit S1.
sample and hold.

Amplifier A1 operates as an impedance converter. Here, the capacitance of the capacitor C1 of the current detection circuit 5 is C+,) the drain current of the transistor M2 is In2,
If the time during which the switch circuit S2 is conductive is t2, then
The voltage Vo across capacitor C2 can be expressed as the voltage across capacitor C2, and the drain current of transistor M2 can be expressed as the voltage across capacitor C2.

The reference voltage generation circuit 7 generates a constant voltage (hereinafter referred to as a reference voltage) that is equal to the drain current 11)2K of the transistor M2 based on the relationship of equation (1).

A comparison circuit 8 compares the reference voltage generated by the reference voltage generation circuit 7 and the sample hole.

The voltage stored in the capacitor C2 of the code circuit 6 is compared with the voltage stored in the capacitor C2, and the result is output as a voltage. here,.

The output impedance of the amplifier A2 becomes a high impedance state when the two comparison signal levels are equal.

The smoothing circuit 9 smoothes the output voltage output from the comparison circuit 8.

Next, the overall operation will be explained.

The drain current of the transistor M1 is represented by the drain current of the transistor M2 of the current detection circuit 5. After the drain current of the transistor M2 is converted into a voltage by the capacitor C1, the voltage across the capacitor C1 is sampled. - Sampled and held by capacitor C2 of hold circuit 6. The sampled and held voltage is supplied to the reference voltage generation circuit 7 by the amplifier A2 of the comparator circuit 8.
0 reference voltage. Here, considering the case where the voltage across the capacitor C2 is smaller than the reference voltage, the output of the amplifier A2 becomes a voltage close to the ground voltage. The amplifier A2
The output of is the capacitor C! of the smoothing circuit 9. performs an operation to discharge the charges accumulated in the This makes the capacitor C
The voltage across the transistor M+ becomes smaller.

It operates in the direction of increasing the gate-source voltage of Mz. That is, the drain current of each transistor M10Ml is increased.

Next, consider the case where the reference voltage and the voltage across capacitor C2 are equal. At this time, the output of the amplifier A2 becomes a high impedance state, and the voltage across the capacitor Cs of the smoothing circuit becomes a held state. During this time, transistor M1. M! The gate-source voltage of 11. is kept constant to the transistor. 8] The drain current of each of 2 becomes a constant value.

Next, consider the case where the voltage across the capacitor C2 is higher than the reference voltage. At this time, the amplified speaker! outputs a voltage close to the power supply voltage.

This causes the voltage across capacitor C1 to rise and transistor M1. It operates in the direction of reducing the gate and source of Mz. That is, transistor M1.
Decrease the drain current of each Ml.

Fluctuations in the output of the amplifier A2 are smoothed by the smoothing circuit 9 and then applied to the gates of the transistors M1 and M2, so the transistor M1 operates as a constant current source.

According to the first embodiment, it is possible to configure a constant current source circuit that is not affected by variations in transistor characteristics and temperature fluctuations.

Note that since the amplifier A1 is used as an impedance converter, it is clear that a north follower or the like may be used instead of the amplifier. Further, since the resistor RL is used as a load of the current source transistor, it is clear that an active element such as a transistor may be used instead of the resistor RL.

FIG. 3 is a circuit diagram showing a second embodiment of the constant current source circuit according to the present invention, in which components having the same functions as those in FIG. 1 are given the same reference numerals. Fvls and Ma are N-channel MO8-FgT%Vi and Va are voltage sources, respectively.

The operation of the second embodiment described above can be more easily understood than the explanation of the operation of the previous embodiment, so a description thereof will be omitted.

According to this example, MOS-FETs Ms, M
A constant current source circuit that is not affected by variations in the characteristics of a and temperature fluctuations can be constructed.

FIG. 4 is a circuit diagram showing a third embodiment of the constant current source circuit according to the present invention, in which components having the same functions as those in FIG. 1 are given the same reference numerals. Tl and T2 are PNP transistors, respectively, and R1, ki, and s are resistors. Since the operation can be easily understood from the explanation of the operation of this implementation, the explanation will be omitted.
- According to the third embodiment, a constant current source circuit that is unaffected by variations in transistor characteristics and temperature fluctuations can be constructed.

FIG. 5 is a circuit diagram showing a fourth embodiment of the constant current source circuit according to the present invention, and parts having the same functions as those in FIGS. 1, 3, and 4 are designated with the same reference numerals. be. Ti and T◆ are each NPN! I) It is a transistor. The operation of this embodiment is also easier to understand than the explanation of the operation of the previous embodiment, so the explanation thereof will be omitted.

According to the fourth practical example, it is possible to configure a constant current source circuit that is not affected by variations in transistor characteristics and temperature fluctuations.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to configure a constant current source circuit that is free from current variations and fluctuations in the current source due to variations in transistor characteristics due to manufacturing variations in ICs and characteristic changes due to temperature fluctuations. Excellent except for technical shortcomings

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a first practical example of the present invention. FIG. 2 is an operation waveform diagram of FIG. 1, FIG. 3 is a circuit diagram showing a second embodiment of the invention, FIG. 4 is a circuit diagram showing a third embodiment of the invention, and FIG. 5 is a circuit diagram showing a third embodiment of the invention. A circuit diagram showing a fourth embodiment of the present invention, FIG. 6 is a circuit diagram explaining a conventionally known constant current source circuit, and FIG.
FIG. 3 is a static characteristic diagram of source voltage and drain current. 5... Current detection circuit, 6... Sample/hold circuit, 7... Reference voltage generation circuit, 8... Comparison circuit, 9
...Smoothing circuit, Ml, Ml...MOS-FgT,
A1. At...Amplifier, 81.32...Switch circuit. Easy 1 Ward 2 Concave Ichikasaki Question No. D 64 ≦ Name 7 Sen-1'FGs 1

Claims (1)

[Claims] 1. In a constant current source circuit that supplies a constant current from a power source to a load, each load has its source (emitter) side connected to the first power source and the drain (collector) side connected to the second power source. a plurality of first transistor groups connected to each other; and gates (bases) of these first transistor groups connected to sources (emitters).
a second transistor whose side is connected to a first power source; a first capacitor whose other end is connected to the drain (collector) side of the second transistor and whose other end is connected to the second power source;
A current detection circuit comprising a first switch circuit connected in parallel with the first capacitor and operated at a constant cycle; and a voltage across the first capacitor of the current detection circuit between the first switch circuit and the first switch circuit. A sample/hold circuit that performs sampling and holding operations synchronously and a constant voltage (
a reference voltage generation circuit that generates a reference voltage), a comparison circuit that compares the reference voltage of the reference voltage generation circuit and the output voltage of the sample-and-hold circuit; and after integrating the comparison result of the comparison circuit, this voltage is applied to the current 1. A constant current source circuit comprising: a smoothing circuit input to the gate (base) of a second transistor of the detection circuit.