JPH08228114A - Constant current source circuit - Google Patents

Abstract

PURPOSE: To improve the yield of manufacture by suppressing the fluctuation in an output current caused by the manufacture dispersion of components, especially, of a resistor in the constant current source circuit. CONSTITUTION: This circuit is composed of a first current mirror circuit composed of P transistors 1, 5, 6 and 8, second current mirror circuit composed of N transistors 2, 7 and 8, conversion circuit 70 and variable resistor means 71. The conversion circuit 70 defines the other terminal of a drain resistor 52 to connect the drain of an N transistor 4 as an input/output terminal for outputting a voltage for which the output current of the first current mirror circuit is inputted and converted. The variable resistor means 71 is composed of two fixed resistors 50 and 51 serially connected between two terminals and an N transistor 3 for which the drain is connected to the junction of these two fixed resistors and the source is connected to one of two terminals.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a constant current source circuit, and more particularly to a constant current source circuit composed of a current mirror circuit.

[0002]

2. Description of the Related Art Conventionally, a constant current source circuit of this type has been used as a constituent element of a circuit such as a constant current source for bias, a constant current load, and distribution of current ratio. For example, FIG. 4 is a circuit diagram showing an example of a conventional constant current source circuit.

Referring to FIG. 4, when the circuit configuration is roughly divided, this constant current source circuit is composed of P-type transistors 1 and 6.
And 9, a first current mirror circuit, a second current mirror circuit including N-type transistors 2, 7 and 8, and a source resistor 55.

In the first current mirror circuit, the gates of P-type transistors 1, 6 and 9 are both connected to an input terminal, the drain of P-type transistor 1 is used as an input terminal, and the drains of other P-type transistors are used as output terminals, respectively. There is. Among them, the drain of the P-type transistor 9 is led to the ejection current output terminal 60.

In the second current mirror circuit, the gates of N-type transistors 2, 7 and 8 are both connected to the input terminal, the drain of the N-type transistor 7 is used as the input terminal, and the drains of the other N-type transistors are used as the output terminals, respectively. There is. Among them, the drain of the N-type transistor 8 is led to the current output terminal 61 for suction. Further, the output current and the input current of the first current mirror circuit are input or output to the input terminal and the output terminal of the second current mirror circuit, respectively, to form a positive feedback loop of the input / output current.

The source resistor 55 has one end connected to the source of the N-type transistor 2 of the second current mirror circuit that outputs the input current of the first current mirror circuit, and the output current of the N-type transistor 2 is negatively fed back. The output current value is set by the operation.

Next, the output current of this constant current source circuit is obtained. The gate widths of the transistors 1, 2, 6, 7, 8 and 9 are W1, W2, W6, W7, W8 and W9 respectively, the gate lengths are L1, L2, L6, L7, L8 and L9 respectively, and the source resistance 55 Let R be the value of. Also, the transistor sizes are defined as W1 / L1 = W6 / L6 = W9 / L9 and W7 / L7 = W8 / L8.

When each transistor is operated in the strong inversion region, the output current Iout flowing through the terminals 60 and 61 is

[0009]

This circuit exhibits good constant current characteristics with respect to fluctuations in the power supply voltage.

Another known example is shown in FIG.
Is a circuit diagram of a constant current source circuit disclosed in Japanese Patent Laid-Open No. 61-145616.

The structure of the circuit shown in FIG. 5 will be described in block units. This constant current source circuit includes a transistor 2
0, the diode 30, and the resistors 56 and 57, the starting circuit 70, the transistors 21, 22 and 23, the diodes 31 and 32, and the resistor 58, the constant current circuit 71, the transistors 24 and 25, and the operational amplifier circuit 40.
And a temperature characteristic canceling circuit 72 including a resistor 59.

Next, the operation of this circuit will be described.
First, when power is supplied, current flows in the collector of the transistor 20 and the constant current circuit 71 is activated.

On the other hand, in the temperature characteristic canceling circuit 72, the terminal voltage of the resistor 59 becomes equal to the voltage generated at the terminal of the diode 32 due to the feedback loop composed of the operational amplifier circuit 40, the transistor 24 and the resistor 59, and this voltage is applied to the resistor. A current having a magnitude divided by the value of 59 flows through the transistor 24.

As a result, the transistor 23 of the constant current circuit 71 is connected to the discharge current output terminal 60 of the constant current source circuit.
And a mirror current from the transistor 25 of the temperature characteristic canceling circuit 72 is added, and a current flows. At this time, by appropriately setting the resistance values of the resistors 58 and 59 and the emitter area ratios of the transistors 24 and 25, it is possible to cancel the fluctuation current component due to the temperature change, and the constant current source circuit discharge current output. The constant current discharged from the terminal 60 can be constant with respect to the temperature change.

[0016]

In the conventional constant current source circuit shown in FIG. 4, as can be seen from the expression of Iout, the resistance value of the source resistor 55 fluctuates greatly.
Therefore, for example, when it is used as a bias circuit of an operational amplifier circuit, there is a problem in that the characteristics of the operational amplifier circuit cause a large manufacturing variation and the manufacturing yield is reduced.

Further, the conventional constant current source circuit shown in FIG.
It has a good temperature characteristic of output current. However, the fluctuation of the output current due to the variation of the absolute values of the resistors 58 and 59 is shown in FIG.
As is the case with the circuit shown in FIG. 3, there is a problem in that the use of the operational amplifier 40 necessitates a countermeasure against frequency stability and increases the number of elements.

Therefore, it is an object of the present invention to suppress fluctuations in output current due to manufacturing variations of constituent elements, particularly resistors, in a constant current source circuit to improve the manufacturing yield.

[0019]

Therefore, in the constant current source circuit according to the present invention, one drain of a plurality of transistors whose gates are connected to the input terminal is used as the input terminal, and the other drains are used as the output terminals, respectively. Current mirror circuit, a second current mirror circuit of complementary polarity that inputs or outputs the output current and the input current of the first current mirror circuit, and outputs the input current of the first or second current mirror circuit. A constant current source circuit having a source resistance whose one end is connected to the source of the transistor
Alternatively, a conversion circuit for converting the output current of the current mirror circuit of No. 2 into a voltage is provided, and the source resistance includes variable resistance means whose resistance value is controlled by the conversion voltage of the conversion circuit.

[0020]

Next, the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram showing a first embodiment of the constant current source circuit of the present invention. Referring to FIG. 1, if the circuit configuration is roughly divided, the constant current source circuit of the present embodiment has a first current mirror circuit composed of P-type transistors 1, 5, 6 and 9 and an N-type transistor 2, 7. 2nd consisting of 8 and
Current mirror circuit, conversion circuit 70, and variable resistance means 7
1 and 1.

The first current mirror circuit connects the gates of P-type transistors 1, 5, 6 and 9 together to the input terminal,
The drain of the P-type transistor 1 is used as an input terminal, and the drains of the other P-type transistors are used as output terminals.
Among them, the drain of the P-type transistor 9 is led to the ejection current output terminal 60.

In the second current mirror circuit, the gates of N-type transistors 2, 7 and 8 are both connected to the input terminal, the drain of the N-type transistor 7 is used as the input terminal, and the drains of the other N-type transistors are used as the output terminals, respectively. There is. Among them, the drain of the N-type transistor 8 is led to the current output terminal 61 for suction. Further, the output current and the input current of the first current mirror circuit are input or output to the input terminal and the output terminal of the second current mirror circuit, respectively, to form a positive feedback loop of the input / output current.

The conversion circuit 70 is composed of an N-type transistor 4 having a source grounded and a gate connected to a drain, and a drain resistor 52. The other end of the drain resistor 52 that connects the drain of the N-type transistor 4 is used as an input / output terminal that inputs the output current of the first current mirror circuit and outputs a converted voltage.

The variable resistance means 71 has two fixed resistors 50 and 51 connected in series between two terminals, a drain connected to an intermediate connection point between these two fixed resistors, and a source connected to one of the two terminals. And an N-type transistor 3. Further, the gate of the N-type transistor 3 is connected to the input / output terminal of the conversion circuit 70 to control the resistance value between the two terminals. By connecting one of the two terminals to the source of the N-type transistor 2 and grounding the other terminal, the output current value is set by the negative feedback operation of the output current itself of the N-type transistor 2.

Next, the operation of the constant current source circuit of this embodiment will be described with reference to FIG.

When the constant current source circuit of this embodiment is supplied with power, the input and output currents of the first and second current mirror circuits of the positive feedback loop composed of the P-type transistors 1 and 6 and the N-type transistors 2 and 7, respectively. Is activated by leakage current. The output current of the activated N-type transistor 2 reaches a steady state at the current value set by the resistance value of the variable resistance means 71 due to the negative feedback operation of the output current itself by the resistance value of the variable resistance means 71.

At this time, the current supplied by the P-type transistor 5 is converted into a voltage by the N-type transistor 4 which is diode-connected to the drain resistor 52. This converted voltage is input to the gate of the N-type transistor 3. Here, when the drain voltage is set to be sufficiently low, the N-type transistor 3 operates in the triode region and controls the resistance value between the drain and the source by the gate potential. After all, the resistance value of the variable resistance means 71 as the source resistance of the N-type transistor 2 depends on the current flowing through the drain of the N-type transistor 2 itself.

It is now assumed that the resistors 50 and 51 and the drain resistor 52 have a resistance value larger than the designed value due to manufacturing variations. At this time, the current flowing through the drain resistance 52 decreases, but the resistance value of the drain resistance 52 itself increases. Therefore, the fluctuation of the converted voltage output to the input / output terminal of the conversion circuit 70 is canceled out and a slight fluctuation occurs. stay. N-type transistor 3 which inputs this converted voltage to the gate
The resistance value between the drain and the source of the device also changes only slightly.

The variable resistance means 71 increases the resistance value as a whole by the fluctuation of the resistance values of the resistors 50 and 51. However, since the N-type transistor 3 in which the gate voltage fluctuation is only a slight fluctuation is connected in parallel with the resistor 51, the fluctuation of the combined resistance value of the entire variable resistance means 71 is suppressed to be small.

Therefore, according to the constant current source circuit of this embodiment,
It is possible to suppress the fluctuation of the output current due to the manufacturing variation of the absolute resistance value.

In the conversion circuit 70, the N-type transistor 4 having the source grounded and the gate connected to the drain is connected in series with the drain resistor 52.
The converted voltage output including the threshold value variation of 1 can offset the threshold variation of the N-type transistor 3, and the variation of the output current due to the manufacturing variation of the threshold value of the N-type transistor 3 can be suppressed to be small.

A circuit simulation was carried out to examine the above situation. FIG. 2 is a characteristic diagram showing a circuit simulation result of the constant current source circuit of this embodiment. This characteristic diagram shows that the temperature coefficient of the resistance + 0.16% / K and the design value of the output current of 20 μA are the conditions for the circuit simulation, the absolute accuracy of the resistance is -10 to + 25% as the parameter variable, and the temperature range is -30 to 85 ° C. Shows the characteristics of the output current at. For comparison, the output current characteristics of the constant current source circuit of this embodiment shown in FIG. 1 and the conventional constant current source circuit shown in FIG. 4 are also shown.

As shown in FIG. 2, the variation of the output current with respect to the fluctuation of the absolute accuracy of the resistance at room temperature (27 ° C.) is −29 to + 19% in the conventional constant current source circuit, whereas in the present embodiment. In the example constant current source circuit, -20 to +12
%, Which is a significant improvement. Further, the constant current source circuit according to the present embodiment and the conventional constant current source circuit cancel out the characteristic of the resistance having the positive temperature coefficient and the surface mobility of the MOS transistor having the negative temperature coefficient to each other, so that a good output current can be obtained as a whole. It shows the temperature characteristics. However, by further comparing the two, the temperature coefficient of the output current when the resistance value is the design center value is +2.0 μA / 100 ° C. in the conventional constant current source circuit, whereas the temperature coefficient of the present embodiment is constant. + 1.1μA / 10 in current source circuit
It was 0 ° C, which is also improved.

The reason for these improvements is that the conversion circuit 70 and the variable resistance means 71 are provided, and the conversion voltage of the conversion circuit 70 is suppressed to a slight fluctuation with respect to the absolute value fluctuation of the resistance, and this conversion voltage is input to the gate. This is because the variation rate of the combined resistance of the variable resistance means 71 including the MOS transistor and the resistance element can be suppressed to be small.

FIG. 3 is a circuit diagram showing a second embodiment of the constant current source circuit of the present invention.

Referring to FIG. 3, the constant current source circuit of the present embodiment is a diode-connected N-type transistor 10, 1.
The starting time of the constant current source circuit is shortened by adding a starting circuit composed of 1, 12 and 13 and resistors 53 and 54 to the first embodiment shown in FIG. When the current reaches a steady state, a voltage drop occurs across the resistor 54, so that the N-type transistor 13 becomes non-conductive and the starting circuit is disconnected from the constant current source circuit.

Therefore, the constant current source circuit of this embodiment operates in the steady state in the same manner as the first embodiment shown in FIG.

[0039]

As described above, the constant current source circuit according to the present invention includes the conversion circuit and the variable resistance means, and suppresses the conversion voltage of the conversion circuit to a slight fluctuation with respect to the fluctuation of the absolute value of the resistance. , MO to input this converted voltage to the gate
Since the variation rate of the combined resistance of the variable resistance means including the S transistor and the resistance can be suppressed to be small, the variation of the output current due to the manufacturing variation of the resistance value can be suppressed to be small, and the manufacturing yield is improved.

For the same reason, the temperature coefficient of the output current can be suppressed to a small value.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a first embodiment of a constant current source circuit of the present invention.

FIG. 2 is a characteristic diagram showing a circuit simulation result of the constant current source circuit of FIG.

FIG. 3 is a circuit diagram showing a second embodiment of the constant current source circuit of the present invention.

FIG. 4 is a circuit diagram showing an example of a conventional constant current source circuit.

FIG. 5 is a circuit diagram showing another example of a conventional constant current source circuit.

[Explanation of symbols]

1, 5, 6, 9 P-type transistor 2, 3, 4, 7, 8, 10, 10, 11, 12, 13 N-type transistor 20, 21, 22, 23, 24, 25 Bipolar transistor 40 Operational amplifier 50, 51, 52, 53, 54, 55, 56, 57, 5
8,59 Resistance 60 Discharge current output terminal 61 Suction current output terminal 70 Conversion circuit 71 Variable resistance means

Claims (2)

[Claims] 1. A first current mirror circuit in which one drain of a plurality of transistors whose gates are connected to an input terminal is used as the input terminal and other drains are used as output terminals, respectively, and an output of the first current mirror circuit. A second current mirror circuit of complementary polarity for inputting or outputting a current and an input current, respectively, and a source resistance having one end connected to the source of the transistor for outputting the input current of the first or second current mirror circuit. In the current source circuit, a conversion circuit for converting the output current of the first or second current mirror circuit into a voltage is provided, and the source resistance comprises variable resistance means whose resistance value is controlled by the conversion voltage of the conversion circuit. Constant current source circuit characterized by. 2. The conversion circuit has an input / output terminal for inputting an output current of the first or second current mirror circuit and outputting a converted voltage, and a source having the same polarity as a transistor connected to the source resistor, The variable resistance means includes a first transistor grounded or connected to a power source, and a drain resistance having a drain and a gate of the first transistor commonly connected to one end and the other end connected to the input / output terminal.
Two fixed resistors connected in series between terminals and a drain connected to the connection point of the two fixed resistors having the same polarity as the first transistor and a gate connected to the input / output terminal, The constant current source circuit according to claim 1, further comprising a second transistor whose source is connected to the second transistor.