JP3052818B2 - Constant current circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a constant current circuit,
In particular, the present invention relates to a constant current circuit suitable for MOS integration.

[0002]

2. Description of the Related Art As a conventional constant current circuit composed of MOS transistors of this type, for example, a first conventional constant current circuit having an operational amplifier in a voltage follower configuration, a current mirror circuit and a current mirror circuit are received. A second conventional constant current circuit of a self-bias type composed of two transistors and a resistor; and a third conventional general circuit in which a drain and a gate are connected in common and a resistance is loaded on the common connection drain / gate. A constant current circuit is known.

[0005] Referring to FIG. 5 showing a circuit diagram of a first conventional constant current circuit, the constant current circuit shown in FIG. R Gray et al., Translated by Minoru Nagata, analog integrated circuit design technology for VLSI, 2nd volume, Baifukan (1990), 310
An operational amplifier 1, a reference voltage circuit 2 for a voltage Vr connected to a positive input terminal of the operational amplifier 1, a drain of a positive power supply D, and a gate of an output terminal of the operational amplifier 1. And a resistor R having one end connected to the source of the transistor M101 and the inverting input end of the operational amplifier 1 and the other end connected to the negative power supply E, respectively.
1 and a reference voltage source 8 for supplying a potential difference, that is, a voltage V and a circuit operating current to the positive power supply D and the negative power supply E.

Referring to FIG. 5, the operation of the first conventional constant current circuit will be described. The operational amplifier 1 has a voltage follower configuration, and a reference voltage Vr from a reference voltage circuit 2 to a positive input terminal. Operates in such a manner that the potential Vr is also generated at the inverting input terminal in response to the supply of V. The gate and source of the transistor M101 are connected between the output terminal and the inverting input terminal of the operational amplifier 1, and the inverting input terminal is connected to the resistor R1.
Is grounded via As a result, even if the voltage V applied to the drain of the transistor M101 changes, the resistance R
Since a potential difference Vr is always generated at both ends of the transistor 1, a current of constant current I = (Vr / R1) continues to flow through the drain.

JP-A-5-191166 (Reference 2)
And R. Gregorian et al., Analog MO for signal processing
S Integrated Circuit, John Willy and Sons,
(R. Gregorian et al., Analo.
g MOS Integrated Circuits
for Signal Processing, Jo
hn Willy & Sons) 1986, 12th
Referring to FIG. 6 showing a circuit diagram of a second conventional constant current circuit described on page 7 (Reference 3) and the like, the constant current circuit shown in FIG. 6 is a current mirror circuit 3 including PMOS transistors M13 and M14. And transistors M13 and M14
NMOS transistors M11 each receiving the current of
M12, a resistor R1 connected between the source of the transistor M12 and the ground, and a startup circuit 4 for initial startup.
And a first constant current circuit and a common reference voltage source 8.

The operation of the second conventional constant current circuit will be described with reference to FIG. 6. Since this constant current circuit is a self-biased circuit, the operation is started by a start signal supplied from the start-up circuit 3. I do. Transistors M13 and M14 constituting current mirror circuit 3
Are equal in size and the transistor M1 receiving this current
1 and M12 are different in size, and the size of the transistor M12 having the source connected to the resistor R1 is increased. As a result, the resistance R1 has (V _GS1 −V _GS2 ) / R
One current I flows. Here, V _GS1 and V _GS2 are gate-source voltages of the transistors M11 and M12, respectively. The current I flows equally through the transistors M11 and M12 by the operation of the current mirror circuit 3. When the current I is obtained from these conditions, a constant current represented by the following equation (1) is finally obtained. I = (1 / R ² × k) × [(W / L) ₁ ^-1 / ² / (W / L) ₂ ^-1/2 ] ² (1) where k = μ × C _OX / 2 μ: electron mobility, C _OX :
The gate oxide film capacitance is shown.

FIG. 7 is a circuit diagram showing a third conventional constant current circuit. The constant current circuit shown in FIG. 7 includes a transistor M1 having a drain and a gate commonly connected and a source connected to a positive power supply D and a transistor M1 and a transistor M1. M1 common connection drain
A current control circuit 5 including a gate and a resistor R1 connected between the negative power supply E and a reference voltage source 8 common to the first constant current circuit.

The operation of the third conventional constant current circuit will be described with reference to FIG. 7. The operation between the source of the transistor M1 and the negative power supply of the resistor R1, that is, the positive power supply D and the negative power supply E
Assuming that the potential difference between the two is V, the current I =
A constant current of (V−V _GS ) / R1 flows.

FIG. 8A shows an example of a current variation characteristic with respect to a change in the resistance value of the second conventional constant current circuit analyzed by computer simulation, and FIG. 8A shows an example of a voltage-current characteristic of the third conventional constant current circuit. Each is shown in FIG.

[0010]

The above-described first conventional constant current circuit requires an operational amplifier and a reference voltage circuit, so that both the circuit scale and the occupied circuit area are large. Requires a constant current circuit, and the required voltage of the power supply for sufficiently operating the operational amplifier and the reference voltage circuit is high, so that the constant current region becomes narrow for a given power supply voltage. There were drawbacks.

Further, since the conventional second constant current circuit is a self-bias type circuit, there is a disadvantage that the operation of the circuit cannot be guaranteed unless a start trigger is supplied by an external start-up circuit or the like. Further, this constant current circuit can practically obtain only a small constant current value of about several tens nanoA to several microA, and this current value is proportional to 1 / R ² as shown in the equation (1). Therefore, there is a drawback that the range of variation of the current value with respect to the variation of the resistance value R is wider than that of other circuits proportional to 1 / R.

Furthermore, the conventional third constant current circuit has a drawback that it is not suitable for a constant current circuit requiring stability because the fluctuation of the power supply voltage directly changes the current value.

An object of the present invention is to eliminate the use of complicated circuits such as an operational amplifier circuit, a reference voltage circuit, and a start-up circuit, to increase the variation of the current value with respect to the variation of the resistance, and to set the voltage from a small voltage range. An object of the present invention is to provide a constant current circuit suitable for realizing a MOS integrated circuit which can generate a current and obtain a constant current in a wide voltage range.

[0014]

According to the present invention, there is provided a constant current circuit comprising:
A first resistor having one end connected to the second power source and a source connected to the first
And a first MOS transistor of a first conductivity type having a gate and a drain commonly connected to the power supply of the first type and connected to the other end of the first resistor. In a constant current circuit for holding current, when a power supply voltage which is a potential difference between the first and second power supplies is lower than a first voltage value, a voltage between a gate and a source of the first MOS transistor is increased. wherein a current sink circuit for stopping said sinking to sink operation to increase the drain current exceeds the first voltage value, the first when the power supply voltage exceeds a second voltage value M
A current source circuit for supplying a correction current to the first resistor so as to maintain the gate-source voltage of the OS transistor at a predetermined constant value.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Next, common components of the first embodiment and FIG. 7 of the present invention Referring to Figure 1, which shows the circuit diagram similarly are denoted by common characters, in FIG. The constant current circuit according to the present embodiment shown in FIG.
A current control circuit 5 including a MOS transistor M1 and a resistor R1, a current sink circuit 6 including NMOS transistors M2 and M3 and a resistor R2 and supplying a sink current to the current control circuit 1 at a low voltage; Current source circuit 7 comprising transistors M4, M5, resistors R3, R4, R5 and supplying a current at a high voltage, and a reference voltage source 8 supplying a reference voltage V which is a potential difference between positive power supply D and negative power supply E. And

The transistors M2 and M of the current sink circuit 6
3 is connected to a negative power supply E. The gate of the transistor M2 is connected to the drains of the transistors M1 and M3, and the drain is connected to the gate of the transistor M3 and the other end of the resistor R2 whose one end is connected to the positive power supply D.

In the power source circuit 7, the resistors R3, R4,
R5 is connected in series between the power supplies D and E, each source of the transistors M4 and M5 is connected to the positive power supply D, each gate is commonly connected, and further connected to a common connection point of the resistors R3 and R4. I have. As described above, the drain of the transistor M4 is commonly connected to the drain of the transistor M3 of the current sink circuit 6, and the drain of the transistor M5 is connected to the common connection point of the resistors R4 and R5.

Next, the operation of the present embodiment will be described with reference to FIG. 1. First, the reference voltage V supplied by the reference voltage source 8 is low, and the transistor M1 of the current control circuit 1 operates in the unsaturated region. In the region where the current is flowing, the gate-source voltage V _GS2 of the transistor M2 of the current sink circuit 6 is lower than the threshold voltage V _T2.
Is in the off state. Therefore, the gate voltage V _GS3 of the transistor M3 is applied with the voltage V of the positive power supply D via the resistor R2, and the transistor M3 is turned on. As a result, the gate-source voltage V of the transistor M1
_{Since GS1} increases and the drain current, that is, the reference current I increases, the reference current I can sufficiently flow even if the reference voltage V is low.

Next, when the reference voltage V increases, the gate-source voltage V _{GS2 of} the transistor M2 exceeds the threshold voltage V _T2 and turns on. Then, the gate potential of the transistor M3, which has been in the on state, falls from the voltage V to the threshold voltage V _T3 or less and turns off. As a result, as the voltage V increases, the operation of the current sink circuit 6 stops at a certain voltage.

[0020] Furthermore the voltage V increases, because the potential difference across the resistor R1 is increased, due to the potential difference increases in this
Necessary to flow a correction amount of the current I in the resistor R1 is generated. However, in the region of the voltage V at which the current sink circuit 6 stops, the current source circuit 7 starts to operate, and starts flowing current to the resistor R1 via the transistor M4. This current, that is, the correction current value can be set by selecting the area ratio of the transistors M4 and M5 and the values of the resistors R3, R4 and R5. By appropriately flowing the correction current corresponding to the increase in the voltage V from the transistor M4 to the resistor R1 by appropriate design, the drain current I of the transistor M1 can be kept constant.

Referring to FIGS. 2A and 2B, which show the voltage-current characteristics and the current fluctuation (hereinafter referred to as resistance fluctuation) characteristics with respect to the resistance fluctuation of the constant current circuit of the present embodiment analyzed by computer simulation, respectively. The analysis is performed assuming that the variation width of the resistance value shown in this figure is ± 20%, which is a general variation amount in an integrated circuit.
Compared with the resistance variation characteristics of the second conventional constant current circuit shown in FIGS. 2B and 8A, the variation of the resistance R1 is ±
While the variation of the current value in the circuit of the present embodiment is about ± 20% with respect to 20%, the variation of the current value of the second conventional constant current circuit is from −60% to −−20%. The fluctuation range is increased to about 30%. The reason is that the current value is proportional to 1 / R in the case of the circuit of the present embodiment, whereas it is proportional to 1 / R ² in the case of the second conventional constant current circuit as described above. .

Further, comparing the voltage-current characteristics of the third conventional constant current circuit shown in FIGS. 2A and 8B,
In the circuit of the present embodiment, the rise of the current value with respect to the application of the voltage V is faster than that of the third conventional constant current circuit due to the operation of the current sink circuit. Further, in the conventional circuit, the current value increases in proportion to the increase in the voltage V, but in the circuit of the present embodiment, the current is almost constant due to the operation of the current source circuit.

Next, a second embodiment of the present invention will be described with reference to FIG. 3, which is a circuit diagram also showing components common to those in FIG. This embodiment differs from the first embodiment in that a diode D1 is provided between the source of the transistor M5 and the positive power supply D instead of the current source circuit 7, and a diode D2 is provided between the drain and the negative power supply E. And a current source circuit 7A in which the resistors R3 to R5 are removed.

Referring to FIG. 4, which is a circuit diagram of a third embodiment of the present invention, in which components common to those of FIG. The difference from the first embodiment is that the sources of the transistors M5 and M4 are commonly connected instead of the current source circuit 7,
A current source circuit 7 in which a diode D1 is inserted between the source of the transistor M5 and the positive power source D, and a resistor R5 is inserted between the drain and the negative power source E, and the resistors R3 and R4 are deleted.
B.

The circuits of the second and third embodiments also have the same operating principle as the first embodiment, and can obtain a constant current.

[0026]

As described above, the constant current circuit according to the present invention has the first M circuit when the power supply voltage is lower than the first voltage value.
A current sink circuit that performs a sink operation to increase the drain current of the OS transistor and stops the sink operation when the power supply voltage exceeds the second voltage value, and a current sink circuit that stops the sink operation when the power supply voltage exceeds the second voltage value . Gate-source power
A current source circuit that supplies a correction current so as to maintain the voltage at a predetermined constant value, without using complicated circuits such as an operational amplifier, a reference voltage circuit, and an external start-up circuit. There is an effect that the current starts to flow from a low region and the amount of change in the current value with respect to the resistance change can be significantly suppressed.

[Brief description of the drawings]

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

FIG. 2 is a characteristic diagram showing an example of a voltage-current characteristic and an example of a resistance variation characteristic in the constant current circuit of the present embodiment.

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

FIG. 4 is a circuit diagram showing a constant current circuit according to a second embodiment of the present invention.

FIG. 5 is a circuit diagram showing an example of a conventional first constant current circuit.

FIG. 6 is a circuit diagram showing an example of a second conventional constant current circuit.

FIG. 7 is a circuit diagram showing an example of a third conventional constant current circuit.

FIG. 8 is a characteristic diagram illustrating an example of a voltage-current characteristic and an example of a resistance variation characteristic in a conventional constant current circuit.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 operational amplifier 2 reference voltage circuit 3 current mirror circuit 4 start-up circuit 5 current control circuit 6 current sink circuit 7, 7A, 7B current source circuit 8 reference voltage source M1 to M5, M11 to M14, M101 Transistors R1 to R5 Resistance D1, D2 diode

Claims (5)

(57) [Claims] A first resistor having one end connected to a second power source and a first conductive source having a source connected to the first power source, a gate and a drain connected in common, and connected to the other end of the first resistor; The first of the mold
And a constant current circuit that holds the drain current of the first MOS transistor at a predetermined constant current, wherein a power supply voltage, which is a potential difference between the first and second power supplies, is equal to the first power supply voltage.
A current sink that increases the gate-source voltage of the first MOS transistor to increase the drain current when the voltage is lower than the first voltage, and stops the sink operation when the voltage exceeds the first voltage. A first circuit when the power supply voltage exceeds a second voltage value;
A current source circuit for supplying a correction current to the first resistor so as to maintain a gate-source voltage of the MOS transistor at a predetermined constant value. 2. The method according to claim 2, wherein the current sink circuit has one end connected to the first terminal.
A second resistor connected to a power source of the second conductivity type, a source connected to the second power source, a gate connected to the gate of the first MOS transistor, and a drain connected to the other end of the second resistor. A second MOS transistor, a third MOS transistor of a second conductivity type having a source connected to the second power supply, a gate connected to a drain of the second MOS transistor, and a drain connected to a gate of the first MOS transistor, respectively. The constant current circuit according to claim 1, further comprising a transistor. 3. The method according to claim 2, wherein the current source circuit comprises the first and second current source circuits.
Second , third , and fourth resistors connected in series between the power supplies, a source connected to the first power supply and a drain connected to the first MOS.
A second MOS transistor of a first conductivity type having a gate connected to a common connection point of the second and third resistors, and a source connected to the first power source and a drain connected to the third and third transistors. A third conductive type third MO having a gate connected to a common connection point of the second and third resistors, respectively, is connected to a common connection point of the second and third resistors.
The constant current circuit according to claim 1, further comprising an S transistor. Wherein said current source circuit, a first dialog diode which connects the first electrode to the first power supply, a second dialog that the second electrode connected to said second power supply And a source connected to the first power supply and a drain connected to the first MOS.
A second MOS transistor of a first conductivity type having a gate connected to the first electrode of the second diode, and a source connected to the second electrode of the first diode; 2. The constant current circuit according to claim 1, further comprising a third MOS transistor of a first conductivity type, wherein a drain of the gate of the second MOS transistor is connected to a first electrode of the second diode. . 5. A current source circuit comprising: a diode having a first electrode connected to the first power supply; a second resistor having one end connected to the second power supply; Gate to the second electrode
Wherein a first conductivity type second MOS transistor of which drain to the other end of the second resistor connected to the gates of the first MOS transistor, a gate of the source to the second electrode before Kida diode first
The drain of the second MOS transistor is connected to the second
2. A constant current circuit according to claim 1, further comprising a third MOS transistor of a first conductivity type connected to the other end of said resistor.