JPH07121255A - Constant current source circuit - Google Patents

Abstract

PURPOSE:To enable the constant-current source circuit to actuate itself automatically and stably without making any consumable current to an actuating circuit itself. CONSTITUTION:In the silicon band gap type constant-current source circuit consisting of two current mirror circuits M1 and M2 and a resistance R1 which determines the current gains of those current mirror circuits, plural diode- connected transistors(TR) T5-T9 are connected in series between the output node N1 and low power source potential VSS of the circuit. The threshold value of the whole series-connected circuit is set higher than the voltage at the node N1 in a normal state, and consequently this series-connected circuit turns OFF in the normal state to have no current consumption and turns ON only at the time of actuation after the source voltage drops, so that the circuit can be actuated again.

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 circuit for starting a constant current source circuit in a CMOS integrated circuit by self-excitation.

[0002]

2. Description of the Related Art A CMO is an example of a conventional constant current source circuit.
There is a circuit that uses the S structure to generate a constant current by utilizing the bandgap of silicon. FIG. 2 shows an example of the circuit.

The circuit of FIG. 2 basically comprises two current mirror circuits M1 and M2 and a resistor R1 which determines the current gain of these current mirror circuits.

The current mirror circuit M1 comprises a diode-structured NMOS (N-channel MOS) transistor T2 having a gate and a drain connected to each other, and an NMOS transistor T1 having the gate and the gate of the transistor T2 commonly connected to each other. Then, a current I3 corresponding to the drain current I2 of the transistor T2 supplied to the node N2
Becomes the drain current of the transistor T1, and the node N1
Is supplied to.

The relationship between the currents I2 and I3 is determined by the current gain of the current mirror circuit M1 and is determined by the resistor R1.

The current mirror circuit M2 comprises a diode-structured PMOS (P-channel MOS) transistor T3 having a gate and a drain connected to each other, and a PMOS transistor T4 having a gate commonly connected to the gate of the transistor T3. Then, a current I corresponding to the drain current I1 of the transistor T3 supplied to the node N1
2 becomes the drain current of the transistor T4, and the node N
2 is supplied.

Further, a PMOS transistor T11 having a gate connected to the node N1 is provided, and the transistor T11 and the transistor T3 constitute a current mirror circuit for deriving an output. The drain current I0 of the transistor T11 is used as the output current, but in the present example, the load NMOS transistor T
This output current I0 is derived using 10.

A starting NMOS transistor T12 is provided between the node N1 and the reference low potential VSS, and a starting reset signal is applied to the gate of the transistor T12.

It is assumed that all the transistors are enhancement type.

When activating such a circuit, the reference high potential V
The DD is supplied and the activation signal is supplied to the gate of the transistor T12. Then, the NMOS transistors T1 and T2 and the PMOS transistors T3 and T4 are turned on, and the current gain of the current mirror circuit M2 and the resistance R
It becomes stable at the operating point where the product of the current gain of the current mirror circuit M1 determined by 1 becomes 1.

In this stable state, the current flowing in the closed loop circuit composed of both current mirror circuits M1 and M2 and the resistor R1 is taken out as a constant current I0 by the current mirror circuit using the transistor T11.

In this circuit, it is necessary to detect the power-on at the time of start-up and use the start-up signal as the gate input of the transistor T12. Also, when the power supply fluctuates, all of the transistors T1 to T4 are all affected by a sudden drop in the power supply voltage. It becomes a cutoff and becomes stable, and the constant current I0 cannot be generated.

Therefore, a constant current source circuit to which a self-excited starter circuit is added is disclosed in Japanese Patent Laid-Open No. 4-111008, and its configuration is shown in FIG. 3, the same parts as those in FIG. 2 are designated by the same reference numerals.

In FIG. 3, the circuit of FIG. 2 is provided with an NMOS transistor T13 and a PMOS transistor T14 for supplying an off-leak current, nodes N2 and N1 and a power source VS.
They are provided between S and VDD, respectively, and the self-excitation operation is performed by supplying the off-leakage currents of the transistors T13 and T14 to the nodes N2 and N1 at the time of start-up or at the time of self-starting after the power supply is lowered after the start-up. I am supposed to do it. The details of the operation are shown in the above-mentioned publication.

[0015]

In the self-excited constant current source circuit shown in FIG. 3, the off-leakage occurs in the input / output nodes N1 and N2 of the current mirror circuits M1 and M2 through the transistors T13 and T14 which are always off. Since it is a method of supplying current, the off-leakage current always flows in the circuit even when the circuit is in a steady state, and in addition to the problem of increased power consumption, it is necessary to design the circuit considering this off-leakage current. It has the drawback of being difficult to design.

An object of the present invention is to provide a constant current source circuit in which a self-exciting current is supplied only at the time of starting and no current flows in the self-exciting circuit in a steady state.

[0017]

According to the present invention, first and second nodes, and a first current at the first node,
A first current mirror circuit that supplies a second current corresponding to the current gain to the second node, and a second current to the second node and a current gain to the first node. A constant current source circuit including a second current mirror circuit for respectively supplying a third current, and a resistance element that determines a current gain of the second current mirror circuit,
A constant current source circuit is obtained which has a switching circuit having a threshold value larger than the voltage of the first node at the time of normal operation, between the node and the reference potential point.

[0018]

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

FIG. 1 is a circuit diagram of an embodiment of the present invention, and the same parts as those in FIG. 2 are designated by the same reference numerals. To describe the part different from FIG. 2, in this example, an NMOS with a diode connection configuration is provided between the node N1 and the reference low power supply potential VSS.
It has a configuration in which a plurality of transistors T5 to T9 are connected in series, and the other configuration is the same as that of FIG. 2 and its description is omitted.

Here, the high power supply potential VDD is 5V and the low power supply potential VSS is 0V. In this circuit, the product of the current gains generated in the two current mirror circuits M1 and M2 becomes 1 and the stable state is achieved, as in the conventional example.

The value of the current I1 at the node N1 is determined by the gate width W of each of the transistors T1 and T2 and the transistors T3 and T4, the gate length L, and the value of the resistor R1. Voltage VN1
Is a voltage between 5V and 0V.

The voltage VN2 at the node N2 changes to the threshold value V of the transistor T2 when the power is turned on or the power supply voltage suddenly drops.
When it becomes lower than T2 and the voltage VN1 of the node N1 becomes lower than the threshold VT3 of the transistor T3, these transistors are cut off and the currents I1 and I2 stop flowing.

However, when the voltage VN1 of the node N1 tries to approach the power supply voltage VDD due to the cut-off state and exceeds the sum VT0 of the threshold values of the transistors T5 to T9 as diode-connected switching circuits, this switching circuit (transistor T5 ~ T9 series circuit)
Is turned on, and the voltage VN1 of the node N1 causes a voltage drop.

Current mirror circuits M1 and M2 and resistor R
In the closed loop circuit composed of 1, the voltage drop of the node N1 causes I1 to start flowing in the current of the node N1 and is stable in a state where the product of the current gains of the two current mirror circuits M1 and M2, which is the feedback circuit, is 1. It returns to the state.

Diode-connected transistor T5
The number of serially connected stages of T9 is set so that the sum VT0 of the thresholds of these transistors becomes higher than the voltage VN1 of the node N1 in the stable state. This is because the diode-connected transistors T5 to T9 are cut off during the stable operation of the constant current source circuit.

[0026]

As described above, according to the present invention, a switching circuit which is completely in an off state in a steady state and is turned on only at the time of starting is added to be a self-excited type, so that a stable constant current can be obtained. At the same time, there is an effect that a steady current does not flow in the self-excited circuit.

[Brief description of drawings]

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

FIG. 2 is a circuit diagram showing an example of a conventional constant current source circuit.

FIG. 3 is a circuit diagram showing another example of a conventional constant current source circuit.

[Explanation of symbols]

 M1 and M2 current mirror circuit T1 to T4 current mirror transistor T5 to T9 diode configuration transistor T10 load transistor T11 constant current deriving transistor N1 and N2 node R1 resistance element

Claims (2)

[Claims] 1. A first current mirror for supplying first and second nodes, and a first current to the first node and a second current to the second node according to a current gain, respectively. A circuit, the second current to the second node, the first current
A constant current source circuit including a second current mirror circuit for respectively supplying a third current according to a current gain to the node of, and a resistance element for determining a current gain of the second current mirror circuit, Between the first node and the reference potential point,
A constant current source circuit having a switching circuit having a threshold value higher than the voltage of the first node during normal operation. 2. The constant current source circuit according to claim 1, wherein the switching circuit has a plurality of diode-connected transistor elements connected in series.