JPH0973332A - Constant current supply device - Google Patents

Abstract

(57) Abstract: The temperature dependence of the output current of a current mirror circuit is reduced or eliminated. Kind Code: A1 Current mirror circuits 2, 3, reference current sources 4, 17, 18 connected to the current mirror circuits, and a thermal coupling element 11 arranged in the vicinity of the current mirror circuits for sensing ambient temperature. And the ambient temperature is sensed by the thermal coupling element 11 and fed back to the reference current source to reduce or eliminate the temperature dependency of the output current of the current mirror circuit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a constant current supply device, and more particularly to a constant current supply device having a temperature compensation function.

[0002]

2. Description of the Related Art FIG. 16 is a circuit diagram showing a conventionally known current mirror circuit. In FIG. 16, 1 is a reference current source and 4 is a voltage source (Vcc). 2 and 3 are PMOS transistors forming a current mirror circuit,
The reference current source 1 is connected to the drain gate short end of the PMOS transistor 2, and the drain current value is PM.
It is mirrored by the output current of the OS transistor 3. 5 is G
This is the ND (ground) potential point.

FIG. 17 is a circuit diagram showing a cathode common type laser drive circuit disclosed in Japanese Patent Laid-Open No. 5-243654. In FIG. 17, reference numeral 1 is a reference current source for determining the drive current of the laser diode 9. Normally, the light emission amount of the laser diode 9 is monitored by a photodiode (not shown) so that the output current becomes constant. Controlled by. PMOS forming a current mirror circuit
The operations of the transistors 2 and 3 are the same as those shown in FIG. The drain output of the PMOS transistor 3 is N
It is mirrored at the collector base short end of the PN transistor 6. The base of the NPN transistor 7 is connected to the collector base short end of the NPN transistor 6, and these NPN transistors 6 and 7 form a current mirror circuit. Here, by setting the emitter area ratio of the NPN transistors 6 and 7 to 1: N,
A current (1 + N) times the drain output current of the PMOS transistor 3 can be output from the common emitter end. 9 is a laser diode, the cathode of which is GND (ground)
It is connected to the potential point 5 and the anode is connected to the common emitter end of the NPN transistors 6 and 7. The N-channel MOS transistor 8 is a switching transistor, which is turned on when the control signal input terminal 10 is at the HI level, absorbs the current output of the PMOS transistor 3, and does not flow into the collector-base short end of the NPN transistor 6, The current mirror circuit composed of NPN transistors 6 and 7 is turned off, and the laser drive current is 0.
Becomes The NMOS transistor 8 is turned off when the control signal input terminal 10 is at the LOW level, the current output of the PMOS transistor 3 is multiplied by (1 + N) by the current mirror circuit composed of the NPN transistors 6 and 7, and the laser diode 9 is turned on. To drive.

[0004]

However, FIG.
In the conventional example of the current mirror circuit shown in, since the current mirror circuit itself is also a heat source, the ambient temperature changes at the beginning and end of the current flow, and the PMOS transistors 2 and 3
There is a problem that the threshold voltage V _{TH of the above} is interlocked and the output current has temperature dependency.

Further, in the conventional example of the cathode common type laser drive circuit shown in FIG. 17, since the NPN current mirror circuit itself is a heat source in addition to the PMOS current mirror circuit, the ambient temperature changes and the PMOS In addition to the threshold voltage V _TH of the transistors 2 and 3, the base-emitter voltage V _{BE of} the NPN transistors 6 and 7 fluctuates, and there is a problem that the laser drive current has temperature dependence.
Therefore, when a black-colored original is printed by a laser beam printer using the laser drive circuit, there is a problem that a difference occurs in the ambient temperature of the laser drive circuit at the beginning and the end, resulting in a density difference in an image.

Therefore, in view of the above points, an object of the present invention is to reduce or eliminate the temperature dependence of the output current of the current mirror circuit.

[0007]

To achieve the above object, a constant current supply device of the present invention includes a current mirror circuit, a reference current source connected to the current mirror circuit, and a vicinity of the current mirror circuit. And a thermal coupling element for sensing the ambient temperature, the ambient temperature is sensed by the thermal coupling element and fed back to the reference current source to determine the temperature dependence of the output current of the current mirror circuit. Characterized by being small or eliminated.

The constant current supply device of the present invention is a constant current supply device in which a plurality of stages of current mirror circuits are provided, and the output current of the current mirror circuit of the preceding stage is the reference current of the current mirror circuit of the following stage. A thermal coupling element is arranged in the vicinity of at least one current mirror circuit of a plurality of current mirror circuits, the ambient temperature is sensed by the thermal coupling element, and a current mirror circuit in the vicinity of the thermal coupling element is provided. By feeding back to the supplied reference current, the temperature dependence of the output current of the current mirror circuit is reduced or eliminated.

Further, in the constant current supply apparatus of the present invention, in the constant current supply apparatus of the present invention, the thermal coupling element and at least a part or all of the current mirror circuit are covered with a common wiring layer. It is characterized by having done.

In the present invention, the thermal coupling element is arranged in the vicinity of a part or the whole of the current mirror circuit (preferably a large heat generation region). For example, when the current mirror circuit is composed of two bipolar type transistors, the thermal coupling element is arranged in the vicinity of one or two bipolar transistors, or the collector and emitter of one or two bipolar transistors, It can be arranged in the vicinity of a part (one or more) or all of the base, wiring and the like. When a plurality of current mirror circuits are provided, the thermal coupling element can be further arranged near the plurality of current mirror circuits.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION

(Operation) According to the present invention, the temperature dependence of the output current of the current mirror circuit can be reduced or eliminated. Further, when the semiconductor laser is driven by the output current of the current mirror circuit, the temperature dependence of the laser drive current can be reduced or eliminated, and in the laser beam printer in which the laser drive current is determined, the image density is uniform. Can be realized.

Further, if the thermal coupling element and a part or all of the current mirror circuit are covered with a common wiring layer, the high thermal conductivity of the wiring layer can be utilized to surround the thermal coupling element. It is possible to improve the temperature sensing characteristics.

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

(First Embodiment) FIG. 1 shows a first embodiment of the present invention.
2 is a circuit configuration diagram showing an embodiment of FIG. In the figure, 1
2 to 15 are resistance groups connected in series, and both ends of the resistance group are connected to a GND (ground) point 5 and a power supply (Vcc) 4. 11 is a PNP transistor for thermal coupling,
It is connected in parallel with the resistors 13 and 14. 16 and 1
A buffer circuit 7 buffers the common contact potential Vcont of the resistors 13 and 14. Reference numeral 18 is a reference current (Iref) setting resistor. 2 and 3 are P constituting a current mirror circuit
It is a MOS transistor, and the NPN transistor 17 is provided at the drain gate short end of the PMOS transistor 2.
Connected to the collector of the
It is mirrored by the output current of the transistor 3. Here, the reference current source is the power supply 4, the NPN transistor 17, the resistor 18
It is.

Next, Vcont in the above configuration is expressed by the following equation.

[0016]

[Equation 1] (However, VBE: base-emitter voltage of the thermal coupling PNP transistor 11) By disposing the thermal coupling PNP transistor 11 in the vicinity of the current mirror circuit configured by the PMOS transistors 2 and 3, Vcont is set to the temperature shown below. It has characteristics.

[0017]

[Equation 2] From the equation (2), the reference current (Iref) has the following temperature characteristics.

[0018]

(Equation 3) However, it is assumed that ∂RC / ∂T = 0 by arranging the reference current setting resistor 18 in a place where the temperature change is small.

The value of the equation (3) is used as the PMOS transistor 2
The temperature dependence of the output current can be reduced or eliminated by setting the temperature characteristics of the output current of the PMOS current mirror circuit configured by 3 and 3 to the same value with different polarities.

Further, a PNP current mirror circuit may be used instead of the PMOS current mirror circuit used in FIG. 1, or an NPN transistor, a PMOS transistor, instead of a PNP transistor may be used as a thermal coupling element.
It is also possible to use NMOS transistors, resistors and the like. (Second Embodiment) FIG. 2 is a circuit configuration diagram showing a second embodiment of the present invention. In the present embodiment, the first shown in FIG.
The output current of the PMOS current mirror circuit of the embodiment is N
It is the reference current of the current mirror circuit composed of the PN transistors 6 and 7. The NPN transistor 6,
By setting the emitter area of 7 to 1: N, the output current of the PMOS current mirror circuit is (1+
N) times the output current is obtained.

When N is large, a large current flows through the NPN transistor 7 as compared with other transistors, and the temperature change is large, so it is preferable to dispose a thermal coupling element in the vicinity thereof. (Third Embodiment) FIG. 3 is a modification of the first embodiment shown in FIG. In FIG. 1, a PNP is used as a thermal coupling element.
Instead of using transistors, in FIG.
The S transistor 19 is used. In Figure 1, PMOS
Although the current mirror circuit composed of transistors is used, in FIG. 3, the current mirror circuit composed of NPN transistors 21 and 22 is used. In addition, NPN in FIG.
Instead of the transistor 17, a PNP transistor 20 is used in FIG. The NMOS transistor 19 is arranged near the current mirror circuit formed by the NPN transistors 21 and 22.

The temperature characteristics of the reference current (Iref) in the above structure are shown below.

[0023]

(Equation 4) (However, VGS: gate-source voltage of thermal coupling PMOS transistor 19) (Fourth Embodiment) FIG. 4 is a modification of the second embodiment shown in FIG. In FIG. 4, the main changes other than the elements (PNP transistors) with the subscripts 23 and 24 are shown in FIG.
Since it has been described above, it will be omitted. Instead of using the current mirror circuit composed of NPN transistors 6 and 7 in FIG. 2, PNP transistors 23 and 24 are used in FIG. (Fifth Embodiment) FIGS. 5 and 6 are views showing an embodiment in which the output currents of the circuits shown in FIGS. 1 and 2 drive a laser diode 9 of a common cathode type. That is, the anode end of the laser diode 9 is connected to the output end of the current mirror circuit, and the cathode end is grounded (G
ND) connected to point 5. (Sixth Embodiment) FIGS. 7 and 8 show an embodiment in which the output current of the circuits shown in FIGS. 3 and 4 drives a laser diode 9 of common anode type. That is, the cathode end of the laser diode 9 is connected to the output end of the current mirror circuit, and the anode end is connected to the power supply (Vcc) point 4. (Seventh Embodiment) FIG. 9 is a plan view showing a seventh embodiment of the present invention. In the figure, subscripts 2, 3, 6,
The elements labeled with 7 and 11 correspond to the elements labeled with the same subscript in FIG. Reference numeral 25 is a first wiring layer.

In the above structure, the thermal coupling PNP transistor 11 is arranged near the current mirror circuit composed of the PMOS transistors 2 and 3 and the NPN transistors 6 and 7 for sensing the ambient temperature. (Eighth Embodiment) FIG. 10 is a circuit diagram of the embodiment shown in FIG. 9, in which the second wiring 26 is used to further improve the ambient temperature sensitivity by using a collector and a PMOS as a part of the PNP transistor for thermal coupling. It covers the drain of the PMOS transistor 2 as part of a current mirror circuit consisting of transistors 2 and 3. (Ninth Embodiment) FIG. 11 is a modification of the embodiment shown in FIG. In FIG. 11, the second wiring layer 26 covers the entire PNP transistor 11 for thermal coupling. (Tenth Embodiment) FIG. 12 is a modification of the embodiment shown in FIG. In FIG. 12, the second wiring layer 26 covers a part of the thermal coupling PNP transistor 11 and the entire NPN transistor 6 as a part of the current mirror circuit composed of the NPN transistors 6 and 7. (Eleventh Embodiment) FIG. 13 is a modification of the embodiment shown in FIG. In FIG. 13, the second wiring layer 26 covers both the thermal coupling PNP transistor 11 and both emitters of the NPN transistors 6 and 7 as a part of the current mirror circuit composed of the NPN transistors 6 and 7. . (Twelfth Embodiment) FIG. 14 is a modification of the embodiment shown in FIG. In FIG. 14, the second wiring layer 26 covers the entire thermal coupling PNP transistor 11 and the entire current mirror circuit composed of the NPN transistors 6 and 7. (Thirteenth Embodiment) FIG. 15 is a modification of the embodiment shown in FIG. In FIG. 15, the second wiring layer 26 includes the entire PNP transistor 11 for thermal coupling, the current mirror circuit including the PMOS transistors 2 and 3 in addition to the NPN transistors 6 and 7, and the power supply (Vcc).
Is wearing

[0025]

As described above, according to the present invention,
By disposing the thermal coupling element in the vicinity of the current mirror circuit, sensing the ambient temperature, and feeding it back to the reference current, the temperature dependence of the output current can be reduced or eliminated.

Further, in the laser beam printer in which the laser drive current is determined by the output current of the current mirror circuit, the image density can be made uniform.

Further, by covering the thermal coupling element and at least part or all of the current mirror circuit with a common wiring layer, it is possible to improve the ambient temperature sensitivity of the thermal coupling element.

[Brief description of drawings]

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

FIG. 2 is a circuit diagram showing a second embodiment of the present invention.

FIG. 3 is a circuit diagram showing a modification of the embodiment shown in FIG.

FIG. 4 is a circuit diagram showing a modified example of the embodiment shown in FIG.

5 is a circuit diagram showing a modification of the embodiment shown in FIG.

FIG. 6 is a circuit diagram showing a modification of the embodiment shown in FIG.

FIG. 7 is a circuit diagram showing a modification of the embodiment shown in FIG.

FIG. 8 is a circuit diagram showing a modification of the embodiment shown in FIG.

FIG. 9 is a plan view showing a seventh embodiment of the present invention.

FIG. 10 is a plan view showing an eighth embodiment of the present invention.

11 is a plan view showing a modification of the embodiment shown in FIG.

12 is a plan view showing a modified example of the embodiment shown in FIG.

13 is a plan view showing a modified example of the embodiment shown in FIG.

14 is a plan view showing a modification of the embodiment shown in FIG.

15 is a plan view showing a modified example of the embodiment shown in FIG.

FIG. 16 is a diagram showing a conventionally known current mirror circuit.

FIG. 17 is a diagram showing a conventionally known cathode common type laser diode drive circuit.

[Explanation of symbols]

 1 Reference Current Source 2 PMOS Transistor 3 PMOS Transistor 4 Power Supply Vcc 5 Ground GND 6 NPN Transistor 7 NPN Transistor 8 Switching NMOS Transistor 9 Laser Diode 10 Control Signal Input Terminal 11 Thermal Coupling PNP Transistor 12 Resistor 13 Resistor 14 Resistor 15 Resistor 16 OP amplifier 17 NPN transistor 18 Reference current setting resistor 19 Thermal coupling NMOS transistor 20 PNP transistor 21 NPN transistor 22 NPN transistor 23 PNP transistor 24 PNP transistor 25 First wiring layer 26 Second wiring layer

Claims (6)

[Claims] 1. A current mirror circuit, a reference current source connected to the current mirror circuit, and a thermal coupling element disposed near the current mirror circuit for sensing an ambient temperature. A constant current supply device characterized in that temperature dependency of an output current of the current mirror circuit is reduced or eliminated by sensing ambient temperature by an element and feeding back to the reference current source. 2. The constant current supply device according to claim 1, wherein the output current of the current mirror circuit drives a semiconductor light emitting element. 3. The constant current supply device according to claim 1, wherein the thermal coupling element and at least a part or all of the current mirror circuit are covered with a common wiring layer. Constant current supply device. 4. A constant current supply device in which a plurality of stages of current mirror circuits are provided, and the output current of the current mirror circuit of the preceding stage serves as a reference current of the current mirror circuit of the succeeding stage. Arranging a thermal coupling element near at least one current mirror circuit, sensing an ambient temperature by the thermal coupling element, and feeding back to a reference current supplied to a current mirror circuit near the thermal coupling element. The constant current supply device characterized in that the temperature dependence of the output current of the current mirror circuit is reduced or eliminated. 5. The constant current supply apparatus according to claim 4, wherein the output current of the current mirror circuit at the final stage drives the semiconductor light emitting element. 6. The constant current supply device according to claim 4 or 5, wherein the thermal coupling element and at least a part or all of the current mirror circuits having a plurality of stages are covered with a common wiring layer. Characteristic constant current supply device.