JP3105716B2 - Current mirror circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current mirror circuit used for an FDD current drive circuit or the like.

[0002]

2. Description of the Related Art For example, in order to reliably erase magnetic data recorded on an FD in an FDD, it is necessary to always supply a constant current to an erase driver. Conventionally, a current mirror circuit shown in FIG. 2 has been used as a circuit for stably supplying a current to a device such as an FDD erase driver. This current mirror circuit includes a plurality of current mirror circuits, a current-to-voltage conversion circuit, and a voltage-to-current conversion circuit because it is necessary to supply a constant current of a certain magnitude. That is, a first current mirror circuit A including an NPN transistor,
The second current mirror circuit B includes a PNP transistor, a current-voltage conversion circuit C, an Early effect correction circuit D, a voltage-current conversion circuit E, and a third current mirror circuit F including a PNP transistor. . The first current mirror circuit A supplies the current supplied from the constant current source 77 to the second current mirror circuit B and the Early effect correction circuit D. Current supplied to the current mirror circuit B and Early effect correction circuit D, i.e., the collector current I _C of the transistor 59,62,66 constituting the first current mirror circuit A, the current from the constant current source I _IN , NPN transistor 59,
Assuming that the DC current amplification factors of 62 and 66 are h _FEN , I _C = I _IN − (3 · I _IN / h _FEN )...

The second current mirror circuit B has its collector connected directly to the collector of the transistor of the current mirror circuit A, and supplies the current supplied from the current mirror circuit A to the current-voltage conversion circuit C. The current-voltage conversion circuit C converts the current supplied from the current mirror circuit B into a voltage by the resistor 57, and applies a voltage obtained by adding 3V _BE of the transistors 53 to 55 to the voltage-current conversion circuit E.

The voltage-current conversion circuit E converts the voltages applied from the current-voltage conversion circuit C into transistors 70, 71, 7
Then, the voltage obtained by subtracting 3V _BE from the third is converted into a current by the resistor 72 and supplied to the current mirror circuit F. The transistors constituting the current-to-voltage conversion circuit C and the voltage-to-current conversion circuit E are supplied with current from the current mirror circuit F. As a result, the current flowing into the current-to-voltage conversion circuit C is converted by the current-to-voltage conversion circuit C This means that the signal is amplified and output by the two resistors of the conversion circuit E.

An Early effect correction circuit D is connected to the collector of the output transistor 70 of the current mirror circuit F. The Early effect correction circuit D converts the current from the current mirror circuit A into a voltage, and applies the voltage to the base of the output transistor 76 of the current mirror circuit F. As a result, the collector potentials of the output transistors 75 of the current mirror circuit F are made uniform, and an accurate output current is obtained. For example, a predetermined level of current is supplied from the output terminal 78 to the above-described FDD erase driver via a switching circuit (not shown).

[0006]

However, it has two current mirror circuits A and B as described above,
The conventional constant current circuit connecting the collectors of the transistors of each circuit has the following disadvantages.

That is, the collector current of the current mirror circuit A is obtained by removing the base current from the current flowing from the constant current source 77.
Since the DC current amplification factor h _FEN of the PN transistor changes depending on the ambient temperature, the collector output current of the current mirror circuit B also changes depending on the ambient temperature, and there is a problem that a stable output current cannot be obtained.

An object of the present invention is to cancel the temperature characteristic of the output current of one current mirror circuit by the temperature characteristic of the input current of the other current mirror circuit.
An object of the present invention is to provide a current mirror circuit that can always obtain a stable output current without being affected by an ambient temperature.

[0009]

A current mirror circuit according to the present invention comprises a first current mirror circuit comprising an NPN transistor and a second current mirror circuit comprising a PNP transistor. In a current mirror circuit connected by a collector of a transistor, only a common base of the first current mirror circuit and a common base of the second current mirror circuit are connected.
And a transistor to which the
Only the common base current of the two current mirror circuits is
The common current of the first current mirror circuit is connected via a transistor.
Characterized in that it flows as a source current .

[0010]

Now, assuming that the current from the constant current source is supplied to the first current mirror circuit composed of the NPN transistor, the current from the constant current source is supplied to the first current mirror circuit composed of the NPN transistor. Current mirror circuit and P
The signal is supplied to the output stage via a second current mirror circuit constituted by an NP transistor. When the DC current amplification factor of the NPN transistor constituting the first current mirror circuit increases with an increase in ambient temperature, the base current decreases, and the collector current of the base current supply transistor that supplies the base current, that is, The base current of the second current mirror circuit decreases. At this time, since the DC current amplification factor of the PNP transistor constituting the second current mirror circuit is also increased at the same time, even if the base current of the second current mirror circuit is reduced as described above, the second The collector current of the current mirror circuit is stabilized. That is, the decrease in the base current is canceled out by the increase in the DC current amplification factor in the second current mirror circuit, and the collector output of the transistor constituting the current mirror circuit has a stable value even when the ambient temperature increases. Become. On the other hand, when the ambient temperature decreases, similarly, the collector current of the transistor constituting the first current mirror circuit which tends to decrease is canceled by the base current of the transistor of the second current mirror circuit which tends to increase. , A stable output is always obtained with respect to temperature.

[0011]

FIG. 1 is a circuit diagram showing a configuration of a current mirror circuit according to an embodiment of the present invention. The current mirror circuit shown in the figure constitutes a part of a current drive portion of an integrated circuit for FDD as an example, and has an output terminal 28.
To supply a current to the FDD erase head through a switching circuit (not shown). The current mirror circuit A includes NPN transistors 9, 11, 12, 16 and resistors 10, 13,
The current supplied from the constant current source 27 is supplied to a current mirror circuit B and an Early effect correction circuit D, whose collectors are commonly connected. NPN transistor 11 as base current supply transistor
Has an emitter connected to the bases of the NPN transistors 9, 12, and 16 and a collector connected to the PN of the current mirror circuit B.
By connecting to P transistors 6 and 8, PNP,
Supplies base current to both transistors of the NPN.

The current mirror circuit B includes PNP transistors 6 and 8, and the current mirror circuit A
Is supplied to the current-voltage conversion circuit C. The base currents of PNP transistors 6 and 8 are set by NPN transistor 11.

The current-voltage conversion circuit C includes a transistor 3,
The current mirror circuit B is composed of the resistors 4, 5 and the resistor 7. The current from the current mirror circuit B flows through the resistor 7 and is converted into a voltage between both ends. This voltage is applied to 3V of transistors 3, 4 and 5.
_The voltage to which _BE is added is output to the voltage-current conversion circuit E. The current flowing through the transistors 3, 4 and 5 that determines the voltage value 3V _BE is supplied by the current mirror circuit F.

The voltage-current conversion circuit E includes a transistor 2
The voltage from the current-voltage conversion circuit C is input to the base of the transistor 20. From this base potential, transistors 20, 2
A current is output by dividing the voltage dropped by 3V _{BE of 1,} 23 by the value of the resistor 22. Transistor 2 that determines this 3V _BE
Currents flowing through 0, 21, and 23 are also supplied by the current mirror circuit F. That is, the output current of the voltage-current conversion circuit E is obtained by amplifying the output current of the current mirror circuit B by the ratio of the resistors 7 and 22.

The current mirror circuit F includes transistors 2, 19, 25 and resistors 1, 18, 24, and converts a current from the voltage-current conversion circuit E into an output current.

The Early effect correction circuit D includes transistors 14 and 26 and a resistor 15, and the current from the current mirror circuit A flows through the resistor 15 to convert it into a voltage. The emitter voltage of the transistor 26 is determined by the resistance value of the resistor 15, and this voltage is made equal to the collector voltage of the transistor 25 in the current mirror circuit F. By adjusting this voltage to the collector potential of the reference diode transistor 19 of the current mirror circuit F, a current error due to the Early effect is prevented.

In the above configuration, the DC current amplification factor of each transistor of the current mirror circuit A and the current mirror circuit B is h _{FE, which} has a positive temperature characteristic. Therefore, the base current decreases as the ambient temperature increases, and the collector current increases. Tries to get bigger. However, since the base current of the current mirror circuit A matches the base current of the current mirror circuit B, the collector output current of the PNP transistor 6 is stabilized with respect to the ambient temperature by adjusting the current value of the base current. Can be

Hereinafter, this operation will be described in detail. NPN transistors 9, 12, 16 constituting current mirror circuit A
The collector current, base current and emitter current, respectively I _iC, I _iB and I _{iE (i} Each transistor number)
Assuming that the DC current gain of the NPN transistor is h _FEN , I _11E = I _9B + I _12B + I _16B = 3 · I _12C / h _FEN . Considering that I _11B is sufficiently small, it is possible to obtain I _11E = I _11C , I _12C = I _IN ... Equation (3), and at this time, the second equation becomes I _11C = 3 · I _IN / h _FEN ... Equation 4 Since the DC current gain h _FEN has a positive temperature characteristic, the collector current I of the base current supply transistor 11 is
_11C will have negative temperature characteristics.

Next, assuming that the DC current gain in the PNP transistors 6 and 8 is h _FEP , the collector current of the transistors 6 and 8 is I _6C = I _8C = h _{FEP .I 11C} / 2 = (h _FEP. 3 · I _IN ) / (2 · h _FEN )... Accordingly, the temperature characteristics of the DC current gain h _FEP of the PNP transistor and the DC current gain h _FEN of the NPN transistor cancel each other, and the temperature characteristics of the collector current I _6C of the transistor 6 can be ignored.

In equation (5), the coefficient 3/2 on the right side is NPN
The area ratio of the transistors 9, 12, 16 and the resistance 10,
It can be determined by the size of 13,17. The DC current amplification factors h _FEN and h _FEP are constants determined by the process conditions, and the area ratio of the transistors 9, 12, and 16 and the resistances 10, 13, 1 according to the process.
By setting the magnitude of 7, the temperature characteristic of the output current of the collector current I _6C of the transistor 6 can be made zero.
The output current of the current mirror circuit B is supplied to the current-voltage conversion circuit C.

Note that the current mirror circuit of the present invention is
The same applies to circuits other than the DD integrated circuit. Further, the same effect can be obtained by replacing the current mirror circuit composed of the NPN transistor and the current mirror circuit composed of the PNP transistor.

[0022]

According to the present invention, the temperature characteristics of the DC current gain of the transistor due to the change in the ambient temperature can be mutually canceled in the two current mirror circuits, so that the influence of the ambient temperature on the output current is eliminated. This has the advantage that a stable output current can always be obtained at a constant value.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a current mirror circuit according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a conventional current mirror circuit.

[Explanation of symbols]

 A, B, F-current mirror circuit C-current-voltage conversion circuit D-Early effect correction circuit E-voltage-current conversion circuit 6,8-PNP transistor 9,12,16-NPN transistor

Claims (1)

(57) [Claims] 1. A current mirror circuit in which a first current mirror circuit formed of an NPN transistor and a second current mirror circuit formed of a PNP transistor are connected by a collector of one of the transistors. A common base of the first current mirror circuit and the second base;
To each of the common bases of the current mirror circuit
And a transistor having an emitter and an emitter connected thereto.
Only the common base current of the current mirror circuit is
A common base of the first current mirror circuit via the resistor
A current mirror circuit characterized by flowing as a current.