JPH0138979Y2 - - Google Patents

Description

[Detailed description of the invention] [Field of industrial application] This invention suppresses the increase or decrease in output current due to the magnitude of the collector voltage of the output transistor in a current mirror circuit, especially a current mirror circuit implemented in a semiconductor integrated circuit. The present invention relates to a current mirror circuit that does not depend on the output voltage dynamic range of the circuit.

[Prior Art] FIG. 1 is a circuit diagram showing three examples of conventional current mirror circuits. In the figure, reference numerals 1 and 2 are transistors whose bases are commonly connected, and a reference current source 3 is connected to the collector of the transistor 1. Further, a drive transistor 4 for supplying base current is connected to the common base of these transistors 1 and 2, and its emitter is connected to the common base either directly or through an element such as a resistor in series, and the base of the drive transistor 4 is connected to a mirror. Reference current source 3 of the circuit
The collector of the drive transistor 4 is connected to the collector of the side transistor 1, and the collector of the drive transistor 4 is connected to the supply voltage Vcc terminal 5.
It is connected to the. Here, the output of the mirror circuit is constituted by the collector of the transistor 2, and normally a current that is a constant magnification of the reference current of the reference current source 3 is output. Note that 6 is a load resistance and 7 is an output terminal.

Next, the operation of the conventional circuit will be explained. In the figure, when the reference current Io is supplied from the reference current source 3, the base current of the drive transistor 4 flows, and the base current of the transistors 1 and 2 whose bases are connected together flows due to the collector current. , 2 are operated so that the voltage between the base and emitter of the two transistors becomes the same potential. Here, the voltage V _BE between the base and emitter of transistors 1 and 2 is
The voltage is determined by the reference current Io and the unique saturation current Is of the transistor 1 and is expressed by the following formula (1).

V _BE =kT/q・lnIs/Io...(1) k: Polzmann's constant T: Absolute temperature q: Charge Generally, in a mirror circuit, the output transistor 2 is a transistor with an emitter area that is a constant multiple of the reference current supply transistor 1. is used. Here, if the emitter area of the reference current supply transistor 1 is S and the area of the output transistor 2 is AS, then in the case of FIG. 1, the bases and emitters of transistors 1 and 2 are commonly connected, so Considering that the base-emitter voltages of the output transistors 2 and 2 are equal as shown in equation (1) above, and that the saturation current of the transistor is proportional to the emitter area, the collector current Ic of the output transistor 2 is V _BE =kT/q・lnIs/Io=kT/q・lnA・Is/Ic…(2), and Ic=AIo…(3). Therefore, the output current Ic is the reference current
It is A (area ratio) times Io and operates as a current mirror circuit with a constant magnification A.

[The problem that the idea aims to solve]

However, in the current mirror circuit with the above-described configuration, when the collector potential of the output transistor 2 changes in accordance with the resistance value of the load resistor 6, the DC current amplification factor increases due to the base width modulation effect (Early effect) of the output transistor 2. Since h _FE changes depending on the collector voltage, the output current of the output transistor (mirror output current) changes. In particular, the current amplification factor of transistors 1 and 2 that constitute the mirror circuit
h This is noticeable when _FE is high. Therefore,
The conventional circuit has a drawback in that the mirror output current changes depending on the bias voltage of the load, that is, the potential of the collector output of the mirror circuit, and a current that changes depending on the load is supplied.

Therefore, this invention was made in order to solve the conventional problems mentioned above, and its purpose is to attach the collector of the output transistor to
An object of the present invention is to provide a current mirror circuit in which the collector potential of the output transistor of the current mirror circuit is suppressed to a constant bias by connecting transistors whose bases are grounded in series, thereby eliminating the Early effect of the mirror circuit.

[Means for Solving the Problems] The current mirror circuit of the present invention includes a plurality of transistors whose bases are commonly connected, a drive transistor that supplies a drive current to the bases of the transistors, and one of the plurality of transistors. and a reference current supply means for supplying a reference current to the collectors of the transistors, and extracts a current equal to the reference current or at a certain magnification from the collectors of the output transistors other than the reference current supply side of the plurality of transistors whose bases are commonly connected. A current mirror circuit configured as follows, comprising a level shift transistor whose emitter is connected to the collector of the output transistor and whose collector is used as an output, and a constant current source which supplies a base potential to the base of the level shift transistor. It is.

[Effect]

In the present invention, by applying a DC bias potential to the base potential of the level shift transistor, a fixed DC bias voltage is applied to the collector of the output transistor, and the collector of the level shift transistor is used as an output.

〔Example〕

This invention will be explained in detail below using the drawings.

FIG. 2 is a circuit diagram showing an embodiment of the current mirror circuit according to this invention, and the same parts as in FIG. 1 are given the same symbols. In the figure, 8 is a level shift transistor connected in series between the output transistor 2 and the output terminal 7, and this transistor 8 has its emitter connected to the collector of the output transistor 2, and its base connected in series to the constant current source 9. Among the connected diodes 10a and 10b, diode 1
They are each connected to the anode side of 0a, and a constant DC bias is applied to the base.

FIG. 3 is a circuit diagram showing another embodiment of the current mirror circuit according to this invention, and the same parts as in the previous figure are given the same symbols. In this figure, the difference from FIG. 2 is that the reference transistor 1, the output transistor 2, the drive transistor 4, and the common base transistor 8 are composed of PNP transistors.

Next, the operation of the current mirror circuit according to this invention will be explained based on the embodiment shown in FIGS. 2 and 3. First, in FIG. 2, the base-grounded transistor 8 is connected to the collector of the mirror circuit output transistor 2, so that the collector voltage Vc ₂ of the output transistor 2 is changed from the base voltage V _B 8 of the common-base transistor 8 to the transistor 8
The value obtained by subtracting the base-emitter voltage V _{BE of} 8,
That is, it is expressed by the following formula.

_Vc2 = _VB8 - _VBE8 ...(4)= _2VD - _VBE8 ...(5) Here, _VD indicates the forward voltage of the diodes 10a and 10b.

Normally, the common base transistor 8 and the level shift diodes 10a and 10b for bias setting are of the same type of junction, such as a base-emitter junction, and have the same junction area. diode 10a,
The voltages are almost the same (V _D V BE 8) except for the voltage difference caused by the current difference between the bias current I ₉ that is DC-biased to 10b and the mirror output current Ic, and the voltage is almost the same (V D V _BE 8),
The formula is expressed as Vc ₂ ≒V _D (6). Therefore, even if the collector voltage of the common base transistor 8 changes due to the load, the emitter potential of the transistor 8, that is, the collector potential of the output transistor 2 of the mirror circuit remains constant. As the collector current of the mirror circuit output transistor 2 changes its voltage, there is no change in the collector current due to the Early effect (base width modulation effect) that normally occurs in the transistor 2.
Always held constant. On the other hand, the collector current of the level shift transistor 8 whose base is grounded is
Even if the collector voltage is applied due to the load, the collector current Ic ₈ of the transistor 8 and the diode 10a, 1
If the relationship with the current I ₉ of the bias current supply constant current source 9 of 0b satisfies the condition I ₉ ≫ Ic ₈ /h _FE (h _FE is the DC current amplification factor of the transistor 8), the collector of the output transistor 2 The current is the same as the current Ic, and is a constant current that does not depend on the collector voltage of the common base transistor 8.

According to such a configuration, it is possible to prevent the mirror output current from changing due to a change in the collector voltage of the mirror circuit output, which was a problem in the conventional circuit, and to reduce the junction area ratio between transistor 1 and transistor 2 of the reference current Io. The multiplied (A times) collector current Ic of the transistor 2 is output as the collector current (Ic ₈ Ic) of the transistor 8 without depending on the change in the collector voltage of the transistor 8 whose base is grounded.

Also, in FIG. 3, it operates in the same manner as described above,
The collector voltage of the output transistor 2 is clamped by the emitter of the common base transistor 8 to the DC voltage obtained by subtracting the base-emitter forward voltage V _BE (V _D ) from the power supply voltage Vcc.
Fluctuations in the mirror circuit output current (collector current of transistor 8) due to the Early effect (base width modulation effect) of output transistor 2 are suppressed, and a constant mirror output current can be extracted from the collector output of common base transistor 8.

In the above embodiment, the Early effect of the mirror circuit output is reduced by applying an appropriate bias to the common base transistor connected in series with the mirror circuit output. For example, diode 10
Replace the two series-connected diodes a and 10b with a resistor or a series connection of a resistor and a diode to expand the dynamic range of the mirror circuit, or connect one diode in series with the diodes 10a and 10b. However, applications such as making the collector potential of the output transistor 2 substantially the same as the collector potential of the reference current supplying transistor 1 can be easily configured while reducing the Early effect.

[Effect of idea]

As explained above, according to this invention, regardless of the magnitude of the output voltage of the mirror circuit, which changes depending on the size of the load, it is possible to always extract a current that is a constant multiple of the supplied reference current as the mirror circuit output. Therefore, extremely excellent effects such as wide application to circuits requiring a highly accurate current source can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an example of a conventional current mirror circuit, Fig. 2 is a circuit diagram showing an embodiment of the current mirror circuit according to this invention, and Fig. 3 is a circuit diagram showing another embodiment of this invention. It is. DESCRIPTION OF SYMBOLS 1... Reference current supply transistor, 2... Output transistor, 3... Reference current source, 4... Drive transistor, 5... Power supply terminal, 6... Load resistance, 7... Output terminal, 8... Level Shift transistor, 9... constant current source for supplying base bias voltage, 10a, 10b... diode.

Claims (1)

[Scope of utility model registration request] comprising a plurality of transistors whose bases are commonly connected, a drive transistor that supplies a drive current to the bases of the transistors, and a reference current supply means that supplies a reference current to the collector of one of the plurality of transistors; In a current mirror circuit configured to take out a current equal to or a certain magnification of a reference current from the collector of an output transistor other than the reference current supply side of the plurality of transistors whose bases are commonly connected, an emitter is connected to the collector of the output transistor. and a constant current source that supplies a base potential to the base of the level shift transistor, and applies a DC bias potential to the base potential of the level shift transistor, thereby increasing the output. A current mirror circuit characterized in that a fixed DC bias voltage is applied to the collector of a transistor, and the collector of the level shift transistor is used as an output.