JPS6261410A - Current mirror circuit - Google Patents

Abstract

PURPOSE:To decrease the variation of a current mirror output current by providing a negative feedback circuit applying negative feedback from a collector to a base of an input transistor (TR) so as to prevent the effect of the early effect and the effect of the base current component. CONSTITUTION:Each base of plural reference TRs Q2a, Q3a is connected in common to a reference TR Q1a, each emitter of the reference TRs Q2a, Q3a is connected to a VCC power supply and each emitter of PNP output TRs Q2b, Q3b is connected corresponding to each collector. Then a diode D1 generating a prescribed voltage drop is connected between the base of the reference TR Q1a and the base of an input TR Q1b. Further, a differential amplifier 4 is provided as a negative feedback circuit to apply base current correction of the input TR Q1b and output TRs Q2b, Q3b and to correct the variation of the current amplification factor beta of each TR.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a current mirror circuit used as a current source circuit in an I7 air integrated circuit or the like, and particularly to a circuit improved to reduce the influence of the Early effect.

[Technical background of the invention]

FIG. 10 shows a conventional current mirror circuit including one PNP input transistor Q1 and two output transistors Q! - Each base of Q3 is shown commonly connected. The input transistor Qs has an emitter of V
ce power source, the base and collector are connected to each other, and a reference current source 1 for flowing a reference current I ref is connected between the collector and the ground terminal. The output side transistors Q2 and Q3 each have their emitters connected to the Vce power source, and their collectors connected to loads 2 and 3, respectively.

In the above current mirror circuit, load 2.

Output transistor Q at 3! A current mirror output current from #Q3 is applied to cause a voltage drop, and the collector voltages of the output transistors Qx and Q3 are determined accordingly. Therefore, when a resistor with a resistance value R is connected as load 2 and a resistor with a resistance value of about 2 is connected as load 3, the collector mutual pressure vc, of the output transistor Qs is 2 of the collector voltage Qc, of the output transistor Q1. It will be doubled. Furthermore, when a transistor whose collector and base are connected together is connected as the load 2, and a resistor with a resistance value R is connected as the load 3, the voltage drop Vile of the load transistor is approximately equal to the change in the applied current rref. Since it is determined by a logarithmic relationship (VBg ``tref vTtn-T, -), it is relatively difficult to change.

On the other hand, the voltage drop Ir. Since fXR changes depending on the current I ref and the resistance value R, the collector voltages of the output transistors Qx and Qs differ.

[Problems with background technology]

However, as mentioned above, the output transistors Qz, Q
When the respective collector voltages of s are different, a difference occurs in the respective collector-emitter voltages VcΣ2 e VCIC3, and when the early voltages of the transistors Qz and Qs are low, they are greatly affected by the early effect, and the output transistors Qt, There was a problem that each output current of Qs was not the same but varied. Here, the Early effect refers to the voltage VCE between the collector and emitter of the transistor shown in FIG. As can be seen from the static characteristics of
3, the collector current is re, r rc
, say different things like .

Furthermore, in the conventional current mirror circuit, the input transistor Ql and the output transistor Q! ,Q
If each base current of 3 is ignored, the current mirror output current will be equal to the reference current Iref, but strictly speaking, it will be affected by the current amplification factor β of the transistor, and the output transistor Qz
The output current of yQs is 9, respectively, and there is a problem that the current mirror output current varies due to the variation in β. In particular, when the current mirror circuit is multi-staged (when the number of output transistors is increased), each base current of many transistors is drawn into the reference current source 1, so the base current component of each transistor cannot be ignored, and the input transistor There is a problem in that the collector current of Q1 becomes isometrically small, and as a result, the current mirror output's ridge current also becomes small.

[Purpose of the invention]

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a current mirror circuit that can prevent the influence of the Early effect and the influence of the base current component, and can reduce variations in the current mirror output current. be.

[Summary of the invention]

That is, the current mirror circuit of the present invention connects each emitter of a plurality of reference transistors whose bases are commonly connected to the first
one input transistor and a plurality of output transistors whose bases are connected in common, each emitter of the plurality of reference transistors is connected correspondingly to each collector of the plurality of reference transistors, and the emitter of the input transistor is connected to the power source of the input transistor. A reference current source is connected between the reference transistor group and the second power source, a circuit element is connected that produces a constant voltage drop between the base common connection point of the reference transistor group and the base of the input transistor, and the input transistor The device is characterized by being provided with a negative feedback circuit that applies negative feedback from the collector to the base.

As a result, each collector-emitter voltage of the reference transistor group becomes equal to the voltage drop of the circuit element and becomes constant, so that it is not affected by the earth effect and the current mirror output currents become equal. Further, since the base current component of each transistor is corrected by the negative feedback circuit, it is not affected by variations in the '1st current amplification factors of each transistor, and variations in each current mirror output current are reduced.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

In Figure 1, there is a PNP between the Vce power supply and the ground terminal.
Reference transistor Qx&, input transistor Q
lb and a reference current source l for flowing the reference current Iref.
are connected in series. The above reference transistor Qxa
has a plurality of (two in this example) reference transistors Qxa.
The bases of the reference transistors Qza+Qsa are connected in common, the emitters of the reference transistors Qza+Qsa are connected to the Vcc'dL source, and the emitters of the PNP output transistors Qmb r Qsb are connected to the respective collectors. .

Each base of the output transistor Qzbr Qsb is commonly connected to the base of the input transistor Q1b, and a load 2.3 is connected to each collector correspondingly. A diode D, for example, is connected between the base of the reference transistor Q+a and the base of the input transistor Qlb as a circuit element for generating a constant voltage drop.

Furthermore, the differential amplifier 4 is used as a negative feedback circuit to correct the base currents of the input transistor Q1b and the output transistors Q, b, and Q3b, and to correct variations in the current amplification factor β (or hfe) of each transistor. is provided. The non-inverting input terminal (+) of this differential amplifier 4 is connected to the collector of the input transistor Qtb, the inverting input terminal (-) is connected to the variable bias source 5, and the output terminal is connected to the base of the input transistor Qtb. It is connected to the.

In the above current mirror circuit, each emitter of the reference transistor Q1m+input transistor Q1b and R-
The voltage across VIIK, diode D, and reference transistor QIA is vec −V!1m −Vx+VB!=vc,
vx and the reference transistor Qla t Qza
+ The collector-emitter voltage VCW of each Q port is “ee”
−(vee −vx) = “X” is constant. Therefore, the reference transistor Qra + Qza + Qs
The respective collector currents of a are equal, and a current mirror output current that is equal to the reference voltage filraf flowing to the input transistor Qxb flows through the output transistor Qxb + Qsb. That is, each current mirror output current is not affected by the Early effect, and the variation is reduced, and a highly accurate current mirror output DC can be obtained in a wide power supply voltage usage range.

Further, a negative feedback effect is performed by the differential amplifier 4 so that the common connection point of the bases of the transistors Qtbl Qsar Qsb, which are the output terminals thereof, is kept at a constant potential. That is, when the base current of the transistor group increases, for example, the current flowing into the output terminal of the differential amplifier 4 increases, and the output terminal potential tends to decrease. However, at this time, if the collector current of the input transistor Qtb is small,
Since the collector voltage becomes high, correction is performed to increase the output terminal potential. This negative feedback effect corrects the base current of the transistor group,
The variation in current amplification factor β (or hfe) of the transistor group is corrected.

Figure 2 shows a circuit modified from the circuit in Figure 1 so that the polarity of the transistor is reversed (PNP type → NPN type), and the same parts as in Figure 1 are designated by the same symbols. Attached,
1. Portions corresponding to those in FIG. 1 are indicated with a ``" added to the reference numerals in FIG. 1.

FIG. 3 shows a specific example of the differential amplifier 4 in which a resistor R is used in place of the diode D in the circuit shown in FIG. If the voltage drop VX occurring across the resistor R1 is small, the reference transistor Qlh a Qta +
Since the collector-to-emitter voltage vc of Qsa becomes small and the operation of the reference transistor group enters the saturation region, the voltage drop vx is increased so as not to enter the saturation region (so that it is above the saturation region). It is necessary to set it somewhat large.

The differential amplifier 4 has a differential pair of transistors Q4-Qs of opposite polarity (NPN type in this example) to the reference transistor group, input transistor group, and output transistor group, and a common connection point between the emitters of these transistors Qa-Qs. It consists of a constant current source connected. One transistor Q4 has a collector connected to the VCC power supply and a base connected to the collector of the input transistor Qtb, and the other transistor Q6 has a base connected to the bias power supply 5 and a collector connected to the input transistor Qtb. connected to the base of. The operation of this differential amplifier 4 is the same as the operation of the differential amplifier 4 explained with reference to FIG. The effect of is negligible.

FIG. 4 shows a circuit modified from the circuit in FIG. 3 by reversing the polarity of the transistors, and the same parts as in FIG. Corresponding parts are indicated by the reference numerals in FIG. 3.

FIG. 5 shows a circuit modified from the circuit shown in FIG. 3 so that the output of the differential amplifier 4 is received by a current mirror load circuit 6. Here, the current mirror load circuit 6 is
The emitters of the transistors Qs and Qγ, which have opposite polarity (PNP type in this example) to the differential pair transistors, are connected to the Vcc power supply, and the collector of the input side transistor Q6, whose base and collector are connected to each other, is connected to the differential pair transistor. It is connected to the collector of one transistor Q4, and the collector of the output side transistor Qγ is connected to the reference transistor Q+a.
r Qsa r Connected to the base common connection point of Qsa.

Figure 6 shows the circuit in Figure 5 [which has been modified so that the polarity of the transistors is reversed, and the same parts as in Figure 5 are given the same symbols, Corresponding parts are marked with "" in the reference numerals in FIG.

FIG. 7 shows a current mirror circuit using a transistor Qa, a current source 71, and a diode D chamber as a negative feedback circuit 7, and has three output stages.
is the reference transistor, Qab is the output transistor, 8
is a load group, and the others are given the same symbols as in FIG. The negative feedback circuit 7 includes an input transistor Qtb
is connected to the ground terminal via a current source 7, its base is connected to the collector of an input transistor Qtb, and a diode D is connected between the base of this input transistor Qsb and the current source 7. Become. Therefore, when the collector voltage of the input transistor Qtb increases, the emitter voltage of the trannostar Q8 increases, and the diode D
! Through this, the base voltage of the input transistor Qsb is corrected in the direction of increasing, and a desired negative RR effect can be obtained.

Note that a resistor or a variable DC power supply circuit may be used in place of the diode D, and a resistor may be used in place of the current source 71.

FIG. 8 shows the diode DI+D! for the circuit of FIG.
This shows a modified circuit in which a resistor R1pR1 is used instead of , and the polarity of the transistor is reversed. The same parts as in FIG. 7 are given the same reference numerals, and the corresponding parts as in FIG. The symbols in FIG. 7 are appended with '.

Figure 9 shows that the diode DI+D2 is different from the circuit in Figure 7.
The difference is that a resistor RIIR is used instead of , and a resistor R3 is connected as a load of the negative feedback circuit 1 between the vcciat source and the common base connection point of the reference transistor group.

〔Effect of the invention〕

As mentioned above, according to the Karen 2L circuit of the present invention,
In addition to being able to prevent the influence of the Early effect, it is also possible to prevent the influence of the base current component, and it is possible to reduce variations in the current mirror output current.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing one embodiment of the current mirror circuit of the present invention, FIGS. 2 to 9 are circuit diagrams showing modified examples or other embodiments of the present invention, and FIG. 10 is a circuit diagram of a conventional current mirror circuit. A circuit diagram showing a mirror circuit, and FIG. 11 is a characteristic diagram shown to explain the Early effect. Qxa + Qga + Qsa t Qaa ・"Reference transistor, Qtb - input transistor, Qaa
l Qsb + Q4b...output transistor,
DltD...Diode, R1, R1...Resistor,
DESCRIPTION OF SYMBOLS 1... Constant current source, 4... Differential amplifier, 5... Bias power supply, 7... Negative feedback circuit, Q4, Qs-
Qs...transistor, 3...constant current source, 7
No... Current source. Applicant's representative Patent attorney Takeshi Suzue Pig box 2 Figure 4

Claims (4)

[Claims] (1) A plurality of reference transistors each having an emitter connected to a first power supply and each base commonly connected, and each emitter corresponding to each collector of the plurality of reference transistors being connected and each base commonly connected. one input transistor and a plurality of output transistors, a reference current source connected between the collector of the input transistor and a second power supply, and a base common connection point of the reference transistor group and the input a circuit element that is connected between the base of the input transistor and produces a constant voltage drop; and a negative feedback circuit that receives input from the collector of the input transistor and provides a negative feedback output to the base of the input transistor. , a current mirror circuit characterized in that the collector current of the output transistor is a current mirror output. (2) The negative feedback circuit includes a differential amplifier whose non-inverting input terminal is connected to the collector of the input transistor and whose output terminal is connected to the base of the input transistor, and an inverting input terminal of the differential amplifier. 2. The current mirror circuit according to claim 1, further comprising a bias power supply connected to the current mirror circuit. (3) The negative feedback circuit includes a differential pair of transistors having a polarity opposite to that of the transistor group, a current source connected between a common emitter connection point of the differential pair of transistors, and a second power source; a bias power supply connected to the base of one of the differential pair transistors;
The collector of one of the transistors is connected to the base of the input transistor, the base of the other transistor of the differential pair transistors is connected to the collector of the input transistor, and the collector of the other transistor is connected to the first power source. 2. The current mirror circuit according to claim 1, wherein the current mirror circuit is connected to the current mirror circuit. (4) The negative feedback circuit has a base connected to the collector of the input transistor, a collector connected to a first power supply, a transistor having a polarity opposite to that of the reference transistor group, an emitter of this transistor, and a second A current source or a resistor connected between the power supply of the transistor and a diode or a resistor or a variable bias power supply circuit connected between the emitter of the transistor and the base of the input transistor. A current mirror circuit according to claim 1.