JPS58225708A - Current mirror circuit - Google Patents

Abstract

PURPOSE:To improve the precision of a mirror circuit by adding a by-pass route wherein the collector current of the clamping transistor (TR) of an IC-implemented current mirror circuit is controlled. CONSTITUTION:A TRT4 is grounded directly at its emitter and connected at its collector to the emitter of a TRT1 to form the by-pass route 1. The base of the TRT4 is connected to the collector of the TRT1 and its base current is adjusted by a TRT5 and a resistance R4 connected between its collector and the ground. The collector and base of the TRT5 are short-circuited and it is used as a diode. The collector of the TRT4 is connected to the emitter (point P1) of the TRT1 to use some percentage of a current flowing to the point P1 as the collector current IC4 of the TRT4. The remainder is the emitter current of the TRT1, i.e. its collector current IC1 and base current IB1, but as the emitter current of the TRT1 is reduced, the IB1 is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to an integrated current mirror circuit, and in particular, the present invention relates to an integrated current mirror circuit, and in particular, a PNP transistor for base current supply and lamp, which has a lateral structure and has a small current amplification factor, is used for supplying a base current and for a lamp. The aim is to eliminate the influence on the symmetry of

Prior Art and Problems The current mirror circuit shown in FIG. 1 consists of a pair of transistors T2. When a constant current 1 flows through one T2 of T3, a current flows from the other T3 to the load so that a voltage equal to the voltage generated across the resistor R2 is generated across the resistor R3, and if R2=R3, the current I2 flows into the load. It is constructed by taking advantage of the fact that the value of is equal to 1, but when this is made into an IC, a PNP transistor T1
The current amplification factor β becomes a problem. Transistor T+ is transistor T2. It allows the base current to flow through T"3 and clamps its collector voltage so that the transistor T2 does not saturate. However, if there is a transistor T1, the base current flows into the constant current source 11. ,
This causes a deviation of the mirror current (2) from the planned value I5.

To explain these in more detail, the transistors TI, T
2. The base current of . . . is 'Bl, l112.・
..., the collector current is Ice, Ic2.・・・
..., the emitter current is 15. ,I)l,2. ...
..., PNP l-transistor T2. Since it is possible to give T3 the same characteristics, if R2=R・3, the connection shown in the diagram is 1112 IB3 r IF5 '= IF3 +
IC2'=IC3. Therefore 12 = IC3= IF5 Ina = Ic2=
IF5 1112= I + -I old
... Since the relationship ■ holds true, if IBl is sufficiently small, 12=I l, and the outflow current ■1 can be converted into the inflow current I2. However, PNP transistors in IC technology are generally of the lateral type and have a small current amplification factor β, resulting in a large base current. ) transistor T1 is connected to transistor T2.PNP). T
In addition to the purpose of supplying the base current 2.1B of transistor T2 (a resistor may be used as far as this goes), it also serves to clamp the collector potential of the transistor T2 so that it does not become saturated. That is, with respect to the emitter potential of the transistor T2, which is lowered by the voltage drop caused by the resistor R2 from the power source E1, the collector potential is further clamped to a value lower by 2 VBE to prevent saturation. 2 VBg is transistor T
＋.

This is the sum of the voltage between the base and emitter of T2. The emitter current I drawn by the transistor T+ used for this purpose
. 1 is the current flowing through the resistor R1 and the transistor T2. T
3 base current 1112. Since it is the sum of +113, β
If it is small, the base current l111 becomes large and the IBI of formula 0 cannot be ignored. Moreover, since there are manufacturing variations in β, the current (2) flowing through the load only includes errors due to IR resistance (it has the disadvantage that the variations vary from lot to lot).

OBJECTS OF THE INVENTION The present invention aims to solve the above-mentioned drawbacks without impairing the clamping function by adding a bypass circuit that can reduce the base current of the clamping transistor.

Structure of the Invention The present invention is characterized in that a constant current source is connected to one of a pair of transistors having the same characteristics and whose bases are connected in common, and a constant current is caused to flow therethrough. A current integrated circuit that has a circuit configuration that allows current to flow, and uses a first transistor that holds the transistor on the constant current source side in non-saturation as an element that flows the base current of the pair of transistors. In the mirror circuit,
a second transistor that bypasses a portion of the current drawn by the first transistor; and a diode-connected transistor that determines a current value to be bypassed to the second transistor from the current flowing between the collector and emitter of the first transistor. and a third transistor or diode, the base current of the first transistor is reduced so that the value of the mirror current approaches the constant current value. This will be explained in detail with reference to examples.

FIG. 2 shows an embodiment of the present invention, in which the circuit of FIG.
l-transistor T4. A bypass circuit consisting of T5 and resistor R4 is added. Transistor T4 has its emitter directly grounded and its collector connected to the emitter of transistor TI to form a bypass route.

The base of transistor T4 is connected to the collector of transistor T1, and its base current is adjusted by transistor T5 and resistor R4, which are connected in series between the collector and ground. The collector and base of the transistor T5 are short-circuited and used as a diode. Since the collector of the transistor T4 is connected to the emitter (point P+) of the transistor T1, a percentage of the current flowing into the point P1 is the collector current I of the transistor T4. 4
becomes. The remainder is the emitter current and therefore the collector current I of the transistor T1. 1 and the base current becomes 11,1, but
If the emitter current of TI can be reduced, 1111 can also be reduced.

In order to reduce the emitter current of transistor T+, it is sufficient to increase lC4, and the ratio (represented by Ic4/IC1) is determined by the following formula.

Here, v=r is a constant (V, , -k T / Q
) Te, approximately 26 mV at T-300°.

The above-mentioned current ratio can be arbitrarily set by the value of the resistor R4. For example, if Ic4/ic is set to 9, the collector current Ic1 becomes 1/10 in FIG.

Therefore, even if the current amplification factor β of the l-transistor T1 is the same, its base current IB1 can be reduced to 1/10.

In the circuit of FIG. 2, a resistor Ra (see FIG. 3) may be inserted between the emitter of the transistor T4 and the ground, and in this case, the current ratio 1c4/io can be set by the resistance ratio R4/Ro. However, as shown in FIG. 2, the resistor RI+ may be omitted; in this case, the transistor T4. The characteristic that VnE of T5 is proportional to the emitter current is utilized.

FIG. 3 shows another embodiment of the present invention, which is modified from FIG. 2 in the following three points. The first is PNPi transistor T1
A similar PNP) transistor T1' is connected to Darlington to increase the overall current amplification factor, thereby further reducing the base current in, r flowing into the constant current fil+ compared to 'IlH in Fig. 2. It is. The second is that the resistor R5 is added as described above to increase the degree of freedom in setting the current ratio 1c4/Icl, and the third is the transistor T3.
The same type of transistors T3', T3. ...
... is connected to amplify the current I2 flowing through the load to multiple times I-. All of these changes need not be adopted at the same time. Both resistors R4 and R5 may be omitted, and a plurality of transistors T4' and Ta may be connected in parallel, or their emitter areas may be changed. Also, the type of transistor in the entire circuit (P
NP, NPN) may be replaced. )
Effects of the Invention As described above, according to the present invention, the collector current of the clamping transistor of a current mirror circuit integrated into an IC is reduced by adding a controlled bypass route, and thereby the base of the transistor is reduced. Since the current can be made very small, there is an advantage that the precision of the mirror current can be improved.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an example of a conventional current mirror circuit, and FIGS. 2 and 3 are circuit diagrams showing different embodiments of the present invention. In the figure, TI is the first transistor for clamping, T2.
T3 is a pair of transistors, T4 is a second transistor for bypass, T5 is a diode-connected third transistor, I+ is a constant current source, and L is a load. Applicant Fujitsu Ltd. Representative Patent Attorney Minoru Aoyagi 3 Figure 1 F (Figure 2 1: +

Claims (2)

[Claims] (1) A circuit that connects a constant current source to one of a pair of transistors with the same characteristics and whose bases are connected in common and causes a constant current to flow, thereby causing a mirror current approximately equal to the constant current to flow through the load connected to the other. a first transistor that maintains the transistor on the constant current source side in a non-saturated state is used as an element that has a configuration and causes the base current of the pair of transistors to flow;
In an integrated current mirror circuit, a second transistor bypasses a part of the current drawn by the first transistor, and a current flowing between the collector and emitter of the first transistor is extracted from the second transistor. and a diode-connected third transistor or diode that determines a current value to be bypassed to reduce the base current of the first transistor to bring the value of the mirror current close to the constant current value. A current mirror circuit characterized by: (2) The current mirror circuit according to claim 1, wherein the first transistor is a Darlington-connected composite transistor.