JPS62145907A - Transistor circuit - Google Patents

Abstract

PURPOSE:To improve the current accuracy by inserting a resistor in series with a base of an input transistor (TR) in a current mirror circuit and utilizing a potential difference caused by the inserted resistor and the base current as the correction of an output current. CONSTITUTION:A resistor R2 is inserted to a base of an input TR Q1 and a potential difference is caused by the inserted resistor R2 and the base current of the input TR Q1. The potential difference acts just like increasing the base- emitter voltage of output TRs Q2, Q3 to increase output currents I2, I3. In selecting the inserted resistor R2 to make the increment of the output currents I2, I3 equal to the decrement of the output current due to the decrease in the grounded emitter current amplification factor hFE of the TRs Q1-Q3 to constitute a current mirror circuit where the output currents I2, I3 are independent of the factor hFE.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an improvement of a transistor circuit called a so-called current mirror circuit.

[Conventional technology]

A current mirror circuit is a circuit for obtaining an output current proportional to an input current, and its basic configuration is shown in FIG. Figures 5 and 4 are practical circuits that improve the basic configuration of Figure 2 to increase the number of output currents and improve stability. In both cases, an output current I2+ Is proportional to the input chamber iIt is obtained. It will be done.

Incidentally, examples relating to improvements in current mirror circuits include Japanese Patent Publication No. 11286/1983, Japanese Patent Publication No. 5287/1982, and Japanese Patent Publication No. 11408/1982.

[Problem that the invention seeks to solve]

Here, the operation and problems of the conventional circuit will be explained.

In FIGS. 2 to 4, transistors Qn (n=1 to
6) The emitter current and base current are respectively xEn,
IBn. In addition, it is assumed that the PNP transistors of Qt-Q4 have the same characteristics, and their common emitter chamber T
M, m width ratio is hpE. Furthermore, to simplify the calculation, it is assumed that REI = RE2 = RE3.

In Figure 2, Ir+ = IF5...
(3) Using equations (1) to (3) to find the relationship between h 1 and h 2, for example, when hrg = 10, the ratio of h 2 and L is ideal in the case where hFE is infinite. It can be seen that it cannot be used for circuits that require accuracy of 2. In Figure 3, (IE1 + IE2 + IE3) ... (
6) IEI = IF5 = IF3
...(8) From equations (5) to (8), if hpE = 10, then the ratio of E2 and If is approximately 97 in the ideal case.
%, which is an improvement over the case shown in FIG. 2, but this may not be sufficient depending on the circuit used. In addition, in the circuit shown in FIG. 3, when the collectors of Q2 and Q3 are oscillating with the signal voltage, the signal voltage of Q2. There is a risk that the frequency a characteristic will change due to leakage into the base of Q and 3, mutual crosstalk and feedback, or in severe cases, oscillation.

Figure 4 shows a circuit that improves the above (J) defect, with Q2 emitter follower. Since the base of Q3 has a low impedance, the 7χ phenomenon described above is unlikely to occur. Note that Q5 functions as a level shift and temperature compensation for Q6.

Assuming that the base-emitter voltages VBE of Q5 and Q6 are equal in FIG. 41, IEI "IF2 ・
...(12) The relationship between I3 and work 1 is also the same as in equation (13).

hpa=10. If IF5/IEI=1, then the current ratio is worse than in the case of FIG. (1
3) From the perspective of the formula, the current ratio can be improved by decreasing IF5, but in reality, decreasing IF5 will improve the temperature and h
Because the above assumption that the VBEs of Q5 and Q6 are equal no longer holds true due to the change in FE, no significant improvement can be expected.

As mentioned above, in conventional circuits, when hFE drops to about 10, the current ratio of L and 2 is not sufficiently close to 1, making it difficult to use in circuits that require high current value accuracy. Just in case.

An object of the present invention is to provide a parallel transistor circuit that can obtain a higher current value t#.

[Means for solving problems]

The above object is achieved by inserting a resistor in series with the base of the transistor on the input side and using the potential difference generated between the inserted resistor and the base current to correct the output current.

[Effect]

When the above correction voltage is applied so as to increase the voltage between the base and emitter of the output side transistor, the output current increases. By selecting the value of the insertion resistor such that the increase in output current is equal to the decrease in output current due to the decrease in hFE, it is possible to configure a transistor circuit in which the value of the output current does not depend on hFK.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG.

The circuit of the present invention differs from the conventional circuit shown in FIG. 3 in that a resistor R2 is inserted. If the same symbols and assumptions as in FIG. 5 are used in FIG. 1, equations (5) to (7) also hold true in FIG. 1, and furthermore, IE2RE2″Ir+Rεr +
IBIR2 is established. When the relationship between I3 and ■1 is determined from these equations, the relationship between I3 and ■1 is also the same as the equation (15).

If a value of R2 is selected such that the second terms of the denominator and numerator in equation (15) are approximately equal, I 2 /I 1 becomes approximately 1. For example, the relationship between hrg and I 2 /I 1 in the case of RE2 10 is shown in FIG. As can be seen from Fig. 5, for example, when hFE is 10 or more, I2/II in the circuit of Fig. 1 is 1.00 to t007, which is an improvement compared to the circuit l of Fig. 3. Recognize.

FIG. 3 is a circuit diagram showing another embodiment of the present invention, in which a resistor R3 is added to the circuit of FIG. 1. The circuit operation is the same as the circuit shown in FIG. 1, and equation (15) holds true as is. Resistor R3 works to reduce the influence of feedback of the closed circuit composed of Ql, Q4, and R3R2, and stabilizes the circuit.

FIG. 7 is a circuit diagram showing still another embodiment of the present invention, in which a resistor R2 is added to the circuit of FIG. 4. Using the same symbols and assumptions as in Figure 4, (10) ~ (
Equations 11) and (14) hold true. From these equations, we find the relationship between 12 and 1: rEIEI If we determine the value of R2 so that the following holds true, then hrE? hFE
In the range where the approximation of +1 holds true, the value of I2/work1 is approximately constant. For example, as in Figure 4, IF5/
If IEI = 1 and hpg = 10, then U and the value of I2/II is closer to 1 than in the case of FIG. The same holds true for the relationship between I3 and [Eng].

FIG. 8 is a circuit diagram showing still another embodiment of the present invention, in which a resistor R3 is added to the circuit of FIG. 7. In this case as well, the circuit operation is the same as in the case of FIG. 7, and equation (16) holds true as is, and the resistor R3 has the function of stabilizing the circuit as in the circuit of FIG.

In Figures 7 and 8, it has been assumed that the VBEs of Q5 and Q6 are equal, but in reality Q2. IF on Q3 hFE
6 may change and the above assumption may not hold. Therefore, the value of R2 is made larger than the value of formula (17), and the VB of Q6 is
It is also possible to compensate for changes in g to some extent.

Also, the assumption that REI = RE2 = Rr, a is for simplifying the explanation, and RE2 * Rg
Even if l is set to an arbitrary value, the effect of the embodiment is the same.

In addition, the number of transistors on the output side is all 2 in the embodiment.
Although this example shows three, the same effect can be obtained with one or three or more.

〔Effect of the invention〕

As described above, according to the present invention, the decrease in the output current caused by the decrease in the common emitter current amplification factor hFE of the transistor is compensated for by the potential difference due to the resistor inserted on the input side. The effect is that it remains almost constant regardless of the

[Brief explanation of drawings]

Figure 1 is a circuit diagram showing one embodiment of the present invention, Figures 2 to 4
The figure is a circuit diagram of a conventional example, FIG. 5 is a graph showing the relationship between hFE and I 2 / I l in the circuits of FIGS. 1 and 3, and FIGS. 3 to 8 are other embodiments of the present invention. FIG. Q1-Q4...PNP transistor Q5-Q6...NPN transistor R1-R3...Resistor Rgl -Rgl...
Resistor 11...Input current I2. I3...Output current I4...Current source 10B...Power supply 7''

Claims (4)

[Claims] (1) Connect the collector of a first PNP transistor whose emitter is connected to a common potential point via a first resistor to the base of a second PNP transistor whose collector is connected to ground; The emitters of two PNP transistors are connected to the base of the first PNP transistor through a second resistor to serve as a voltage reference point, and the emitters of one or more PNP transistors are connected to the common potential point through a resistor. The bases of the output side PNP transistors are commonly connected to the voltage reference point, and a current flows out from the connection point between the collector of the first PNP transistor and the base of the second PNP transistor, A transistor circuit characterized in that a current proportional to this current flows out from the collector of the output side PNP transistor. (2) The transistor circuit according to claim (1), characterized in that a resistor is inserted in series with the emitter of the second PNP transistor. (3) In claim (1), the first NP
connecting the emitter of the N transistor to the voltage reference point;
The base and collector of the first NPN transistor,
The collector is connected to the base of a second NPN transistor connected to the common potential point and also connected to the common potential point via a third resistor, and the emitter of the second NPN transistor corresponds to a current source. A transistor circuit, characterized in that the transistor circuit is connected to a circuit to serve as a second voltage reference point, and the bases of the output side PNP transistors are commonly connected to the second voltage reference point. (4) The transistor circuit according to claim (3), characterized in that a resistor is inserted in series with the emitter of the second PNP transistor.