JPS5977529A - Constant-current circuit - Google Patents

Abstract

PURPOSE:To obtain a stable constant-current by connecting each collector so that a current error portion of each transistor due to a voltage drop generated between each emitter is eliminated, by a circuit current flowing to a wire for connecting the emitter in common. CONSTITUTION:Influence by parasitic resistances r1, r2 and r3 is cancelled each other by using transistors TRQ1-Q4, connecting each collector of the largest TRQ4 and the smallest TRQ1 of a voltage drop generated by an earth current I0, and connecting each collector of the second and the third large TRs Q2, Q4 of the voltage drop. In this case, as for the resistances r1, r2 and r3, a ratio of its size can be set exactly by a shape of an aluminum wire 1, therefore, by selecting the ratio of the resistances r1, r2 and r3 and a value of the earth current I0, it is possible to constitute so that a constant-current value is not influenced by the earth current I0.

Description

[Detailed Description of the Invention] The present invention relates to a constant current circuit that obtains a constant current.
S V RR that suppresses voltage fluctuations in the power supply or ground on bamboo
(Supply Voltage Rejection
Ratio) This relates to a product that aims to improve the ratio.

FIG. 1 shows a conventional constant current circuit. In the figure, q] is a diode-connected transistor, Q2 is a transistor whose base and emitter are commonly connected to transistor Q1, r is the resistance of the wiring between both transistors Q+ r and the emitter of Q2, and IR is the reference current flowing through the transistor. The current Ia is the constant current flowing through the transistor Q2, I
a is the aluminum current, and ΔV is the voltage drop between both emitters due to the resistor 1.

Next, the operation will be explained.

In FIG. 1, the collector-base shorted transistor Q1 operates as a diode, and a constant current IO equal to the reference current IR flowing through this transistor (1) flows through the transistor Q. Ignore the base current of Q2 and steal 1-car transistor +
It is assumed that the Qt characteristics are the same.

When this constant current circuit is implemented using an integrated circuit (hereinafter referred to as an IC), the connections are as shown in FIG. In the same figure, the first
The same reference numerals as in the figure indicate the same parts, B is the base, E is the emitter, C is the collector, (1) is the aluminum wiring, and (2) is the contact.

Next, the operation will be explained.

The aluminum wiring (1) for connection has a finite resistance value,
It generally has a sheet resistance of about 50 mΩ. Therefore, the wiring (1) connecting the emitters E of transistors W+ and Q2 has a resistance r, and when the earth current IQ flows through this wiring (1), including current from other systems, this resistance r A voltage drop ΔV-rxla occurs across both ends. At this time, the reference current IR
The ratio between the constant current 10 and the constant current 10 is expressed by the following equation.

IO/1R-exP (Todoroki Δv) (1) where q is the electron charge, K is Boltzmann's constant, and T is the absolute temperature.

When △V is -2mV, "Ipt-1,08" is obtained, which is only 2mV (r-100mΩ, and IG-20m
A) (D Voltage drop jc causes an error of 8%,
The effect on constant current resistance is significant. In particular, if the earth current 1o contains an alternating current component, the above voltage drop △V will occur due to alternating current changes, and this voltage drop △V will be amplified by the transistor <22, resulting in a large error signal in the output. there were.

The present invention has been made in order to eliminate the drawbacks of the conventional ones as described above, and includes a constant current circuit including three or more transistors whose bases and emitters are all connected in common, and a wiring that connects the emitters in common. By connecting the collectors of the required transistors to each other so as to eliminate the current error of each transistor due to the flj pressure drop caused by the circuit current flowing in the circuit, we provide a constant current circuit that can improve the VRR performance by 1. It is intended to.

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

FIG. 3 shows a constant current circuit according to an embodiment of the present invention. In the figure, Q+, Qt, Q3. Q is a transistor whose base and O emitter are commonly connected, and among these transistors Q1 is diode-connected.

Also rll r2. rH is each transistor 90
See 21 Q31 What resistance does the wiring between the emitters of Q4 have? 1 (3 is the ground current, I ni1 standard weight '1AL
-IC is a constant current 1, 4th μm is the circuit shown in Figure 3.
The second rA turn is shown in the figure.
The same symbol indicates the same thing.

In the tree constant current circuit, the transistors Q, -Q, are
The collectors of the transistor Q4, which has the largest voltage drop caused by the earth current IQ, and the transistor Q1, which has the smallest voltage drop, are connected together, and the collectors of the transistors Q21Qa, which have the second and third largest voltage drops, are connected, and the parasitic resistance r1r r2. The effects of rH are tried to cancel each other out.

Here, the parasitic resistance '1+ "2+ rj is the aluminum wiring (1
), the size ratio can be set accurately depending on the shape of the resistors r, , r2. By selecting the ratio of rH and the value of the earth current IG, the constant current 1c can be set so as not to be influenced by the earth current 1a.

This embodiment is configured as described above, and although the number of transistors is increased compared to the conventional one, the transistors are integrated into ICs.
It is the cheapest component, that is, it has the smallest area, and therefore has a small impact on the overall cost increase.

FIG. 5 shows a constant current circuit according to another embodiment of the present invention, in which transistors Qt, Qs,) transistors Ql, Q4
In this example, transistors Q2 . Since it is common practice to have a common collector and base for transistors Q and transistors Ql and Q, respectively, two emitters can be formed in the same base. Therefore, compared to the embodiment shown in FIG. 3, the transistor area can be reduced by 7, and the matching %1 can be improved.

Note that the constant current circuit according to the present invention can also be constituted by a PNP transistor, and the S V RR due to the power supply current can be improved as in the above +Tc' embodiment.

Further, the constant current circuit may be constructed of a large number of transistor contacts, which are more than thin.In this case, even better effects can be obtained.

As described above, according to the present invention, three transistors constituting a constant current circuit whose bases and emitters are commonly connected are
In particular, in the case of a constant current source in an IC, the 5VRR It has the effect of significantly improving the % property.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a conventional constant current circuit, FIG. 2 is a pattern diagram when the circuit of FIG. 1 is integrated into an IC, and FIG. 3 is a circuit diagram of a constant current circuit according to an embodiment of the present invention. FIG. 4 is a pattern diagram when the circuit of FIG. 3 is implemented as an IC. FIG. 5 is a pattern diagram when the constant current circuit according to another embodiment of the present invention is implemented as an IC. Q, -Q,... Tongister, (1)... Aluminum wiring. Note that the same reference numerals in the figures indicate the same or equivalent parts. Agent Makoto Kuzuno - Procedural amendment (spontaneous) Commissioner of the Japan Patent Office 1, Indication of case Patent application 188558/1982
No. 2, Name of the invention Constant current circuit 3, Relationship with the case of the person making the amendment Patent applicant address East F, 2-1 Marunouchi, Chiyo ITI-ku, C
No. 12 No. 3 Name ((iol) Mitsubishi City Machinery Co., Ltd. Representative Katayuni Part 5, Detailed explanation of the invention in the specification subject to amendment 6, Contents of the amendment

Claims (1)

[Claims] (1) Comprising three or more transistors, at least one of which is diode-connected, and whose bases and emitters are all commonly connected, and a voltage drop that occurs between the emitters of the transistors due to a circuit current flowing through the wiring that commonly connects the emitters. A constant current circuit characterized in that the collectors of the required transistors are connected to each other so that the current error of each of the transistors due to the current error is eliminated.