JPS63121913A - Current supply circuit - Google Patents

Abstract

PURPOSE:To reduce the transmission quantity of noise included in a reference current by reducing the AC gain of a current mirror circuit. CONSTITUTION:When a reference current Iref is inputted to a transistor TR Q11, and N-fold current I2 is taken out from a TR Q12. Meanwhile, the output current of the TR Q11 is turned back by a second current mirror circuit and is added to the output current I2 of the TR Q12 to become a bias current IB of a TR Q15. Since the voltage of an emitter resistance R2 connected to the TR Q15 is determined by the emitter area ratio of TRs Q11 and Q12 and that of TRs Q13 and Q14 in this case, the emitter resistance value is increased and the voltage value is increased to reduce the AC gain of the TR Q15, and the noise component included in the reference current is so reduced that it cannot appear in the output current.

Description

Detailed Description of the Invention [Object of the Invention] (Industrial Application Field) The present invention relates to a current supply circuit that supplies a current to a load according to a reference current.

(Prior Art) Conventionally, a current supply circuit as shown in FIG. 5 has been often used in electronic circuits. This circuit connects the collector and base of transistor Q1 in common to form a diode configuration,
This transistor and a plurality of (here, three) transistors Q2. A current mirror circuit is constructed by connecting the bases of Q3 and Q4 in common, and by supplying a reference current of 1 rat' from the current source IO to the transistor Q1, the voltage from the collector of each transistor Q2 to Q4 is A predetermined output current (load current) I outl=I out3 is supplied to the load L (consisting of a plurality of load circuits). Each of the output currents 1 outt to I out3 can be set to a desired current value by appropriately setting the emitter areas of the transistors Q2 to Q4, respectively.

The general formula is I out = N ◆I rcf', ignoring the base current of each transistor Q2 to Q4 and assuming that the emitter area ratio to Ql is N. That is, the reference voltage tTLI raf' and the output current I out are in a proportional relationship as shown in FIG.

However, in the conventional current supply circuit as described above,
Since the reference current and the output current are in a proportional relationship, if the reference current contains noise, the noise component will be increased according to the emitter area ratio and will appear in the output current, and will be transmitted to the load.

(Problems to be Solved by the Invention) This invention was made in order to improve the problem that in conventional circuits, when noise is included in the reference current, the noise component is increased in accordance with the emitter area ratio and transmitted. An object of the present invention is to provide a current supply circuit that can reduce noise components contained in a reference current so that they do not appear in an output current.

[Structure of the Invention] (Means for Solving the Problems) A current supply circuit according to the present invention supplies current to a load according to an output current of a reference current source, in which a collector and a base are commonly connected. a first transistor having a connection point connected to the output end of the reference current source; a base connected to the base of the first transistor and a collector connected to a first power supply; and the first transistor having an emitter area. and a second transistor having a large collector and base, the collector and base of which are connected in common, the connection point is connected to the emitter of the first transistor, and the emitter is connected to a second power source having a different potential from the first power source. a third transistor; a fourth transistor having a base connected to the base of the third transistor and a collector connected to the emitter of the second transistor; and a fourth transistor having one end connected to the emitter of the fourth transistor. a first emitter resistor whose other end is connected to the second power supply; and a base which is connected to the second power supply;
a fifth transistor whose collector is connected to the emitter of the transistor and whose collector is connected to the input terminal of the load; and a fifth transistor whose one end is connected to the emitter of the fifth transistor and whose other end is connected to the second power supply. 2 emitter resistors.

(Function) The current mirror circuit according to the configuration described in 1- above has a first and a second
A first current mirror circuit composed of transistors extracts a current obtained by multiplying the reference current flowing through the first transistor by the emitter area ratio of the second transistor, and outputs a current that is multiplied by the emitter area ratio of the reference current flowing through the first transistor. A second current mirror circuit consisting of a second current mirror circuit returns and outputs the current flowing through the first transistor, and adds each output current of the first and second current mirror circuits to a fifth transistor for supplying load current. The bias current is set to .

In this case, the voltage related to the second emitter resistor connected to the fifth transistor is determined by the emitter area ratio of the first and second transistors and the emitter current ratio of the third and fourth transistors, so this emitter resistor By increasing the value and increasing the voltage value, the AC gain of the fifth transistor can be decreased, and thereby the amount of noise transmitted in the reference current can be reduced.

(Embodiment) Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1 to 3.

FIG. 1 shows the basic configuration of the present invention, where 10 is a reference current source and L is a load. Q11. Q12 is a transistor that constitutes the first current mirror circuit, and Q12 is a transistor that constitutes the first current mirror circuit.
The collector and base of ll are commonly connected, and the connection point is connected to the output end of the reference current source. The base of Ql2 is connected to the base of Qll, and the collector is connected to the +■CC power supply. The emitter area ratio of Qll and QI2 is 1:
It is N.

Q13. Q14 is a transistor constituting a second current mirror circuit, Q13 has its collector and base commonly connected, the connection point is connected to the emitter of Qll, and the emitter is connected to earth GND.

The base of Q14 is connected to the base of Q13, the collector is connected to the emitter of Q12, and the emitter is connected to earth GND via an emitter resistor R1.

Q15 is a transistor that outputs the load current I out, and its base is connected to the emitter of 012, its collector is connected to the input terminal of the load, and its emitter is connected to earth GND via a second emitter resistor R2.

The operation of the above configuration will be explained below.

First, when a reference current 1 rcf' is input to the transistor Qll that constitutes the first current mirror circuit, a current N times that amount flows from the transistor Q12! 2 is taken out.

On the other hand, the output current of Qll is reflected by the second current mirror circuit and added to the output current I2 of Q12,
The bias current IB becomes 15.

In this case, the emitter area ratio of Qll, Q12 and 01
3゜The voltage related to the emitter resistor R2 connected to Q15 is determined by the emitter current ratio of Q14, so if this emitter resistance value is increased and the voltage value is increased, Q14 is determined by the emitter current ratio.
15 AC gain can be made small.

In other words, the base of transistor Q15 and the ground GND
The potential difference between them is VX, and the reverse saturation current of Qln is Is
When n is the Raman constant, T is the absolute temperature. Qll, Q13. Since the emitter and ivy areas of Q15 are the same and Q12 has an emitter area N times that of Qll, formula (1) can be summarized as...
(2) becomes. Since I out cannot be determined algebraically from equations (2) and (3), it is necessary to substitute the actual values and solve numerically. For example, N-25, R2-1
As [kΩ], the output current I2 of Q12 is 2 of I rcr
The I rar vs. I Out characteristics when doubled are shown in FIG. By providing such characteristics, the AC gain of the transistor QL5 becomes small within the range where the slope of the curve in FIG. 2 is 1 or less.

Therefore, in the current output circuit configured as described above, since the AC gain of the current mirror circuit is small, it is possible to reduce the amount of transmission of noise components included in the reference current I rer.

FIG. 3 shows a configuration in which the present invention is applied to the conventional circuit shown in FIG.
2 to Q4 are connected to emitter resistors R12 to R14, respectively. According to this, each load current outl
It is possible to reduce a noise component that is N times the noise generated in the reference current 1 red' appearing at -1out3.

Note that this invention is not limited to the above embodiments,
For example, as shown in FIG. 4, all of the circuits in FIG. 3 may be constructed with opposite polarities. In FIG. 4, elements corresponding to those in FIG. 3 are given the same reference numerals, and their explanations will be omitted.

[Effects of the Invention] As described above, according to the present invention, it is possible to provide a current supply circuit that can reduce the noise component contained in the reference current so that it does not appear in the output current.

[Brief explanation of the drawing]

FIG. 1 is a basic circuit diagram showing one embodiment of the current supply circuit according to the present invention, FIG. 2 is a characteristic diagram showing an example of the fundamental current vs. output current characteristic of the same embodiment, and FIGS. 3 and 4. is a circuit diagram showing another embodiment according to the present invention, FIG. 5 is a circuit diagram showing the configuration of a conventional current supply circuit, and FIG. 6 is a characteristic diagram showing an example of the reference current versus output current characteristic of the conventional circuit. be. I rel'...Reference current source, L...Load, Q1~
Q4゜Qll-Q15...Transistor, R1, R2
...Emitter resistance. Applicant's agent Patent attorney Takehiko Suzue Figure 1 Iref [)AA] Figure 2 Figure 3 Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] In a current supply circuit that supplies current to a load according to an output current of a reference current source, a first circuit whose collector and base are commonly connected and whose connection point is connected to the output end of the reference current source
a transistor whose base is connected to the base of the first transistor and whose collector is connected to a first power supply, and the first transistor has a collector and base commonly connected to a second transistor having a large emitter area. a third transistor whose connection point is connected to the emitter of the first transistor and whose emitter is connected to a second power source having a different potential from the first power source; and a third transistor whose base is connected to the base of the third transistor. a fourth transistor whose collector is connected to the emitter of the second transistor; and a first emitter whose one end is connected to the emitter of the fourth transistor and the other end is connected to the second power supply. a resistor; a fifth transistor having a base connected to the emitter of the second transistor and a collector connected to the input terminal of the load; one end connected to the emitter of the fifth transistor and the other end connected to the fifth transistor; 1. A current supply circuit comprising: a second emitter resistor connected to a second power source.