JPH02285410A - Current dividing circuit - Google Patents

Abstract

PURPOSE: To determine a division ratio of a current by only a ratio of resistance values by making desired one of plural current ratio determination circuits selectively operatable by a control terminal. CONSTITUTION: Each of plural current ratio determination circuits is provided with third and fourth transistors TRs Q3 and Q4. The third TR Q3 has the collector connected to a second current output terminal and has the emitter connected to a current input terminal through a resistor RS for current ratio determination and has the base connected to the control terminal, and the fourth TR Q4 has the corrector connected to a voltage source and has the base connected to the emitter of the third TR Q3 and has the emitter connected to a current source and forms a differential pair together with a second TR Q2. The emitter of a first TR Q1 and that of the selected third TR Q3 are set to the same potential. Thus, a current ratio is determined independently of TRs by only the value of the resistor.

Description

[Detailed description of the invention] [Industrial application field] TECHNICAL FIELD The present invention relates to a current dividing circuit.

More specifically, it relates to a current dividing circuit that digitally controls the current ratio with high precision.

[Prior Art and Problems to be Solved] A DA converter can be used for accurate current control, such as write current control to a magnetic head for reading a floppy disk. However, such DA converters often require fairly complex circuit configurations and large power consumption, making them large and expensive. In particular, devices using batteries as a power source are desired to have lower power consumption, and as devices become more widespread, more economical methods are also desired. Therefore, a current dividing circuit using an IC as illustrated in FIG. 4 has conventionally been used. A voltage v8 is commonly applied to the bases of a pair of transistors Q1 and Q3 included in this circuit, and both base potentials are made equal. A current I, flows from the first current output terminal 14 to the collector of the transistor Q1, and a current I, flows from the second current output terminal l6 to the collector of the transistor Q3. The emitter current of both transistors I. together constitute IIN and flow to the current input terminal 12. Both HFEs of both transistors are sufficiently large and E t#I
Let C be the pace emitter voltage of Ql:
1, Q2's pace emitter voltage is expressed as V IIE3, and the following equation holds true.

I+Rr+Va! + = I 3 Rs + VIIE
3 f1) Also, since I++Is=I+ (21 holds true), ■, I3 can be obtained from equations (1) and (2).

I += (I+sRs+V!lts-Vac+)/
(Ra+RrlI a ” ( 1 +sR F +V
at+ −VBE31/(R 11 + RFI...
...(3) As shown in the above equation, a term related to VBE is included in the equation for determining 1 and , and this is a factor that depends on the size and current of the transistor. , controllability becomes very poor when changing the division ratio. For example, Figure 5 shows a conventional circuit that uses digital signals to control the division ratio. Control terminals 18A, 18
Turn on any one transistor Q3 by applying an appropriate logic voltage level to B...
You can select one block and pause the others. In this way, 1. /1. When changing the division ratio of , there is a term related to VIIE as shown in equation (3) above, which is complicated, so in order to obtain an accurate division ratio, the division ratio is actually limited to an integer, and it is free Even in cases where the degree is very low and the ratio is an integer, 1. /1. In order to obtain a large division ratio of , it is necessary to prepare a large transistor or a plurality of transistors corresponding to the current due to the existence of the Vag term, which is an economic disadvantage.

In view of the above-mentioned problems, an object of the present invention is to provide a current dividing circuit that is compact, has a high degree of freedom, and has good controllability.

Another object is to provide a current dividing circuit as described above, which consumes less current and can be miniaturized.

[Means for solving problems]

In order to achieve the above object, a current dividing circuit according to the present invention is provided.

Current output terminal (121; first and second current output terminals (14, 16) for the current to be divided; two control terminals (1
8) a first transistor (Q1) whose collector is connected to the first current output terminal and whose emitter is connected to the current input terminal via a resistor (RF); the collector is connected to the first transistor; is further connected to a voltage source (Vcc) via a current source (17), the base is connected to the emitter of the first transistor, and the emitter is connected to a current source (19). a second transistor (Q2) and a plurality of selectable current ratio determining circuits, each of which is connected to a third transistor (Q2);
Q3) and a fourth transistor (Q4), the third transistor has a collector connected to the second current output terminal and an emitter connected to the current input terminal via a current ratio determining resistor (R3). The fourth transistor has a collector connected to the voltage source, a base connected to the emitter of the third transistor, and an emitter connected to the current source, and the fourth transistor has a collector connected to the voltage source, a base connected to the emitter of the third transistor, and an emitter connected to the current source. The second transistor forms a differential pair with the second transistor; and the control terminal can selectively enable a desired one of the plurality of current ratio determining circuits.

A current dividing circuit according to another feature of the invention also comprises a current input terminal (12) for the current to be divided, a first and a second current output terminal (14, 16) and two control terminals (tS
).

a first transistor (Q1) whose collector is connected to the first current output terminal and whose emitter is connected to the current input terminal via a resistor (Rr); the collector is connected to the base of the first transistor; and further connected to the output of the current mirror circuit (20), the base of which is connected to the emitter of the first transistor,
a second transistor (Q2) whose emitter is connected to the current source (19); and a plurality of selectable current ratio determining circuits, each of which is connected to a third transistor (Q2);
Q3) and a fourth transistor (Q4), the third transistor has a collector connected to the second current output terminal and an emitter connected to the current input terminal via a current ratio determining resistor (R9). The fourth transistor has a collector connected to the input of the current mirror circuit, a base connected to the emitter of the third transistor, and an emitter connected to the current source. The second transistor and the second transistor form a differential pair, and a desired one of the plurality of current ratio determining circuits can be selectively enabled by the control terminal.

[Operation] In the current dividing circuit of the present invention configured as described above, a negative feedback loop is formed by the first and second transistors Ql, Q2, the selected fourth transistor, the current source 19, and RF/R. By setting the emitter of the first transistor Ql and the emitter of the selected third transistor Q3 to the same potential, the current ratio I + /I a
can be determined only by the value of the resistor, regardless of the transistor.

[Example 1] Examples of the present invention will be described below with reference to the drawings.

FIG. 1 shows a circuit diagram of a current dividing circuit which is an embodiment of the present invention.
A current input terminal 12, a first current output terminal 14, a second current output terminal 16, and a control terminal 18 for N to flow into.
Contains. The collector of the npn transistor Q1 is connected to the first current output terminal 14, through which the collector current 11 flows. The emitter of transistor Q1 is n p
It is connected to the base of the n-transistor Q2, and further connected to the current input terminal 12 via a resistor RF.

The collector of transistor Q2 is connected to the base of transistor Ql, and further connected from there through constant current source 17 to voltage source VCC. A resistor and a constant voltage source can be used instead of the constant current source 17 and the voltage source VccO, respectively. The emitter of transistor Q2 is grounded through constant current source 19. A resistor may be used instead of the constant current source 19. In this specification,
The term current source or constant current source shall also include resistors.

Block portions A, B, . . . surrounded by broken lines indicate a plurality of current ratio determining circuits, and any one current ratio determining circuit can be selected as described later. Current ratio determining circuit A
, B... are two npn transistors Q3A, Q3. ... and Q4, , Q4a...-. The collector of the transistor Q3 is connected to the second current output terminal 16, through which the collector current 3 flows. The emitter of transistor Q3 is connected to transistor Q4.
The transistor Q3 is connected to the base of the transistor Q1, and further connected to the current input terminal 12 via a current ratio determining resistor R, and the transistor Q3 forms an operational pair with the transistor Q1. Resistors R9A, Rsa... in each current ratio determining circuit are as follows:
Each can have a different resistance value. The collector of transistor Q4 is connected directly to voltage source Vee. Alternatively, the collectors of transistors Q4 and Q2 may be connected to the input and output of the current mirror circuit, respectively; for example, as schematically shown in FIG. Through Q5, the collector of transistor Q4 is input to transistor Q6, and each constant voltage source V c
It can be connected to c. The current mirror circuit is not limited to the embodiment shown in FIG. 2, but may be any type of circuit. The emitter of transistor Q4 is grounded through constant current source 19. Transistor Q2
and Q4 form a differential pair.

Control terminal 1 connected to the base of transistor Q3
8 may be a logic voltage input terminal providing a high level voltage or a low level voltage. Current ratio determining circuit A can be selected by turning on transistors Q3A and Q4A by setting control terminal 18A to a high level voltage and all other control terminals to low level voltage. Similarly, any one of the other control terminals 18B, 18G, . . . can be selected. A digital signal of several bits is received and converted into one selection signal by a decoder, so that one control terminal can be selected.

Typically, the voltage drop across R, is equal to the differential pair formed (Q
2/Q4) as a value sufficiently larger than the offset voltage of 0.
, about 3v. The collector-emitter voltage VCE of each transistor is 300 mV or more to avoid saturation, and therefore the operating voltage between the current input and output terminals is required to be 0.6V. Although all of the above transistors have been described as npn bipolar transistors, the invention is not limited to this; for example, pnp transistors or FETs can be used.

The operation will be explained below with reference to FIG.

FIG. 3 shows a circuit diagram equivalent to the current dividing circuit of FIG. 1 when any one of the plurality of current ratio determination circuits A, B, . . . is selected. To simplify the explanation of the operation, it is assumed that the current ratio determining circuit A is selected, and Q in FIG.
2. Q4A, 17.19 and V ce are 1 in Figure 3.
It is replaced with one operational amplifier.

That is, the emitter of the transistor Q1 is connected to the inverting input of the operational amplifier, and the emitter of the transistor Q3 is connected to the non-inverting input. The output of the operational amplifier is connected to the base of transistor Q1, forming a negative feedback loop. If the potential at node E falls below that at node F, the operational amplifier operates to raise the base potential of transistor Ql. Therefore, the potential at node E increases. Conversely, when the potential at node E becomes higher than node F, the operational amplifier lowers the base potential of transistor Q1, allowing Ql to move in the off direction. Therefore, the potential at node E decreases.

In this way, node E and node F are always kept at the same potential.

Therefore, the operational amplifier shown in FIG. 3 operates to satisfy the following equation.

I I XRF=I 3XR8 (4) That is,
In the conventional technology as shown in FIG.
, :: (3) Formula (7) l V Bts V 8E
The l 1 term can be divided by υt. From equations (2) and (4), the following equations are obtained.

I +=I+xXRs/Rs+Rr (511s=
I + N

[Effects of the Invention] Since the present invention is configured as described above, the current division ratio can be determined simply by the ratio of resistance values without depending on the size of the transistor, and great benefits can be obtained.

When the circuit of the present invention is implemented using an IC, it is easy to increase the accuracy of the resistance value, and a highly accurate current ratio can be obtained. During the IC manufacturing process, several resistance values R3 can be freely set with high precision, for example, by metal mask options. In an application example where IIN is fixed and IIN is controlled, IIN is set to 2 mA-15,75II.
It is possible to set several arbitrarily selected current values in steps of 0.5 mA within the range of IA.

As for the operating voltage, the voltage limit between input and output is the same as that of the conventional one, so there is no adverse effect.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a current dividing circuit which is an embodiment of the present invention. FIG. 2 is a partial circuit diagram illustrating a different embodiment of the supply voltage source to transistors Q2 and Q4 of FIG. FIG. 3 is an equivalent circuit diagram for explaining the operation of the circuit of FIG. 1. FIG. 4 is a circuit diagram illustrating a conventional current dividing circuit. FIG. 5 is a circuit diagram of a conventional current dividing circuit including a plurality of current ratio determining circuits. [Explanation of symbols 1 1O...Current dividing circuit, 12...Current input terminal 14
．． 16...first and second current output terminals 17...
Constant current source, Vcc...voltage source 18...control terminal,
20...Current mirror circuit Q1...First transistor Q2...Second transistor Q3...Third transistor Q4...Fourth transistor Transistor R...Resistor, R3...Resistor for determining current ratio Applicant: Motorola Inc. Patent attorney Susumu Ohnuki Masanori Honjo Figure 1 Figure 2

Claims (4)

[Claims] (1) Current input terminal (12) for the current to be divided: first and second current output terminals (14, 16); control terminal (18); collector connected to said first current output terminal; , a first transistor (Q1) whose emitter is connected to the current input terminal via a resistor (R_F); whose collector is connected to the base of the first transistor and which further supplies a voltage through a current source (17). a second transistor (Q2) connected to a current source (V_c_c), with a base connected to the emitter of said first transistor and an emitter connected to a current source (19); and a plurality of selectable current ratio determinations. circuit; each of the plurality of current ratio determining circuits includes a third transistor (
Q3) and a fourth transistor (Q4), the third transistor has a collector connected to the second current output terminal and an emitter connected to a current ratio determining resistor (R_s).
The fourth transistor has a collector connected to the voltage source, a base connected to the emitter of the third transistor, and an emitter connected to the current input terminal through the fourth transistor, and has a base connected to the control terminal. connected to a source to form a differential pair together with the second transistor; capable of selectively enabling a desired one of the plurality of current ratio determining circuits by the control terminal; current divider circuit. (2) Current input terminal (12) for the current to be divided: first and second current output terminals (14, 16); control terminal (18); collector connected to said first current output terminal; , a first transistor (Q1) whose emitter is connected to the current input terminal via a resistor (R_F); whose collector is connected to the base of the first transistor and further connected to the output of the current mirror circuit (20); connected, the base being connected to the emitter of the first transistor,
a second transistor (Q2) whose emitter is connected to the current source (19); and a plurality of selectable current ratio determination circuits; each of the plurality of current ratio determination circuits is connected to a third transistor (Q2);
Q3) and a fourth transistor (Q4), the third transistor has a collector connected to the second current output terminal and an emitter connected to a current ratio determining resistor (R_s).
The fourth transistor has a collector connected to the input of the current mirror circuit, a base connected to the emitter of the third transistor, and an emitter connected to the current input terminal via the fourth transistor. is connected to the current source to form a differential pair together with the second transistor; a desired one of the plurality of current ratio determining circuits can be selectively enabled by the control terminal; A current dividing circuit featuring: (3) The control terminal is a logic voltage input terminal, and selects any one current ratio determining circuit by turning on/off the third transistor and the fourth transistor; A current dividing circuit according to any one of the preceding claims. (4) The plurality of current ratio determining resistors each have a different resistance value, and different current ratios can be achieved by selecting different current ratio determining circuits; Current divider circuit described in .