JP3407819B2 - Current mirror circuit - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current mirror circuit capable of obtaining an output current of a predetermined magnification with high precision with respect to a reference current and realizing a high output resistance.

[0002]

2. Description of the Related Art A conventional current mirror circuit is shown in FIG. This circuit is of the Wilson type in which the accuracy of the output current with respect to the reference current is increased. Q1'-Q4 'is β
Bipolar npn having the same (grounded emitter type current amplification factor)
Type transistor, 1 is a reference current source, and 2 is an output terminal.

In this circuit, a current obtained by subtracting the collector current and the base current of the transistor Q1 'from the current Ir output from the reference current source 1 becomes the base current of the transistor Q2'. The base current of the transistor Q2 'is multiplied by β to become the output current Io, and also multiplied by β + 1 to become the emitter current. The current obtained by subtracting the collector current and the base current of the transistor Q3 'from the emitter current of the transistor Q2' is the transistor Q2 '.
4 ′ of the base current, and β of the base current
The doubled current becomes the collector current of the transistor Q4 ', that is, the emitter current of the transistor Q1'.

In this way, the current flowing through the output terminal 2 is detected by the transistor Q3 ', and the detection signal is input to the transistor Q4'.
The transistor Q1 'is subjected to negative feedback control by 4', and the collector current of the transistor Q2 'is stabilized.
A current substantially equal to the reference current Ir is obtained at the output terminal 2 as the output current Io.

Quantitatively, Io = Ir [1-2 / (β ² + 2β + 2)] (1), and when β is sufficiently large, Io≈Ir (2) In addition, the output resistance Ro is a transistor Q connected to r _{0 2.}
When the collector resistance of 2 ', the _{Ro ≒ β · r 0 2/} 2 ··· (3).

[0006]

FIG. 3 is a circuit diagram of a Wilson type current mirror circuit for obtaining an output current Io which is n times as large as the reference current Ir. Here, the emitter areas of the transistors Q2 ″ and Q3 ″ are set to n times the size of the transistors Q1 ′ and Q4 ′.
β and the like are the same for the transistors Q1 ′, Q2 ″, Q3 ″, Q4 ′.

The operating principle is similar to that of the circuit of FIG. 2, but the output current Io is

[0008] next, if where the n << β, Io ≒ nIr + (n + 1) Ir / β = nIr + (n + 1) becomes I _B ··· (5). I _B is the base current of transistor Q1 '.

As described above, in the circuit of FIG. 3, the reference current I
In addition to the output current “nIr” which is n times as large as r, a base current error amount of n + 1 times was generated, and the reference current could not be amplified with high accuracy.

The present invention has been made in view of the above points,
It is an object of the present invention to provide a current mirror circuit capable of highly accurate current conversion and having a high output resistance.

[0011]

An object of the present invention is to provide a first transistor through which a reference current flows, a second transistor for outputting a current corresponding to the output current of the first transistor to an output terminal, and the second transistor. In a Wilson type current mirror circuit comprising a third transistor for detecting the output current of the first transistor and a fourth transistor for inputting the output current signal detected by the third transistor to control the first transistor in negative feedback. A current characterized in that a fifth transistor is provided for inputting the output current signal detected by the third transistor and adding and outputting a current corresponding to the current for negative feedback controlling the first transistor to the output terminal. Achieved by a mirror circuit.

In the present invention, the output currents of the five transistors are preferably set by the size ratio of the fifth transistor to the first to fourth transistors.

Further, in the present invention, it is preferable to connect a level shift diode between the fifth transistor and the output terminal.

Further, in the present invention, all of the transistors used may be bipolar npn type transistors, bipolar pnp type transistors, n channel type field effect transistors or p channel type field effect transistors.

According to the present invention, a diode-connected first transistor to which a reference current is input, and a second transistor in which the first transistor and the base are commonly connected and the collector is connected to an output terminal
A transistor, a diode-connected third transistor through which an emitter current of the second transistor flows, and a fourth transistor in which the third transistor, the base, and the emitter are commonly connected, and the collector is connected to the emitter of the first transistor. In a Wilson type current mirror circuit in which the output current output from the second transistor is detected by the third transistor and is fed back to the first transistor by the fourth transistor, the third transistor, the base and the emitter are provided. Are commonly connected to each other, and a fifth transistor having a size that is a predetermined multiple of the first to fourth transistors is provided, and the collector of the fifth transistor is connected to the output terminal. Can be achieved.

Here, a diode having the same size as the fifth transistor can be connected between the collector of the fifth transistor and the output terminal.

[0017]

EXAMPLES Examples of the present invention will be described below. FIG. 1 is a circuit diagram showing a current mirror circuit of the embodiment. Q1 to Q4 are npn transistors (size n),
Q5 and Q6 are also npn transistors (size m).
Here, the transistor Q having the same configuration as that shown in FIG.
In the current mirror circuit including 1 to Q4, a transistor Q3, a transistor Q5 whose base and emitter are commonly connected, and a diode-connected transistor Q6 are connected in series and are connected between the output terminal 2 and the ground. .

In this embodiment, the transistors Q1 to Q4 are used.
Of the Wilson type current mirror circuit composed of
Output current Io1 generated in the collector of the transistor Q2
Depends on the basic operation of the Wilson current mirror circuit and the base current I _B5 of the transistor Q5.

Here, in FIG. 1, the transistor Q1
Current flowing through each part of-Q6 (subscript B, E, C is the base, emitter, the distinction of the collector, 1-6 shows the distinction between transistors Q1 to Q6.) _{Is, I B2 = Io 1 / β} I _{E2 = (β + 1) ·} I B2 = Io 1 · (β + 1) / β I E1 = I C4 = Ir-I B2 = Ir-Io 1 / β I B4 = I C4 / β = (Ir-Io 1 / β) _{/ β I E4 = I B4 ·} (1 + β) = (Ir-Io 1 / β) (1 + β) / β = I E3 I B5 = I B4 · m / n I C5 = I C4 · m / n = m / n (Ir-Io ₁ / β).

Therefore, if β is sufficiently large, the output current Io ₁ becomes Io ₁ ≉Ir + (m / n) (Ir / β) (6)

On the other hand, since the collector current I _C5 generated in the transistor Q5 is similar to the collector current I _C4 of the transistor Q4, as described above, I _C5 = I _C4 (m / n) = (Ir-Io ₁ / Β) (m / n), the output current Io ₂ generated here is If β is sufficiently large, Io ₂ ≈ (m / n) [Ir− (Ir / β)] (8)

Therefore, the output current Io is calculated from the equations (6) and (7) as follows: Becomes If β is sufficiently large, Io≈Ir [1+ (m / n)] (10).

That is, by generating and adding the currents represented by the equations (7) and (9), the output represented by the equation (11) in which (Ir / β) included in both equations is canceled. The current Io can be obtained. This output current Io
Does not affect the elements of the transistors Q1 to Q6, and an output current according to the size ratio (m / n) can be accurately obtained.

Next, the output resistance Ro is the output resistance Ro ₁ on the side where the current Io ₁ flows and the output resistance R on the side where the current Io ₂ flows.
It is a parallel connection value of o ₂ . First, the output resistance Ro ₁ on the side where the current Io ₁ flows is Ro ₁ ≈ (β / 2) r _o2 (11). r _o2 is the collector resistance of the transistor Q2.

On the other hand, on the side of the current Io _2, the variation amount ΔI _C5 of the collector current I _C5 of the transistor Q5 appears as −ΔI _{C5 in} the base current of the transistor Q5, and becomes −αΔI _C5 through the transistor Q2. It returns to the 2 side (α is the base ground current amplification factor).

Therefore, the fluctuation ΔI of the output current Io generated from the output current Io ₂ due to the fluctuation of the output voltage of the output terminal 2
o is substantially ΔIo = ΔI _C5 −αΔI _C5 = (1−α) ΔI _C5 (12) If α≈1, then ΔIo≈0. Quantitatively, from r _{0 5} · ΔI _C5 = Ro ₂ (1-α) ΔI _C5 (13) (r _{0 5} is the collector resistance of the transistor Q ₅ ), Ro ₂ = r _{0 5} / (1- α) = (1 + β) r _{0 5} (14)

Therefore, the total output resistance Ro is _ro2
= R ₀ , r _{0 5 ≈r o2} (n / m) = r ₀ (n /
From _{m), Ro = Ro 1 //} Ro 2 = (β · r 0/2) // [(1 + β) (n / m) r 0 = {(β 2 + β) n / [(2n + m) β + 2n]} r ₀ (15), which is a high value depending on β.

Next, the transistor Q6 is diode-connected to the collector of the transistor Q5. This is because the transistor Q4
And the transistor Q5 keep the same bias.
That is, when the output terminal 2 is in a biased state of 2V _BE (V _BE is the voltage between the base and emitter of the transistor), the transistor Q6 is inserted so that the transistor Q6
4 and transistor Q5 have the same V _CE (collector-emitter voltage), and these two transistors Q4, Q
Keep β in 5 in the same state.

With such a configuration, the reference current Ir
It is possible to generate an output current Io having a very small error. The magnification of this current Io can be selected according to the size ratio (m / n) of the transistors.
Further, a current source circuit or the like having a high value output resistance can be realized.

[0030]

As described above, according to the present invention, it is possible to accurately amplify a current and to have a high output resistance. Therefore, there is an advantage that it can be applied to a constant current source such as an A / D or D / A converter that requires high accuracy and an application to amplify a small signal current.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a current mirror circuit according to an embodiment of the present invention.

FIG. 2 is a circuit diagram of a conventional Wilson current mirror circuit.

FIG. 3 is a circuit diagram of a conventional Wilson type current mirror circuit.

Claims (6)

(57) [Claims] 1. A first transistor through which a reference current flows, a second transistor for outputting a current corresponding to an output current of the first transistor to an output terminal, and a third transistor for detecting an output current of the second transistor. A Wilson type current mirror circuit comprising a fourth transistor for inputting an output current signal detected by the third transistor and performing negative feedback control of the first transistor, wherein the output current detected by the third transistor is A current mirror circuit comprising a fifth transistor for inputting a signal and adding and outputting to the output terminal a current corresponding to a current for negative feedback controlling the first transistor. 2. The current mirror circuit according to claim 1, wherein the output current of the five transistors is set by the size ratio of the fifth transistor to the first to fourth transistors. 3. The current mirror circuit according to claim 1, further comprising a level shift diode connected between the fifth transistor and the output terminal. 4. A bipolar npn-type transistor, a bipolar pnp-type transistor, an n-channel type field effect transistor, or a p-channel type field effect transistor as all of the transistors used. The current mirror circuit described in the item. 5. A first diode connection for inputting a reference current.
A transistor, a second transistor having the first transistor and the base commonly connected and a collector connected to the output terminal, a diode-connected third transistor through which an emitter current of the second transistor flows, the third transistor and the base, A fourth transistor having emitters commonly connected to each other and a collector connected to an emitter of the first transistor, the output current output from the second transistor is detected by the third transistor, and the first current is detected by the fourth transistor. In a Wilson type current mirror circuit configured to feed back to a transistor, a third transistor, a base and an emitter are commonly connected to each other, and a fifth transistor having a size that is a predetermined multiple of the first to fourth transistors is provided, The collector of the fifth transistor is the above A current mirror circuit characterized by being connected to the output terminal. 6. The current mirror circuit according to claim 5, wherein a diode having the same size as that of the fifth transistor is connected between the collector of the fifth transistor and the output terminal.