JPH05335847A - Current mirror circuit - Google Patents

Abstract

PURPOSE:To obtain the current mirror circuit keeping a high output impedance and suppressing nonlinear distortion. CONSTITUTION:A 4th transistor (TR) Q4 is in cascade-connection to a 3rd TR Q3 being an output TR of a feedback type current mirror circuit and a constant voltage source VCONST is connected between a base of the 4th TRQ4 and an emitter of the 3rd TR Q3. Thus, a collector-emitter voltage of the 3rd TRQ3 is fixed to eliminate the effect of Early effect and a change in a collector-base capacitance thereby reducing nonlinear distortion of the output current.

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 used in various amplifier circuits.

[0002]

2. Description of the Related Art A current mirror circuit is known as a basic circuit of a bipolar transistor. A basic current mirror circuit allows a reference input current to flow through the collector side of a diode-connected transistor by short-circuiting the collector and base, and the short-circuit connection point of the collector-base is placed in close proximity to other equivalent characteristics. It consists of a circuit that connects to the base of a transistor.

The above-mentioned basic current mirror circuit theoretically operates with a correct mirror coefficient, but actually has a problem that the output current fluctuates due to the effect of the Early effect. The Early effect means that when the collector-emitter voltage V _CE of the transistor increases, the depletion layer expands due to a decrease in electron concentration and the effective base width narrows, and the collector current tends to increase as the collector voltage increases. It is a phenomenon that becomes.

A feedback current mirror circuit as shown in FIG. 5 is known as a highly accurate current mirror circuit for suppressing the fluctuation of the output current due to the influence of the Early effect. The current mirror circuit, the base and the Wilson current mirror circuit, the transistor Q ₄ of a pnp common base cascode connected to the output transistor Q ₃ of the pnp type, between the base and the transistor Q ₂ of the transistor Q ₄ emitters _Is connected to a constant voltage source V _CONST and is often used in an audio amplifier circuit. Thus, the transistor Q ₄ and the constant voltage source V
By connecting _CONST , the constant voltage of the constant voltage source V _{CONST and} the constant value of the base-emitter voltage V _BE (≈0.6 V) of the transistor Q ₄ and the transistor Q _{2 make} the collector-emitter voltage V of the transistor Q ₃ By clamping the fluctuation of _CE3, the fluctuation of the output current due to the Early effect is suppressed.

[0005]

However, in FIG.
The current mirror circuit shown is a transistor Q with a grounded base.
_FourHigh output impedance due to
, But its input / output characteristics are linear.
Not always enough in terms. This non-linear distortion is
This is a serious problem especially in audio circuits.

That is, in the current mirror circuit of FIG. 5, the forward voltage drop V _F of the diode-connected transistor Q ₂ and the base-emitter voltage V _{BE4 of the} transistor Q ₄ are substantially constant (≈0.6 V). Therefore, the collector potential V _c of the transistor Q ₃ tends to be clamped by the constant bias voltage provided by the constant voltage source V _CONST . However, strictly speaking, the base-emitter voltage V _BE is not constant and generally depends on the output current and the emitter current I as expressed by V _BE = (kT / g) hm ( _IE / I _S ). It becomes non-linear with respect to _E. Here, k is the Boltzmann constant, T is the absolute temperature of the junction, q is the electron charge, and I _S is the reverse saturation current. The same applies to the forward voltage drop V _F of the transistor Q ₂ because it is diode-connected.

The change in the output current I ₂ following the change in the input current I ₁ is expressed as the change in the forward voltage drop V _F of the transistor Q ₂ as a diode and the change in the base-emitter voltage V _BE4 of the transistor Q _4. The change in the forward voltage drop V _F appears as a change in the collector-emitter voltage V _CE3 of the output transistor Q ₃ .
This change in V _CE3 causes a slight change in the output current due to the aforementioned Early effect, and the change in the capacitance C _ob due to the depletion layer between the PN junctions between the base and collector of the output transistor Q ₃ changes the output current, that is, The frequency characteristic varies depending on the amplitude of the output signal, and the distortion increases.

The distortion due to the Early effect will be described with reference to FIG. Figure 6 shows the V _CE -I _C characteristic that the base current i _B1 through i _B5 of the transistor Q ₃ as a parameter. Each curve does not have a flat characteristic due to the Early effect, and the collector current I _C3 of the transistor Q ₃ changes by 2ΔV _BE (≈ΔV _F + ΔV _BE4 ) as the output current I ₂ changes.
It changes by a minute, that is, 2 · ΔI _C3 . This change distorts the amplified waveform and is treated as a problem of deterioration of linearity of the amplifier circuit.

An object of the present invention is to provide a current mirror circuit capable of suppressing nonlinear distortion while maintaining high output impedance.

[0010]

[Means for Solving the Problems] To solve the above problems
According to the present invention, as shown in FIG.₁But
Input first transistor Q₁And the base is
First transistor Q ₁Daio connected to the base of
Connected second transistor Q₂And the base is the first
Transistor Q₁The emitter is connected to the collector of the front
Note 2nd transistor Q₂Connected to the collector of
Second transistor Q₂Output current I₁To
Third transistor Q taken out₃And
In the error circuit, the third transistor Q₃To the fourth
Transistor Q_FourCascode connection to this 4th
Langista Q_FourThe base of the third transistor and the third transistor
Mitter Q₃Constant voltage source V between_CONSTThat you have connected
Characterize.

[0011]

According to the present invention, connecting a constant voltage source V _CONST between the fourth base of the transistor Q ₄ which is connected to the third emitter of the transistor Q ₃ to the third collector of the transistor Q _{3 Therefore} , the collector-emitter voltage V _{CE3 of} the third transistor Q ₃ is clamped. As a result, the collector-emitter voltage V _CE3 of the third transistor Q ₃ is the forward voltage drop V ₂ of the second transistor Q ₂ caused by the change of the output current I ₂ following the change of the input current I _{1. Since} it is not affected by the fluctuation of _F , the influence of the Early effect and the fluctuation of the PN junction capacitance C _ob (see FIG. 5) between the collector and the base of the third transistor Q ₃ are reduced, and the output current I ₂ is reduced. It is possible to reduce the included nonlinear component.

As described above, the high output impedance can be secured by the fourth transistor Q ₄ whose base is grounded, and the nonlinear distortion by the constant voltage source V _CONST can be reduced.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, preferred embodiments of the present invention will be described with reference to the drawings. [I] First Embodiment FIG. 2 shows a first embodiment of the present invention.

In the circuit shown in FIG. 2, a circuit A represents a voltage / current conversion circuit for converting an input voltage into a current. In this voltage / current conversion circuit A, the drain of the n-type field effect transistor Q ₅ is connected to the collector of the transistor Q ₁ , the source is grounded to the GND via the source resistance R _S , and the gate is connected to the GND. The gate resistance R _g is connected. The input signal is given to the gate of the transistor Q ₅ via the input terminal IN. Transistor Q ₅
Is the input current I ₁ that corresponds to the input signal voltage.
Is given to the transistor Q ₁ .

Circuit B is a conventional Wilson type circuit shown in FIG.
It has the same circuit configuration as the current mirror circuit, and
Register Q₁, Diode-connected feedback transistor
Q ₂, Output transistor Q₃, And cascode tiger
Register Q_FourConsists of.

2 is different from FIG. 5 (conventional circuit) in that the constant voltage source V _CONST is connected to the connection point between the emitter of the transistor Q _{3 and} the collector of the transistor Q ₂ , that is, between the node N ₂ and the transistor Q ₄ . A constant voltage source V _CONST is connected to a node N ₄ connected to the base, and a constant current source I _CONST is connected to the constant voltage source V _CONST to attract a constant current to generate a constant voltage at the constant voltage source V _CONST. That is the point. As the constant voltage source V _CONST , for example, a constant voltage diode such as a Zener diode is used, and the constant current source I
_{As the CONST} , for example, a constant current diode is used.

[0017] The collector of the transistor Q ₄ is grounded to GND via a load resistor R _L, the load resistance R _L
Node N _{3 at} the connection point between the transistor and the collector of the transistor Q ₄
The output signal voltage is taken out from the output terminal OUT.

Next, the operation will be described. When an input signal is applied to the input terminal IN, the input signal voltage is converted into a corresponding current by the voltage / current conversion circuit A, and the input current I
_The output current I ₂ depending on ₁ is V _CC → Q ₂ → Q ₃ → Q ₄ →
It flows in the route of _RL → GND. The magnitude of the output current I ₂ changes following the change of the input current I ₁ , and the output voltage corresponding to the change is taken out from the node N ₃ of the load resistance R _L via the output terminal OUT. become.

At this time, an output that follows changes in the input signal
Current I₂Changes the transistor Q₂Forward voltage of
Descent V_FFluctuates, but transistor Q₃Collector of
Emitter voltage V_CE3Is V_FTo be affected by fluctuations in
No change, transistor Q_FourBetween base and emitter
Voltage V_BE4It is only the fluctuation of. Therefore, V_CEStrange
I by movement_C3The fluctuation of ΔV_BE4To
ΔI of the corresponding part only _C3And the effect of the early effect and
Capacity C_obOf the output current I ₂Insidious
The linear waveform is reduced compared to the conventional one.

The constant voltage source V _CONST and the constant current source I
_{Since the} constant voltage is generated by the combination with _CONST ,
The output current I ₂ is smaller than the current I ′ ₁ flowing through the transistor Q ₂ by the amount of current shunting to the constant voltage source V _CONST side (I ₂ = I ′ ₁ −I ₃ ), but this current is a DC bias component. The change amount ΔI ₂ (signal amount) of the current as an AC component does not change, and the AC mirror operates as a current mirror circuit, so that the gain does not decrease. [II] Second Embodiment FIG. 3 shows a second embodiment of the present invention. This example
An example in which a push-pull amplifier circuit is configured using the current mirror circuit shown in FIG. 2 will be disclosed.

That is, as shown in FIG. 3, the current mirror circuits 1A and 1B according to the present invention are vertically symmetrically arranged. The transistors q ₁ to q ₄ constituting the upper current mirror circuit. 1B, Q ₁ to Q ₄ order to provide the symmetry of operation of the lower side of the current mirror circuit 1A
And npn type transistors. The transistor q _{5 is} also a p-type FET for the same reason.

Each of the current mirror circuits 1A and 1B operates in the same manner as the circuit shown in FIG. 2, suppresses even-order distortion of the waveform to be amplified, and constitutes an amplifier circuit with good linearity. [III] Third Embodiment FIG. 4 shows a third embodiment of the present invention. This example
A further specific example of the current mirror circuit shown in FIG. 3 will be disclosed.

As shown in FIG. 4, the current mirror circuit according to the present invention is applied to the drive circuit 100 placed before the power amplifier circuit 200. Drive circuit 1
Reference numeral 00 denotes a push-pull amplifier circuit configuration similar to the second embodiment shown in FIG. 3, and includes a DC servo circuit 3. The DC servo circuit 3 is a circuit for removing a DC offset generated at the output end OUT of the drive circuit 100 by feedback. That is, the DC servo circuit 3 has an n-type field effect transistor T ₁ and a p-type field effect transistor T ₂ which serve as a constant current source I _{CO NST,} and the gates of these transistors T ₁ and T ₂ are resistive. r ₁ and the capacitor C are connected. Resistance r ₁
Is connected to the output terminal OUT of the drive circuit 100, and the other end of the capacitor C is grounded to GND.
Integrator circuit (or low-pass filter) with this r ₁ and C
Is formed, the AC component generated at the output end OUT is removed, and only the DC component is fed back. r ₂ is a variable resistor for adjusting the DC offset voltage, both ends of which are connected to the sources of the transistors T ₁ and T ₂ , respectively, and the middle point is GN via the resistor r _3.
It is grounded to D. The DC offset component generated at the output terminal OUT passes through the resistor r ₁ and the transistors T ₁ and T ₂
Is suppressed by controlling the drain currents of the transistors T ₁ and T ₂ , that is, the ratios of the constant currents flowing to the upper and lower constant voltage sources V _CONST , respectively, according to the amount of the DC offset. become.

As described above, according to this embodiment, the current mirror circuit having a high output impedance and a low distortion and good linearity can be applied to a practical circuit, and the DC servo circuit 3 capable of removing the DC offset is used. They can be combined as a part to form an amplifier circuit with excellent characteristics.

[0025]

As described above, according to the present invention, the collector-emitter voltage of the third transistor forming the output transistor is fixed by the constant voltage source. Since the change in the capacitance between the bases can be suppressed, the linearity of the output signal can be improved.

[Brief description of drawings]

FIG. 1 is a diagram illustrating the principle of a current mirror circuit of the present invention.

FIG. 2 is a circuit diagram showing a first embodiment of a current mirror circuit of the present invention.

FIG. 3 is a circuit diagram showing a second embodiment of the current mirror circuit of the present invention.

FIG. 4 is a circuit diagram showing a third embodiment of the current mirror circuit of the present invention.

FIG. 5 is a circuit diagram of a conventional feedback type current mirror circuit.

FIG. 6 shows V _CE − of a current mirror circuit output transistor
It is a characteristic view which shows I _C characteristic.

[Explanation of symbols]

1, 1A, 1B ... current mirror circuit 2, 2A, 2B ... input circuit 100 ... drive circuit 200 ... power amplifier circuit A ... voltage / current conversion circuit B ... Wilson current mirror circuit Q _1, Q ₂ ~Q ₅ ... transistor q _1, q ₂ ~q ₅ ... transistor V _CONST ... constant voltage source I _CONST ... constant current source _{N 1, N 2, N 3} ... node IN ... input terminal OUT ... output terminal C _ob ... collector-base junction capacitance M … Master side S… Slave side V _CC … High potential side power source V _EE … Low potential side power source

Claims (1)

[Claims] 1. A first transistor to which a reference input current is input, a diode-connected second transistor whose base is connected to the base of the first transistor, and a base to the collector of the first transistor. A third transistor having a connected emitter whose collector is connected to the collector of the second transistor and which is connected in series to the second transistor to extract an output current; and A current mirror circuit in which a transistor is cascode-connected, and a constant voltage source is connected between the base of the fourth transistor and the emitter of the third transistor.