JPH0151208B2 - - Google Patents

Description

[Detailed description of the invention] [Technical field to which the invention pertains] The present invention relates to voltage-to-current conversion amplifiers.

[Prior art]

In addition to the conventional voltage-to-current conversion amplifier (hereinafter referred to as GM amplifier) that uses an operational amplifier, a relatively simple one having the configuration shown in FIG. 1 is well known. In the figure, V ⁺ is a positive power supply terminal, V ^- is a negative power supply terminal, and 1 to 4 are constant current sources that take the same value. IN ₁ and IN ₂ are voltage input terminals, OUT ₁ and
OUT ₂ is the current output terminal, and Q ₁ ′ and Q ₂ ′ are PNP transistors for the GM amplifier. The transconductance GM ₁ of this circuit is expressed as follows.

GM ₁ = α/R _E +2γ _e ……(1) Here, R _E is the resistance γ _e inserted between the collectors of Q ₁ ′ and Q ₂ ′ is the dynamic emitter of transistors Q ₁ ′ and Q ₂ ′. Assuming that the current of the constant current sources 1 to 4 using the resistor is I ₀ and the common base current amplification factor of the transistor is α, it is given by the following equation.

γ _e =α·kT/qI ₀ ...(2) where k is the Boltzmann constant, q is the electron charge, and T is the absolute temperature. Also, constant current sources 1 to 4
must be the same value in order to achieve balance, that is, to make the output offset zero.
As a method for realizing this, for example, as shown in FIG. 2, there is a configuration using current mirrors CM ₁ ' and CM ₂ '. In the figure, 6' and 7' are discharge type constant current output terminals, 9' and 10' are suction type constant current output terminals,
5' and 8' are reference current input terminals that serve as a reference for the constant current output of each current mirror. This reference current I _ref is connected to the Darlington connected transistor Q ₃ ′,
Transistor driven by Q ₄ ′ and reference power supply V′ _B1
The reference current I _ref is obtained from a circuit consisting of Q ₅ ' and an inserted resistor R' _I , and the base-emitter voltage of the transistor is expressed as V _BE .

I _ref = |V′ _B1 |−3V _BE /R′ _I ……(3) Assuming that the input/output current ratio of both current mirrors CM ₁ ′ and CM ₂ ′ is 1, the transistor for GM amplifier
In order to balance Q ₁ ′ and Q ₂ ′, that is, GM
In order to make the output current zero when the amplifier input voltage is zero, the input terminal 5' of the current mirror CM ₁ ' is connected as follows.
The input terminal 8' of the current mirror CM ₂ ' is connected to the input terminal 8' of the current mirror CM ₂ ' via the NPN Darlington connected transistors Q3' and _Q4 '.
I _ref is transmitted through the PNP transistor Q ₅ '. That is, the error in the base currents of transistors Q ₁ ′ and Q _{2 ′} is compensated for by the base current of transistor Q ₅ ′. This configuration certainly compensates for the base current error as far as the GM amplifier's DC bias is concerned, but it does not compensate for the AC error at all. That is, from an AC point of view, the transfer conductance GM ₁ of this GM amplifier deviates from the ideal value 1/R _E +2γ _e depending on α, as shown in equation (1). This error is usually 0.25% to 1
%, which poses a problem in applications that require high accuracy.

[Purpose of the invention]

A first object of the present invention is to provide a voltage-current amplifier in which not only the DC bias but also the error caused by α in the AC characteristics are extremely reduced by eliminating the above-mentioned drawbacks.

In addition to the first object, a second object of the present invention is to provide a voltage-current conversion amplifier having good high frequency characteristics.

[Structure of the invention]

The voltage-current conversion amplifier of the first invention includes a first Darlington-connected transistor whose base is connected to a first input terminal and whose output collector is connected to the first output terminal;
A second Darlington connection transistor connected to the output terminal, a resistor connected between the output emitters of the first and second Darlington connection transistors, and a reference current that is the same as that of the first and second Darlington connection transistors. a third Darlington connection transistor of conductivity type and a fourth Darlington connection transistor of opposite conductivity type, and supplying a bias current to the output emitter and output collector of the first and second Darlington connection transistors, respectively; and a second current mirror.

The voltage-current conversion amplifier of the second invention includes a first Darlington-connected transistor whose base is connected to a first input terminal and whose output collector is connected to the first output terminal;
A second Darlington connection transistor connected to the output terminal, a resistor connected between the output emitters of the first and second Darlington connection transistors, and a reference current that is the same as that of the first and second Darlington connection transistors. a third Darlington connection transistor of conductivity type and a fourth Darlington connection transistor of opposite conductivity type, and supplying a bias current to the output emitter and output collector of the first and second Darlington connection transistors, respectively; and a second current mirror, and idling current supply means for supplying idling current to the output transistors of the first, second, and third Darlington connection transistors.

[Explanation of Examples]

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

FIG. 3 is a circuit diagram of an embodiment of the first invention.

In this embodiment, the base is connected to the first input terminal IN ₁ and the output collector is connected to the first output terminal OUT ₁ .
Darlington connected PNP transistors Q ₂ , Q ₈
, second Darlington-connected PNP transistors Q ₁ , Q ₇ whose bases are connected to the second input terminal IN ₂ and whose output collectors are connected to the second output terminal OUT ₂ , and first and second Darlington-connected transistors Q ₂ , Q ₈ , Q ₁ ,
A resistor R _E connected between the output collector of Q ₇ and a reference current I _ref are connected to a third Darlington connection having the same conductivity type as the first and second Darlington connection transistors Q ₂ , Q ₈ , Q ₁ , and Q ₇ PNP transistors Q ₅ and Q ₆ and a fourth Darlington-connected NPN transistor of opposite conductivity type
The bias current is supplied through Q ₃ and Q ₄ to the first and second Darlington connected transistors, respectively.
First and second current mirrors supplying the output emitters and output collectors of Q ₂ , Q ₈ , Q ₁ , and Q ₇
It consists of CM ₁ and CM ₂ . In addition, in the same figure
V _B1 is the reference power supply, V ⁺ is the positive power supply terminal, and V ^- is the negative power supply terminal.

That is, the difference between the circuit of this embodiment and the conventional circuit shown in FIG. 2 is that the GM amplifier transistors Q ₁ ′ and Q ₂ ′ and the reference current generation transistor Q ₅ ′ in FIG. The reason is that it is a connected transistor.

As is well known, when a Darlington connected transistor is composed of two transistors as shown in FIG. 3, assuming that the two transistors have the same _α0 ,
The total α _T is given by α _T =1−(1−α ₀ ) ² ……(4). Now, if α ₀ =0.99 (h _fe =100), then α _T =0.9999, and as can be seen from equation (1), the error due to α in the AC characteristics is 0.01%. Therefore, the error caused by α in the DC bias and AC characteristics according to this embodiment can be extremely small to about 0.01% at worst.

However, according to this embodiment, this GM amplifier has first and second Darlington connection transistors Q ₂ ,
The emitter currents of the input side transistors Q _{8 and} Q ₇ of Q 8 , Q 1 and Q ₇ are equal to the base currents of the output side transistors Q ₂ and Q ₁ , so the operating current of the transistors Q _{8 and} Q ₇ becomes very small. As a result, the high frequency characteristics of the GM amplifier may be impaired.

FIG. 4 is a circuit diagram showing a first embodiment of the second invention.

In the circuit of this embodiment, a third current mirror CM ₃ driven by an idling reference current I _b is added to the circuit of the embodiment of the first invention shown in FIG. 3, and its constant current output terminal 12, 13 and 14 are connected to the emitters of transistors Q ₇ , Q ₈ , and Q ₆ , respectively, so that idling current can be supplied to transistors Q ₇ , Q ₈ , and Q ₆ .

Therefore, according to this embodiment, the transistors Q ₇ ,
_Q8 is supplied with idling current by a separate circuit, improving its high frequency operation. Furthermore, since idling current is similarly supplied to transistor _Q6 , the balance of the GM amplifier is maintained sufficiently.

FIG. 5 is a circuit diagram of a second embodiment of the second invention.

In the circuit of this embodiment, instead of the third current mirror CM ₃ in the first embodiment shown in FIG.
The current mirror output of the first current mirror CM ₁ in the embodiment of the first invention shown _in FIG _. , _Q8 . Therefore, as in the first embodiment, it is possible to improve the high frequency characteristics and maintain the balance of the GM amplifier.

By the way, in the first embodiment, the third
The current mirror CM ₃ also requires precision in the transmission ratio of the current mirror, so _there is a risk that the circuit scale will become slightly large. CM ₄ terminal 5, terminal 13 transistor
Since a negative feedback loop L ₁ is created that reaches the base of Q ₅ ,
It is necessary to design the loop gain to be 1 or less.

FIG. 6 is a circuit diagram showing a third embodiment of the second invention.

The _circuit of this embodiment is based on the circuit of the embodiment _of the first invention shown in FIG _. As idling current supply means, a resistor R _P is inserted between the base and emitter of the output transistors Q ₂ , Q ₁ , and Q ₅ .

In this case, the idling current I _id is the base-emitter voltage V _BE of transistors Q ₁ , Q ₂ , Q ₅ (approximately 0.7 volts for silicon transistors), I _id = V _BE /R _P ……(5 ) is given by

Therefore, by selecting the value of the resistor R _P so as to obtain desired high frequency characteristics, the high frequency characteristics can be improved and the balance of the GM amplifier can be maintained.

Furthermore, if the shapes of the first, second, and third Darlington connection transistors are made the same and the value of the resistor R _P is selected to be the same, a well-balanced DC and AC with no errors and good high frequency characteristics can be obtained. You can get a GM amplifier. Moreover, it goes without saying that it is well balanced with respect to temperature fluctuations. Furthermore, since there is no closed loop, there is no fear of oscillation, and the number of elements can be reduced.

Note that in this embodiment, the same effect can be obtained even if the resistor R _P is replaced with a suitable diode.

Furthermore, in the above embodiments, a case has been described in which the Darlington connection transistor is composed of two transistors, but the number of transistors may be increased depending on the required accuracy.

Furthermore, in the circuit configuration described above, it goes without saying that the present invention is applicable even if the conductivity types of the transistors are reversed.

〔Effect of the invention〕

As explained above in detail, the voltage-current conversion amplifier of the present invention has a Darlington connection transistor as a voltage-current conversion transistor and a transistor of a current mirror reference current generation circuit, so errors due to DC bias and α of AC characteristics It has the effect that it is extremely small. Furthermore, by adding means for supplying idling current to the input side transistor of the Darlington connected transistor, it is possible to obtain good high frequency characteristics.

[Brief explanation of drawings]

1 and 2 are circuit diagrams showing an example of a conventional voltage-current amplifier, FIG. 3 is a circuit diagram of an embodiment of the first invention, and FIGS. 4, 5, and 6 are circuit diagrams showing an example of a conventional voltage-current amplifier. They are circuit diagrams of first, second, and third embodiments of the second invention, respectively. 1 to 4...constant current source, 5, 5', 6, 6', 7,
7', 8, 8', 9, 9', 10, 10', 11, 1
2, 12', 13, 13', 14, 14'... Output terminal of Kale mirror, Q ₁ , Q ₁ ', Q ₂ , Q ₂ '... PNP
Transistor, Q ₃ , Q ₃ ′, Q ₄ , Q ₄ ′...NPN transistor, Q ₅ , Q ₅ ′, Q ₆ , Q ₇ , Q ₈ ...PNP transistor, CM ₁ , CM ₁ ′, CM ₂ , CM ₂ ′, CM ₃ ……
Current mirror, R _E , R _I , R′ _I , R _P ...resistance,
V _B1 , V′ _B1 ...Reference power supply, V ⁺ ...Positive power supply terminal,
V ^- ... Negative power supply terminal, I _ref , I _b ... Reference current, IN ₁ ,
IN ₂ ... Voltage input terminal, OUT ₁ , OUT ₂ ... Current output terminal, L ₁ ... Negative feedback loop.

Claims (1)

[Claims] 1. The base is the first input terminal and the output collector is the first
a first Darlington connection transistor connected to an output terminal; a second Darlington connection transistor having a base connected to a second input terminal and an output collector connected to a second output terminal; and the first and second Darlington connection transistors. A reference current is supplied through a resistor connected between the output emitters of the transistor and a third Darlington transistor of the same conductivity type as the first and second Darlington transistors, and a fourth Darlington transistor of the opposite conductivity type. and first and second current mirrors for supplying bias currents to output emitters and output collectors of the first and second Darlington connected transistors, respectively. 2 The base is the first input terminal and the output collector is the first
a first Darlington connection transistor connected to an output terminal; a second Darlington connection transistor having a base connected to a second input terminal and an output collector connected to a second output terminal; and the first and second Darlington connection transistors. A reference current is supplied through a resistor connected between the output emitters of the transistor and a third Darlington transistor of the same conductivity type as the first and second Darlington transistors, and a fourth Darlington transistor of the opposite conductivity type. first and second current mirrors that supply bias currents to output emitters and output collectors of the first and second Darlington connected transistors, respectively; and input sides of the first, second and third Darlington connected transistors. and idling current supply means for supplying idling current to a transistor. 3. Idling current supply means for supplying idling current to the input side transistors of the first, second and third Darlington connection transistors through an idling current output terminal provided on the third current mirror or the first current mirror. A voltage-current conversion amplifier according to claim 2. 4. The voltage-current converter according to claim 2, wherein the idling current supply means comprises a resistor or diode inserted between the base and emitter of the output side transistor of the first, second, and third Darlington connection transistors. amplifier.