JP2596125Y2 - Operational amplifier circuit - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an operational amplifier circuit, and more particularly to an operational amplifier circuit for setting a gain by a resistance ratio.

[0002]

2. Description of the Related Art FIG. 5 is a circuit diagram of an example of a conventional operational amplifier circuit. In the figure, input terminals Va and Vb are input to input terminals 1 and 2, respectively, and an output current I _OUT corresponding to a voltage difference between the input voltages Va and Vb is connected to a resistor Rs connected between terminals 5 and 7. The output voltage V _OUT is output to the output terminal 7 after being amplified by the inverting amplifier 8 serving as amplifying means. The inverting amplifier 8, the voltage source E ₁ as a reference for the output voltage V _OUT is connected.

[0003] In FIG. 4, first and second input voltages V
a and Vb are input to the bases of the first and second transistors Q ₁ and Q _{2 having} the same characteristics, respectively, and the emitters of the transistors Q ₁ and Q ₂ are connected through terminals 3 and 4, respectively. Rg
Connected to both ends. Therefore, the voltage across the resistor Rg, which is the first resistor, is lower than the input voltages Va and Vb by the base-emitter voltage. The transistors Q ₃ and Q ₆ constituting the current detecting means, the transistors Q ₄ and Q ₅ , and the current mirror pair transistors Q ₇ and Q ₈ constituting the current generating means have the same characteristics.

[0004] For example, Va> if Vb, the emitter voltage of the transistor Q ₁ is than the emitter voltage of the transistor Q ₂ becomes higher by (Va-Vb), as shown in the resistance Rg (Va-Vb) / Rg Current ΔI flows. Therefore, increased collector current Ia of the transistor Q ₄ is, the collector current of the transistor Q ₅ is reduced, the transistor Q _3, Q ₄ Nobesu current Ic increases, transistor Q _5, Q ₆ Nobesu current Id decreases.

Accordingly, the collector current of the transistor Q ₃ to be supplied to the transistor Q ₇ as a reference current for the current mirror pair transistors Q _7, Q ₈ (1/2)
Ia increases and the collector current of transistor Q ₆ (1/1)
2) Ib decreases. The collector of the transistor Q ₈ is, (1/2) Ia becomes current is output. As a result,
The output current I _0UT (= ΔI) flows from the terminal 5 to the collector of the transistor Q ₈ via the resistor Rs as shown.

If Va = Vb, then Ia = Ib, so that _I.sub.0UT = 0. If Va <Vb, the output current _I.sub.0UT is applied to an output load (not shown) from the output terminal 7 via the resistor Rs. Flow in. The gain of the operational amplifier circuit 10 obtained at the output terminal 7 is configured so that G = K (Rs / Rg) (1). The operational amplifier circuit 10 is implemented as a semiconductor, and the resistors Rs and Rg are external resistors.

[0007]

However, in the above-mentioned conventional operational amplifier circuit, ΔI flows through the resistor Rg and Ia,
When Ib changes, the transistors Q ₃ , Q ₄ and Q ₅ , Q
₆ Nobesu current Ic, by Id varies, the transistor Q _1, Q ₂ each transistor Q _1, the V _BE Q ₂ 'different results affecting the collector current of the potential difference between the input voltage (Va- An error occurs between Vb) and the voltage across the resistor Rg.

This is the gain coefficient K in the equation (1). An example of the gain coefficient K of the conventional operational amplifier circuit is shown by a broken line I in FIG. As shown in FIG. 4, the gain coefficient K is equal to the external resistance Rg.
For example, when Rg = 10 kΩ, K =
It is 0.92, but increases as the resistance value increases and approaches 1. On the other hand, since the gain of the operational amplifier circuit is obtained by multiplying the resistance ratio (Rs / Rg) by the gain coefficient K as given by the equation (1), the resistors Rs and Rg are used to obtain a predetermined gain.
It was difficult to set the resistance value of.

In view of the above, in the present invention, the resistors Rs and Rs
An object of the present invention is to provide an operational amplifier circuit which can easily obtain a predetermined gain by setting a resistance value of g.

[0010]

SUMMARY OF THE INVENTION The above-mentioned problem is solved by the configuration shown in FIG.

That is, a first transistor Q ₁ having a collector supplied with a current from the _first current source J ₁ and a first input voltage Va applied to a base, and a second current source J ₁ having a collector second transistors Q ₂ to which current from the ₂ second input voltage Vb is applied to the base over the scan is supplied, connected between the first and second transistors Q _1, Q ₂ each of the emitter first 1 resistor Rg and the first and second current sources J ₁ and J ₂
Current detecting means 11 for detecting a change in the current ΔI flowing through the first resistor Rg and outputting first and second detected currents i ₁ and i ₂ ; Current generating means 1 for generating a current I _OUT equal to the current ΔI flowing through the first resistor Rg according to the _second detected currents i ₁ and i ₂
2, an amplifier 13 and a second resistor Rs supplied with the output current I _OUT of the current generator 12 and connected in series, and the difference between the first input voltage Va and the second input voltage Vb. voltage, the operational amplifier circuit that amplifies and outputs in accordance with the first and the resistance ratio of the second resistor, a current detector 11, the
1 of the collector current of the transistor Q ₁ and the first resistance Rg
In response to the current flowing through the first resistor Rg
A first current detection circuit 14 for outputting a first detection current i ₁ has Flip, first detection current i ₁ of the first current detection circuit 14
There a first current compensation circuit 15 for compensating so as not to affect the first collector current of the transistor Q _1, a second Trang
A second current detection circuit 16 for outputting a second detection current i ₂ that corresponds to the current flowing in the first resistor Rg is connected to the other end of the register Q ₂ of the collector current of the first resistor Rg, The second current compensating circuit 17 compensates the second detected current i ₂ of the second current detecting circuit 16 so as not to affect the collector current of the second transistor Q ₂ .

[0012]

According to the present invention having the above structure, the voltage across the first resistor Rg is higher than the input voltages Va and Vb of the first and second transistors by the base of the first and second transistors. The voltage becomes lower by the emitter-to-emitter voltage, and (Va−V
b).

If the input voltages are different, the current .DELTA.I flows through the first resistor Rg and the current generating means 12 generates the output current _I.sub.OUT (= .DELTA.I), but the current .DELTA.I flowing through the first resistor Rg. There first detection current i ₁ and the second detection current i ₂ are each first and second transistors to Q ₁ second current detection circuit 16 of the first current detection circuit 14 also varies, Q ₂
Since the voltage between the base and the emitter of the first and second transistors Q ₁ and Q ₂ is maintained unchanged without any change, the voltage across the first resistor Rg is ( Va−Vb).

[0014]

FIG. 2 is a circuit diagram of an embodiment of the present invention. 5, the same components as those of FIG. 5 are denoted by the same reference numerals, and the description thereof will be appropriately omitted.

The current detecting means 2. 11, the transistor Q _3, a first current detection circuit comprising a Q ₄ 14 and transistor _{Q 9, Q 11, Q 13} , Q 15 first current compensation circuit 15 consisting of, Further, a second current detection circuit 16 composed of transistors Q ₅ and Q ₆ symmetrically configured with the above circuit
And a first current compensation circuit 17 including transistors Q ₁₀ , Q ₁₂ , Q ₁₄ , and Q ₁₆ .

[0016] The first and second current detection circuits 14 and 16 operates similarly to the conventional circuit described above, the collector current (1/2) of the transistor Q ₃ in response to a change in current ΔI flowing through the resistor Rg Ia and the collector current of the transistor Q ₆ (1
/ 2) Ib increases and decreases. And, as mentioned above,
An output current I _OUT equal in magnitude to ΔI flows through the resistor Rs in a direction according to the magnitude relationship between the first and second input voltages Va and Vb, and a predetermined output voltage V _OUT is obtained at the output terminal 7.

The first current compensating circuit 15, which is a main part of the present invention, operates as follows.

Transistor Q ₉ and transistor Q ₁₁
Is the same characteristics as the respective transistors Q _4, and the current density of the transistor Q ₁₅ is three times the current density of the transistor Q _13.

[0019] Therefore, a current flows to the collector of the transistor Q ₉ Ia is equal to the current flowing in the collector of transistor Q ₄ Ia. Therefore, the collector current Ia of the transistor Q ₄ is, for example ΔIa in response to changes in ΔI
The base current Ic of the transistors Q ₃ and Q ₄ increases by Δ
When Ic increases, the transistor Q ₉ Nobesu current is also ΔI
As a result, the collector current I of the transistor Q ₉ increases.
a also increases by ΔIa.

[0020] Then, the change in the reference current to become the transistor Q ₁₁ Nobesu current of the current mirror pair transistors Q _13, Q ₁₅ increasing by DerutaIc, each increasing the collector current of the transistor Q ₁₅ is only 3ΔIc Since the current flows in the opposite direction to the base current Ic, the transistors Q ₃ , Q ₄ , Q
_Nine changes in the base current Ic are canceled out.

[0021] Consequently, since the current flowing in the collector of the transistor Q ₁ is always constant, the transistor Q ₁ Nobesu-emitter voltage does not change when the voltage across the resistor Rg is changed.

[0022] Note that the transistor Q ₁₀ and the transistor Q ₁₂ is a respective transistor Q ₅ and the same characteristics, and the current density of the transistor Q ₁₆ is three times the current density of the transistor Q _14, a second current compensation never circuit 17 also of varying the transistor Q ₂ Nobesu-emitter voltage operates in the same manner.

Therefore, the change of the input voltage (Va-V
With respect to b), the voltage across the resistor Rg is constant. That is, the gain coefficient K in the equation (1) can be made substantially 1 as shown by the solid line II in FIG. For example, Rg = 1
At 0 kΩ, K can be set to 0.99 or more, and the gain of the operational amplifier circuit 20 can be obtained with an error of 1% or less by G ≒ Rs / Rg (2).

According to the present embodiment, since the gain of the operational amplifier circuit can be obtained with an error of 1% or less only by the resistance ratio of the resistors Rs and Rg, which are external resistors, the semiconductor operational amplifier circuit can be externally connected. There is an excellent feature that a predetermined gain can be easily set by selecting a resistance value.

Next, FIG. 3 is a diagram showing a modification of the above embodiment, and is an example in which a predetermined gain can be obtained with higher accuracy only by setting the resistance ratio.

FIG. 3 shows a configuration in which the first and second current compensation circuits 16 and 17 in FIG. 2 are replaced with first and second current compensation circuits 18 and 19, respectively. That is, the first
Current compensation circuit 18 connects the buffer transistor Q ₁₇ between the collector and base chromatography scan of the transistor Q _13, further between the collectors of the transistors Q _3, Q _4, each base over scan the transistor Q ₁₅ of Q ₉ It was connected to the transistor Q _19. As a result, the gain coefficient K of the operational amplifier circuit 21 approaches 1 more than the solid line II shown in FIG.

As described above, according to the above embodiment,
The gain can be set with high accuracy only by the resistance ratio, and it is easy to design a circuit when a semiconductor is used.

[0028]

According to the present invention as described above, the voltage across the first resistor is equal to the first voltage of the first and second transistors.
And the second input voltage is lower by the base-emitter voltage of the first and second transistors.
And the second detection current do not affect the collector currents of the first and second transistors, respectively.
And the base-emitter voltage of the second transistor does not change and is maintained equal, so that even if the current flowing through the first resistor changes, the voltage across the first resistor is changed to the first and second inputs. There is a feature that the voltage becomes the voltage of the voltage difference and the gain of the operational amplifier circuit is set only by the resistance ratio of the first and second resistors.

[Brief description of the drawings]

FIG. 1 is a block diagram of the principle of the present invention.

FIG. 2 is a circuit diagram of one embodiment of the present invention.

FIG. 3 is a circuit diagram of a modification of the present invention.

FIG. 4 is a diagram illustrating gain coefficients of an embodiment of the present invention and a conventional operational amplifier circuit.

FIG. 5 is a circuit diagram of an example of a conventional operational amplifier circuit.

[Explanation of symbols]

Reference Signs List 8 inverting amplifier (amplifying means) 10, 20, 21 operational amplifier circuit 11 current detecting means 12 current generating means 13 amplifying means 14 first current detecting circuit 15, 18 first current compensating circuit 16 second current detecting circuit 17 , 19 Second current compensation circuit J ₁ First current source J ₂ Second current source I ₁ Current source (first current source, second current source) I ₂ current source Q ₁ First transistor Q ₂ 2nd transistor Va 1st input voltage Vb 2nd input voltage Rg 1st resistance Rs 2nd resistance

Claims (1)

(57) [Scope of request for utility model registration] A current is supplied from a first current source to a collector, a first transistor having a first input voltage applied to a base, and a current supplied from a second current source to a collector. A second transistor having a second input voltage applied to the base, a first resistor connected between the emitters of the first and second transistors, and the first and second transistors Current detection means connected to a current source for detecting a change in current flowing through the first resistor and outputting first and second detection currents; first and second detection currents of the current detection means A current generating means for generating a current equal to the current flowing through the first resistor in accordance with the following: a second resistor and an amplifying means connected in series to which an output current of the current generating means is supplied; 1 and the second input voltage, the difference between the first and In an operational amplifier circuit for amplifying and outputting according to a resistance ratio of a second resistor, the current detection means includes a collector of one end of the first resistor and the first transistor.
Connected to a collector of the first transistor.
The first and second currents depending on a current and a current flowing through the first resistor .
A first current detection circuit for outputting a detection current of the first transistor, and a collector connected to the collector of the first transistor;
The first current detected by the first current detection circuit is added to the first detection current.
So that the collector current of the transistor is not affected
A first current compensating circuit for compensating a collector current of the first transistor; and a collector of the other end of the first resistor and the second transistor.
Connected to the collector of the second transistor
The second current in response to the current and the current flowing through the first resistor .
A second current detection circuit that outputs a detection current of the second transistor and a collector of the second transistor;
2 to the second detection current of the second current detection circuit.
So that the collector current of the transistor is not affected.
An operational amplifier circuit comprising a second current compensating circuit for compensating the collector current of the two transistors .