JPH03196280A - Multi-input operational amplifier circuit and integrating circuit using the amplifier circuit - Google Patents

Abstract

PURPOSE:To process the addition and the subtraction at one time by using a voltage/current converter containing an emitter negative feedback resistance and a differential amplifier set at the output stage of the voltage/current converter. CONSTITUTION:A voltage/current converter A which converts the input signal voltage into a logarithmic function is provided together with a differential amplifier B having high gains which secures the single output from the output of the converter A. Thus an operational amplifier circuit is obtained. A signal input stage converts the input signal voltage into a differential current via the emitter negative feedback resistances R1 and R2 and supplies the differential current to a diode D2. Then a transistor differential pair is biased with the forward voltage of the diode D2. Thus the single output is obtained. Thus an accurate operation is secured despite a high impedance of a signal source.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention is suitable for ultra-wideband semiconductor integrated circuits, and includes:
In particular, it relates to multi-input operational amplifier circuits suitable for adders, integrators, active filters, etc.

[Conventional Example] FIG. 7 is a circuit diagram showing a conventional example in which a conventional operational amplifier circuit is used as an adder circuit.

In the figure, input terminal 30. From 30s to 30s, the input signal voltage 1. to ■, N is applied, and operational amplifier A.

Inverting input terminal and input terminal 30. A plurality of weighting resistors Rffl to R3N are connected between the inverting input terminal and the output terminal 5, and a negative feedback resistor R4° is connected between the inverting input terminal and the output terminal 5. Current 1 flowing through resistors R31 to R3,4
1 to iN are expressed as follows.

l = i, +i2-t---+iN! ＋ −
Vll/R311L =L□/Rsz.

・-' N -V I N/ R11N Therefore, resistance L
The currents iI to i flowing through l to R3N are feedback resistors R
Flows at 4°. If the current is i, then the output voltage is ■. is expressed as the following equation.

■. −−R4゜i −−R1゜(i, +i2 + −・−−−+ i N
)-R4o (Vz/R:+++V+z/R:+z+-1VI,,/RxN) ・・−１−−−・−−−−−−(1) General operational amplifier circuit shown in Fig. 7 As is clear from the above equation, the adding circuit according to the above is configured to add arbitrary weights to a large number of input voltages using external resistors R31 to R3N, respectively. Usually, these resistors R3+ to R3N are constructed by mounting chip resistors or the like on a printed circuit board.

[Problem to be solved by the invention]

An adder circuit using a general operational amplifier circuit as shown in FIG. 7 has a drawback that the signal source impedance becomes extremely high because a relatively large resistance is added to the signal input stage. That is, there is a drawback that the operational amplifier circuit has extremely high input impedance. Also, when this operational amplifier circuit is used as an integrating circuit, a resistor is added to its inverting input terminal, which is a factor of the integral constant. When an operational amplifier circuit of this type is connected in multiple stages, such as in a ladder-type active filter, the influence of the signal source impedance may be affected because a resistor is connected to the input stage. Because of this disadvantage, it is necessary to use these resistors as small as possible, or they cannot be used in active filters or the like.

Moreover, since the resistors R31 to RffN are connected to the parasitic capacitance generated at the input stage of the operational amplifier circuit, there is a drawback that the frequency characteristics in the high frequency band are deteriorated.

Furthermore, the adder circuit shown in Fig. 7 is a phase inversion type adder circuit and shows an example in which negative signals are added, but when adding positive signals, this addition It is necessary to add an adder circuit for adding a positive signal to the output stage of the circuit, which has the drawback of making the circuit extremely complicated both in terms of structure and constant calculation.

In addition, as shown in FIG.
Since AIN is an external chip resistor, conventional operational amplifier circuits have the disadvantage of increasing the number of components.

The present invention has been made to improve the above-mentioned drawbacks, and its main purpose is to provide an adder that can perform accurate calculations even when the signal source impedance is high, and that has operational amplifier circuits connected in multiple stages. , an integrator, an active filter, and the like.

Another object of the present invention is to provide an operational amplifier circuit capable of processing addition and subtraction simultaneously.

(Means for Solving the Problems) A multi-input operational amplifier circuit according to the present invention is provided with a plurality of input terminals, a number of emitter negative feedback resistors corresponding to the input signals, and a number of emitter negative feedback resistors corresponding to the input signals. Consists of a voltage-current converter that converts the input signal voltage into a differential current having a logarithmic function via a negative feedback resistor, a differential pair of transistors that obtains the output of the voltage-current converter as a single output, and its active load circuit. It consists of a differential amplifier.

[Effect]

In the multi-input operational amplifier circuit of the present invention, the signal input stage converts the input signal voltage into a differential current through the emitter negative feedback resistor,
The differential current is caused to flow through the diode, and the forward voltage of the diode biases the differential pair of transistors to obtain a single output.

〔Example〕

FIG. 1 is an embodiment for explaining an operational amplifier circuit according to the present invention.

The operational amplifier circuit shown in FIG. 1 is composed of a voltage-current converter A that converts an input signal voltage into a logarithmic function, and a high-gain differential amplifier B that obtains a single output from the output to the voltage-current converter. 1 and 2 are inverting input terminals, 3.4 is a normal input terminal, 5 is an output terminal, and 6.7 is a power supply voltage terminal and a ground terminal, respectively.

First, the voltage-current converter A will be explained. Inverting input terminals 1 and 2 are transistors Q whose collectors are commonly connected;
, Q, and the emitters of these transistors Q, , Qt are connected to current source circuits 8 and 9, respectively. The normal input terminal 3.4 is connected to a transistor Q3.4 whose collectors are commonly connected. connected to the base of Q, respectively,
Those transistors Q3. Current source circuits 10 and 11 are connected to the emitters of Q and Q, respectively. The power supply voltage terminal 6 is connected to the cathode of the diode D.
The cathodes of diodes D2.0:l are connected to the anodes of diodes D2.0:l, and the cathodes of diodes Di, D3 are connected to the common connection point of the collectors of transistors Q, , Q, respectively, and transistors Q3. Q, is connected to the common connection point of the collectors of Q. An emitter negative feedback resistor R is connected between the emitters of transistors Q and Q3, and an emitter negative feedback resistor R2 is connected between the emitters of transistors Q2 and Q4.

The differential amplifier B, which is the output stage of the voltage-current converter A, includes a transistor Qs forming a differential pair of transistors.

A constant current source circuit 12 is connected between the commonly connected emitters of Q6 and the power supply voltage terminal 6, and an active load circuit consisting of transistors Q, , Q is connected to their collectors. The collectors of the transistors Q, ,Q, are commonly connected and connected to the output terminal 5. Transistor Q5 is
Its base is diode D2 and transistor Q, ,Q,
is connected to the connection point with the collector. Transistor Q6 has a diode D at its base and a transistor Q
It is connected to the connection point of the collector of 3°Q4 and is biased respectively. A load circuit R4 is connected between the output terminal 5 and the ground terminal 7.

In the embodiment shown in Figure 1, the voltage between input terminals 1 and 3 is
1, and the voltage between input terminals 2 and 4 is 2. The differential currents flowing through the emitter negative feedback resistors R, , R, are respectively I+,
If Iz, the differential current 1. ,I.

is expressed by the following relational expression.

1+ −V+ /R+ −−−・・−・−−−−−−
−−−−−(2) I z = V 2 / Rz −
−−−−−−−−−−−(3) Also, if the constant current flowing through the constant current source circuits 8 to 11 is I, then the transistor Q
The collector currents of Q1 to Q4 are (1,, -11), respectively.
(In-I2), (1,.

+ 1 +), (1, + It). Therefore,
These collector currents are added to the input terminals V, , V2
is diode D2. Logarithmically transformed by D3, the forward current IA, 1. Obtained by binding.

IA=21. , − (1, + Iz ) −−m−−
--(4)L =21fi+ (It +Iz)
−・−・−・・−(5) Also, diode D2. If the potential difference between the cathodes of D3 is ΔV, it is expressed as ΔV−Vt In (Is + IA).

On the other hand, the differential pair transistor Qs of the differential amplifier B.

The collector current of Q6 is the current flowing through the constant current source circuit 12. When the signal current is Δi, Nx-Δ
i), a current of (lx+Δi) will flow. The potential difference Δ■ between the collectors of the transistors Q, , Q, is expressed as follows.

Therefore, from equations (6) and (7), it is expressed as the following equation.

Here, when I and +12 are Ic, the equation (8) is expressed as the following equation.

21, −1c lx −Δ1 When the signal current Δi is determined from the formula (9), it is expressed as 00) and the formula (2)
Substituting the equation and equation (3), it is expressed as 1°.

Therefore, if the output current 2Δi flowing through the load circuit RL is Io, the output current I0 is determined by r, -2Δ
i X --- (V+ / R+ + Vz /
Rz ) −・−02) r, 1 .

02) Output current I from the formula. is the emitter negative feedback resistor R
It is clearly shown that a factor of 1,' Rz is included and that the input voltages are converted to currents and summed.

On the other hand, in the embodiment shown in FIG. 2, the voltage-current conversion circuit A is different from the embodiment shown in FIG. N are arranged, and input terminals 1° to is, 3. 3N are connected, transistors 11 to Q I N
A current source circuit is connected to the emitter of 8. 8N are connected to the emitters of the transistors Q z + to Q 2N, and a current source circuit 10. 10M are connected. Transistors 75 to Q1N and Q z + to Q zN arranged symmetrically form an emitter negative feedback resistor R1 between their respective emitters.
1 to RIM are connected. Incidentally, the differential amplifier RWB in the output stage has the same configuration as the embodiment shown in FIG.

In the embodiment of FIG. 2, the voltage-current converter A has input terminals 1. This is another embodiment of a multi-input operational amplifier circuit including a plurality of IN to IN and 31 to 3H. Input terminals 11 and 3. ~I
Assuming that the voltages between N and 3.4 are 1 and V9, respectively, the output current I of this embodiment is.

can be estimated from equation 02) and expressed as the following equation in the embodiment of FIG.

T.

Io −m−・(V l/nz +−−−−−+
VN/RIN)■,.

θω 03) As shown in the formula, the emitter negative feedback resistors R to R
The input voltages are weighted and added by IN.

In the embodiment shown in FIG. 3, the output voltage ■ is applied to one end of the inverting input terminal of the multi-input operational amplifier circuit shown in FIG. is a negative feedback circuit. The input voltage V, , is applied to the normal rotation input terminals 21 and 22.
V, is applied, and the input voltage ■3 is applied to the inverting input terminal 23.
is entered. Output voltage from output terminal 5■. is output, and at the same time the output voltage ■. is fed back to one end of the inverting input terminal. If the embodiment shown in FIG. 3 is described using a signal diagram, it can be expressed as shown in FIG. 4.

The embodiment shown in FIG. 3 will be described based on the signal diagram shown in FIG. 4. The embodiment shown in FIG. 1 is a current-operated type, but
Convert it to voltage and show the signal diagram in Figure 4, and its output voltage ■. is expressed as the following equation.

Vo −A −At(Vi ”−Vo)+A −AX
(V2-13) (However, A + and A 2 are a transistor pair provided in the input stage of the voltage-current conversion circuit A,
The amplification factor of the differential pair consisting of the emitter negative feedback resistor connected between the emitters of these transistors) Here, A2 /A, ``'k'' The two equations can be expressed as the following equation. be done.

vo=V, 4-kL -kVi (However, A, /A, =, 1/A-A, is approximately zero, and A.A,)1. ) Here, if k=1, the output voltage ■. ■.
−■ 1 −to Vz Vs −−−−
---It is expressed as 0ω.

Therefore, by connecting the multi-input operational amplifier circuit of the present invention as shown in the embodiment of FIG. 3, the multi-input operational amplifier circuit of the present invention can process addition and subtraction simultaneously.

In the embodiment shown in FIG. 5, the non-inverting input terminals of the multi-input operational amplifier are commonly connected, the input signal v3 is input to one end of the inverting input terminal, and the output voltage ■ is input to the other inverting input terminal. is connected so that it is returned. In this case, the output voltage ■. is expressed as the following equation.

■. = (1+k)V, -kV3 is set to -1, then V o = 2 V , -V , ----------
------041. In this example, the input signal voltage ■.

This shows that it is possible to double the voltage and input it to the voltage/current amplifier A.

The embodiment shown in FIG. 6 is the normal input terminal 2 of a multi-input operational amplifier.
1.22 is an application example in which input voltages V, , V2 are applied to each, and output voltage V0 is fed back to each inverting input terminal, and the output voltage of this embodiment is (2). is expressed as the following equation.

If k=1, It can be expressed as.

Furthermore, although not shown, by connecting a capacitor C between the output terminal 3 of the embodiment of FIG. 3 and ground, the multi-input operational amplifier circuit can be used as an integrating circuit. Output voltage■. is expressed as in equation 03). Therefore, Vo = V + 10Vz-V3 = Vi ---
--03)".

Since content C is connected to output terminal 5, the output voltage is ■. is expressed as the following equation.

(However, the mutual conductance g of a multi-input operational amplifier circuit
rn is expressed as gm=x7r. C is the capacitance of the capacitor. ) Therefore, from equations 03) and 06), the transfer function is:
V, V, →-V2 V:l
It is expressed as 5Cr00'.

Therefore, the internal resistance r of the multi-input operational amplifier circuit can be expressed as follows.

As is clear from equation q'7), the integral constant can be varied by changing the constant current lx, In of the multi-input operational amplifier circuit. Such an integrating circuit can be applied as an active filter, and the signal source impedance can be lowered than that of conventional integrating circuits, so even if this integrating circuit is connected in multiple stages, the high frequency characteristics will be , it can be made extremely good.

(Effects) As described above, the multi-input operational amplifier circuit of the present invention is formed of a voltage-current converter equipped with an emitter negative feedback resistor and a differential amplifier at its output stage, and according to this multi-input operational amplifier circuit, It is possible to form an addition/subtraction circuit that can process addition and subtraction simultaneously using an extremely simple circuit.Also, since no external resistor is required for weighting, the signal source impedance is extremely low. Therefore, adding circuits, integrating circuits, etc. can be easily formed using such multi-input arithmetic circuits, and these circuits can be connected in multiple stages to form active filters, etc. It is possible to form.

Furthermore, since the multi-input operational amplifier circuit of the present invention obtains a differential current using emitter negative feedback resistors, the number of external resistors can be reduced, and the number of components can be reduced. It is possible to reduce the parasitic capacitance that occurs between the two, and since external resistance can be reduced, it is possible to improve high frequency characteristics, making it extremely useful for high frequency active filters, etc. Effective.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a circuit diagram showing one embodiment of the multi-input operational amplifier circuit according to the present invention, and FIG. 2 is a circuit diagram showing another embodiment of the multi-input operational amplifier circuit according to the present invention. Circuit diagrams shown in Figures 3, 5, and 6
The figure is a circuit diagram for explaining an application example of a multi-input operational amplifier circuit, Figure 4 is a signal diagram of Figure 3, and Figure 7 is an example of an adder circuit using a conventional operational amplifier circuit. It is a circuit diagram. △: Voltage-current conversion circuit, B two differential amplifier, ■, 2: Inverting input terminal, 3, 4: Normal input terminal, 5: Output terminal, 6:
Power supply voltage terminal, 7: ground terminal, 8 to 12: constant current source circuit.

Claims (7)

[Claims] (1) A voltage-current converter comprising a plurality of input terminals to which a plurality of input signal voltages are respectively supplied, and converting the voltage into a logarithmic function current through a number of emitter negative feedback resistors corresponding to the input terminals; It is characterized by consisting of a differential pair of transistors biased by the output of the converter and an active load circuit of the differential pair of transistors, and a differential amplifier that outputs the output of the voltage-current converter as a single output from an output terminal. Multi-input operational amplifier circuit. (2) A negative feedback circuit is formed by connecting one of the inverting input terminals of the multi-input operational amplifier circuit to an output terminal of the multi-input operational amplifier circuit. Multi-input operational amplifier circuit. (3) Connect one of the inverting input terminals of the multi-input operational amplifier circuit to the output terminal of the multi-input operational amplifier circuit to form a negative feedback circuit, and connect the normal input terminal and the other inverting input terminal to the output terminal of the multi-input operational amplifier circuit. 2. The multi-input operational amplifier circuit according to claim 1, wherein the multi-input operational amplifier circuit is used as an input terminal for adding or subtracting input signal voltages. (4) One of the inverting input terminals of the multi-input operational amplifier circuit is connected to the output terminal of the multi-input operational amplifier circuit to form a negative feedback circuit, and at least two of the normal input terminals are connected in common. 2. The multi-input operational amplifier circuit according to claim 1, wherein the connection point and the other inverting input terminal are used as input terminals for adding and subtracting input signal voltages. (5) A voltage-current converter comprising a large number of input terminals that converts a plurality of input signal voltages into logarithmic function currents via an emitter negative feedback resistor, and a voltage-current converter that converts the output of the voltage-current converter into a single output. A multi-input operational amplifier circuit consisting of a differential amplifier consisting of a differential pair of transistors biased by the output of a current converter and an active load circuit for the differential pair of transistors, and a circuit between the output terminal of the differential amplifier and ground. An integrating circuit using a multi-input operational amplifier circuit, characterized in that it consists of a capacitor connected to a capacitor. (6) A differential amplifier consisting of a differential pair of transistors and an active load circuit, which has a voltage-current converter in its input stage that converts the input signal voltage into a logarithmic function current, and obtains a single output from the output of the voltage-current converter. an operational amplifier circuit configured such that the voltage-to-current converter has a cathode of a first diode connected to a second diode;
and the anode of the third diode are connected, respectively, and the second
The collectors of the first and second transistors are connected to the cathode of the third diode, respectively, the collectors of the third and fourth transistors are connected to the cathode of the third diode, and the collectors of the first to fourth transistors are connected to the cathode of the third diode. A current source circuit is connected to each emitter, a first emitter negative feedback resistor is connected between the emitters of the first and third transistors, and a second negative feedback resistor is connected between the emitters of the second and fourth transistors. An emitter negative feedback resistor is connected, the bases of the first and second transistors are used as first and second inverting input terminals, respectively, and the bases of the third and fourth transistors are used as the first and second inverting input terminals, respectively.
a normal input terminal of the transistor, and a connection point between the second diode and the first and second transistors is connected to the base of one transistor of the transistor differential pair; A multi-input operational amplifier circuit, characterized in that a connection point between the third and fourth transistors is connected to the base of the other transistor of the differential pair of transistors. (7) The input stage is equipped with a voltage-current converter that converts a plurality of input signal voltages into logarithmic function currents, and a differential transistor consisting of a differential pair of transistors and an active load circuit obtains a single output from the output of the voltage-current converter. The multi-input operational amplifier circuit according to claim 6, characterized in that the multi-input operational amplifier circuit is constituted by an amplifier, and an integrating circuit is formed by connecting a capacitor between the output terminal and the ground terminal of the differential amplifier. An integration circuit using an input operational amplifier circuit.