JPH0145671B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an analog arithmetic unit using a composite photocoupler and an inverting amplifier.

Conventional multipliers or dividers as analog arithmetic units perform addition or subtraction after logarithmically converting the multiplier, multiplicand, divisor, and dividend, respectively, and perform antilogarithmic conversion of the result to perform multiplication or division. .

Therefore, each analog multiplier or divider basically needs to have four functions: at least two logarithmic converters, one adder or subtracter, and one antilogarithmic converter, and even this alone is sufficient to configure the analog multiplier or divider. becomes complicated.

Additionally, both logarithmic converters and anti-logarithmic converters are prone to drift due to temperature changes, and in order to perform high-precision calculations, a temperature compensation circuit is required, resulting in extremely complex configurations. be.

Therefore, it is clear that an analog multiplier/divider that can also perform multiplication and division would have a more complex structure.

This invention was made to solve the above problems, and it is possible to directly perform multiplication or division operations using multiple input voltages, and it is also possible to perform multiplication or division operations directly using a plurality of input voltages. The purpose is to compensate for this and perform highly accurate calculations.

In order to achieve the above object, the present invention includes, in one container, one light emitting element and first and second light receiving elements having substantially the same amplification factor and temperature drift, which are formed close to each other on the same pellet. , a composite photocoupler in which the first and second light-receiving elements are arranged opposite each other so that they receive the light emitted from the light-emitting element substantially equally, and the light-emitting element is connected as a load, and input to the inverting input terminal. An operational amplifier that causes the light emitting element to emit light according to a voltage is provided, a constant current source and the first light receiving element are connected in series between the power supply and the ground, and the connection point thereof is connected to the non-inverting input terminal of the operational amplifier. and an inverting amplifier consisting of another operational amplifier, an input resistor connected to its inverting input terminal, and a feedback resistor connected between its inverting input terminal and output terminal. The second light-receiving element of the composite photocoupler is used as at least one of the resistor and the feedback resistor, and the input voltage of the inverting amplifier and the input voltage of the negative feedback amplifier controlling the composite photocoupler are calculated based on the result of calculation. The present invention provides an analog arithmetic unit characterized in that a corresponding output voltage is obtained from an output terminal of the inverting amplifier.

Embodiments of the present invention will be described below with reference to the accompanying drawings, with each operational amplifier used in the embodiments being considered as an ideal operational amplifier, ignoring its offset voltage and input leakage current.

FIG. 1 is a circuit diagram of a composite photocoupler used in the present invention and an amplifier that controls it.

In the figure, an input voltage Ein between input terminals a and b is applied to an inverting input terminal of an operational amplifier 1.

The composite photocoupler 2 includes a light emitting diode LED as a light emitting element in one container, and bipolar type phototransistors PT ₁ as first and second light receiving elements formed close to each other on the same pellet.
PT ₂ and the first and second phototransistors.
PT ₁ and PT ₂ are formed opposite to each other so as to receive the light emitted from the light emitting diode LED substantially equally.

The anode of the light emitting diode LED of this composite photocoupler 2 is connected to the output terminal of the operational amplifier 1 via a resistor _R1 , and its cathode is grounded. In addition, the collector of the first phototransistor PT ₁ is connected to the positive power supply +V via the constant current source 3, and is also connected to the non-inverting input terminal of the operational amplifier 1 to apply negative feedback, and its emitter is grounded. .

In this way, the light emitting diode LED of the composite photocoupler 2 is adjusted according to the input voltage Ein as a whole.
A negative feedback amplifier is configured in which the output of the first phototransistor _PT1 is negatively fed back while emitting light.

Next, the operation of the amplifier thus configured will be explained.

First, when the input voltage Ein applied to the inverting input terminal of the operational amplifier 1 increases, its output voltage decreases and the light emitting diode of the composite photocoupler 2 increases.
Since the current flowing through the LED is reduced, the amount of light emitted by the light emitting diode LED is reduced. By that,
The internal impedance (emitter-collector resistance) Z ₁ of the first phototransistor PT ₁ increases, and the voltage Ve at the point increases.

Conversely, when the input voltage Ein decreases, the output voltage of operational amplifier 1 increases and the light emitting diode
By increasing the current flowing through the LED, the amount of light emitted by the light emitting diode LED increases. By that,
The internal impedance Z ₁ of the first phototransistor PT ₁ becomes small, and the voltage Ve at the point becomes low.

In either case, the operational amplifier 1 controls the current flowing from its output terminal to the light emitting diode LED so that the voltage Ve at the point where the non-inverting input voltage becomes equal to the inverting input voltage Ein (Ve = Ein). Maintain equilibrium.

Therefore, there is a relationship between the input voltage Ein, the internal impedance Z ₁ of the first phototransistor PT ₁ , and the current Ic flowing from the constant current source 3 to the first phototransistor PT ₁ as shown in the following equation. To establish.

Z ₁ =Ve/Ic=Ein/Ic (1) In this equation (1), the current Ic is constant because the constant current source 3 is used. Therefore, the internal impedance Z ₁ of the first phototransistor PT ₁ of the composite photocoupler 2 changes in proportion to the input voltage Ein.

By the way, the first and second phototransistors
Since PT ₁ and PT ₂ are formed close to each other on the same pellet, they are affected by temperature changes in substantially the same way. In addition, the first and second phototransistors PT ₁ and PT ₂
are placed opposite each other so as to receive light from the light emitting diodes LED approximately equally.

Therefore, the first and second phototransistors
If PT ₁ and PT ₂ are formed so that their direct current amplification factors h _FE and temperature drifts are approximately equal, the first,
The same amount of photocurrent flows through the second phototransistors PT ₁ and PT ₂ .

That is, the internal impedance Z ₁ of the first phototransistor PT ₁ and the second phototransistor PT 1
The relationship shown in the following equation holds true with the internal impedance Z ₂ of PT ₂ .

Z ₂ = Z ₁ = Ein/Ic (2) Therefore, the internal impedance of the second phototransistor PT ₂ of the composite photocoupler 2, that is, the output impedance between the output terminals c and d Z ₂
changes in proportion to the input voltage Ein, the same as the internal impedance _Z1 of the first phototransistor _PT1 .

Next, in this circuit, the second phototransistor of the composite photocoupler 2 is connected to the input voltage Ein.
We will discuss the effect of changes in ambient temperature when the internal impedance Z ₂ of PT ₂ is determined.

For example, when the temperature rises, the first and second phototransistors PT ₁ and PT ₂ each increase their DC current amplification factor.
Since h _FE increases, each photocurrent increases by about +1.0%/°C, although it depends on the magnitude of the DC current amplification factor h _FE .

Therefore, at this time, the output impedance between the terminals c and d by the second phototransistor PT ₂ tends to become small.

However, as the photocurrent of the first phototransistor PT ₁ increases, its internal impedance decreases, so the amount of negative feedback to the operational amplifier 1 increases, and the output voltage of the operational amplifier 1 decreases. As a result, the amount of light emitted from the light emitting diode LED decreases, so that the first and second phototransistors PT ₁ and PT ₂
The increase in photocurrent caused by temperature changes is suppressed.

Conversely, when the temperature decreases and the DC current amplification factor h _FE of the first and second phototransistors PT ₁ and PT ₂ decreases, the amount of negative feedback from the phototransistor PT ₁ to the operational amplifier 1 decreases, and its output decreases. Since the voltage increases and the amount of light emitted from the light emitting diode LED increases, a decrease in the photocurrent of the phototransistors PT ₁ and PT ₂ is suppressed.

In this way, even if the direct current amplification factor h _FE of the second phototransistor PT ₂ changes with temperature, the output impedance Z ₂ with respect to the input voltage Ein does not substantially change.

Fig. 2 shows a structure similar to Fig. 1 in which the phototransistors PT ₁ and PT ₂ , which are the first and second light-receiving elements of the composite photocoupler 2, are constructed by field-effect phototransistors instead of bipolar phototransistors. FIG. 2 is a circuit diagram of an amplifier.

The difference between this circuit and the circuit shown in FIG. 1 is that in its configuration, the drain of the first phototransistor PT ₁ is connected to the positive power supply +V via the non-inverting input terminal of the operational amplifier 1 and the constant current source 3, respectively. that its source is grounded and that its drain
The source-to-source resistance is the output impedance _Z2 , and its operation is similar to that of the amplifier shown in FIG. 1, so its explanation will be omitted.

FIG. 3 is a circuit diagram showing the basic principle of the inverting amplifier used in this invention.

This inverting amplifier has an inverting input terminal of an operational amplifier 4 connected to an input terminal f through an input resistor _R2 , an output terminal thereof through a feedback resistor _R3 , and a non-inverting input terminal connected to an input terminal f through a resistor _R4 . and grounded.

The relationship between the input voltage Ein inputted between the input terminals f and g of this inverting amplifier and the output voltage Eo outputted between the output terminals h and i will be explained.

If the operational amplifier 4 is considered as an ideal operational amplifier as described above, the currents I ₂ and I ₃ flowing through the input resistor R ₂ and the feedback resistor R ₃ are equal when the input voltage Ein is applied (I ₂ =I ₃ ).

As is well known, the following equation holds between the input voltage Ein and the output voltage _E0 at this time.

E ₀ =−R ₃ /R ₂ ·Ein (3) The minus sign in this equation (3) means phase inversion.

FIG. 4 is a circuit diagram showing an embodiment of the present invention, in which a first amplifier A ₁ and a second amplifier A ₂ each configured similarly to the negative feedback amplifier of FIG.
With the operational amplifier 4 as the third amplifier,
Multiplication and division can be performed at the same time using an analog arithmetic unit configured as an inverting amplifier as shown in FIG. 3 as a whole.

That is, the drain of the second phototransistor PT ₂ of the composite photocoupler 2 of the first amplifier A ₁ is connected to the input terminal f, and its source is connected to the inverting input terminal of the operational amplifier 4, respectively. In other words, the first
The second phototransistor PT ₂ of the amplifier A ₁ is used as the input resistor of the inverting amplifier (corresponding to the input resistor R ₂ in the inverting amplifier of FIG. 3).

Further, the drain of the second phototransistor PT ₂ ' of the composite photocoupler 2' of the second amplifier A ₂ is connected to the inverting input terminal of the operational amplifier 4, and the source thereof is connected to the output terminal of the operational amplifier 4, respectively.
That is, the second phototransistor PT 2 _' of the second amplifier A ₂ is used as a feedback resistor of the inverting amplifier (corresponding to the feedback resistor R ₃ in the inverting amplifier of FIG. 3).

The operation of the analog arithmetic unit configured in this way will be explained.

A first input voltage Ei _A is applied between the input terminals a and b of the first amplifier A ₁ , and the input terminals a′ and b of the second amplifier A ₂ are
When a second input voltage Ei _B is applied between b' and a third input voltage Ei _C is applied between the input terminals f and g of the inverting amplifier, the output obtained from the output terminals h and i of the inverting amplifier is applied. The voltage E ₀ is determined by the following equation corresponding to the above-mentioned equation (3).

E ₀ = −R ₃ /R ₂ · Ein = −Z ₂ ′ / Z ₂ · Eic ... (4) Here, the second phototransistor PT ₂ of the first and second amplifiers A ₁ and A ₂ , The internal impedances Z ₂ and Z ₂ ′ of PT ₂ ′ are expressed by the following equation corresponding to the above-mentioned equation (2).

Z ₂ = Ei _A /Ic ……(5) Z ₂ ′=Ei _B ／Ic′ ……(6) Substituting equations (5) and (6) into equation (4) above, the following equation is obtained. .

E ₀ = −Ei _B ／Ic´／Ei _A ／Ic・Ei _C ＝−Ic／Ic′・Ei ^B Ei
_C /Ei _A ...(7) Here, if -Ic/Ic' = K (constant), the output voltage E ₀ and the first, second, and third input voltages Ei _A , Ei _B , Ei _C
The relationship shown in the following equation holds true between .

E ₀ = K・Ei _B・Ei _C /Ei _A ...(8) In this way, as the output voltage E ₀ of the inverting amplifier,
Since the result of dividing the product of the third input voltage Ei _C and the second input voltage Ei _B by the first input voltage Ei _A is obtained, multiplication and division can be performed.

However, due to the characteristics of the circuit, the first and second input voltages
Ei _A and Ei _B can be used in the range of Ei _A ≧0 and Ei _B ≧0, respectively, and the third input voltage Ei _C can be used in the positive and negative ranges.

Also, the feedback resistance in the inverting amplifier shown in Figure 3
If only R ₃ is replaced with the second light receiving element T ₂ ' of the composite photocoupler 2', the output voltage E ₀ can be calculated using equations (4) and (6).
From the equation, it is determined by the following equation.

E ₀ = −Z ₂ ′/R ₂・Ei _C = −1/Ic′・R ₂・Ei _B・Ei _C …
…(9) Here, since 1/Ic′・R ₂ is constant, the output voltage E ₀ corresponding to the product of the input voltage Ei _B of the inverting amplifier and the input voltage Ei _C of the second amplifier A ₂ is It can be used as an analog multiplier.

Alternatively, if only the input resistor R ₂ in the inverting amplifier shown in FIG. 3 is replaced with the second photodetector PT ₂ of the composite photocoupler 2, the output voltage E ₀ becomes (4)
From equation and equation (5), it is determined by the following equation.

E ₀ = −R ₃ /Z ₂・Ei _C = −Ic・R ₃・Ei _C /Ei _A ……(10) Here, since Ic・R ₃ is constant, the input voltage Ei _C of the inverting amplifier is An output voltage E ₀ corresponding to the quotient divided by the input voltage of the first amplifier A ₁ is obtained, and can be used as an analog divider.

In the above description, an example is shown in which the amplifiers shown in FIG. 2 are used as the first and second amplifiers, but it goes without saying that the amplifiers shown in FIG. 1 may also be used.

In addition, although an example is shown in which a light emitting diode is used as a light emitting element of a composite photocoupler, a filament lamp etc. may also be used, and a light receiving element such as CdS or CdSe may be used instead of the first and second phototransistors. Good too.

As described above regarding the embodiments, the analog computing unit according to the present invention has a multiplier, a multiplicand, a divisor,
Direct multiplication or division operations can be performed using the input voltage representing the dividend, and the effects of temperature can be compensated for without the need for a special temperature compensation circuit, making the configuration extremely simple and highly accurate. calculations can be performed.

[Brief explanation of drawings]

FIGS. 1 and 2 are circuit diagrams showing different examples of a composite photocoupler and an amplifier for controlling it used in the present invention, and FIG. 3 is a circuit diagram showing the basic principle of an inverting amplifier used in the present invention. FIG. 4 is a circuit diagram showing an embodiment of the present invention. 1, 1'... operational amplifier, 2, 2'... composite photocoupler, 3, 3'... constant current source, 4... operational amplifier (for inverting amplifier), PT ₁ , PT ₁ '... first photo transistor , PT ₂ , PT ₂ '... second phototransistor, A ₁ ... first amplifier, A ₂ ...
Second amplifier.

Claims (1)

[Scope of Claims] 1. In one container, one light emitting element and first and second light receiving elements formed close to each other on the same pellet and having substantially the same amplification factor and temperature drift are placed. , a composite photocoupler 2, 2' arranged oppositely so that the second light-receiving element receives the light emitted from the light-emitting element substantially equally, and the light-emitting element LED,
Operational amplifiers 1 and 1' are connected to the LED' as a load and cause the light emitting element to emit light according to the input voltage to the inverting input terminal, and constant current sources 3 and 3' and the first The light receiving elements PT ₁ and PT ₁ ' are connected in series, and the connection point is connected to the operational amplifier 1,
1' non-inverting input terminal and connect it to the negative feedback amplifier.
A ₁ , A ₂ , and an inverting amplifier consisting of an operational amplifier 4, an input resistor connected to its inverting input terminal, and a feedback resistor connected between its inverting input terminal and output terminal.
The second light receiving elements PT ₂ and PT _{2 ' of the composite photocoupler 2 and 2} ' are used as at least one of the input resistor and the feedback resistor, and the input voltage Eic of the inverting amplifier and the composite photocoupler 2 are connected to each other. , 2' are controlled by negative feedback amplifiers A ₁ , A ₂
An analog computing device characterized in that an output voltage Eo corresponding to the result of computing input voltages Ei _A and Ei _B of the inverting amplifier is obtained from an output terminal of the inverting amplifier.