JPH0211942B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a voltage/impedance converter using a composite photocoupler and an analog divider using a constant current source circuit.

A conventional analog divider performs subtraction after logarithmically converting the divisor and dividend, and then performs division by inversely logarithmically converting the result.

Therefore, an analog divider basically needs to have four functions: at least two logarithmic converters, one subtracter, and one antilogarithmic converter.
This alone led to the problem of complicating the configuration.

Furthermore, both logarithmic converters and antilogarithmic 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. Ta.

The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide an analog divider that has a simple configuration, compensates for the effects of temperature, and can perform highly accurate division.

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. to configure a negative feedback amplifier, and connect the second light-receiving element, variable impedance element, and load resistor in series between a power supply and ground to determine the value of the current flowing through the second light-receiving element and the load resistor. A resistor is used, and the connection point between the variable impedance element and the second light receiving element is connected to the inverting input terminal of an operational amplifier to apply negative feedback, so that the voltage input to the inverting input terminal by the operational amplifier is a non-inverting input. A constant current source circuit that controls the variable impedance element so that the voltage is equal to the voltage input to the terminal, and a non-inverting input terminal of the operational amplifier of this constant current source circuit and an inverting input terminal of the operational amplifier of the negative feedback amplifier, respectively. and a division information input terminal for applying information to be divided and information to be divided, and an operation quotient information output terminal for taking out quotient information calculated from both ends of the load resistance of the constant current source circuit. It is.

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 voltage/impedance converter using a composite photocoupler used in the present invention.

In the figure, an input voltage Ein between input terminals a and b is directly 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 phototransistors _PT1 as first and second light-receiving elements formed close to each other on the same pellet.
and PT ₂ are formed opposite to each other so that the first and second phototransistors PT ₁ and PT ₂ receive substantially equal amounts of light emitted from the light emitting diode LED.

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 first phototransistor PT ₁
The collector of the amplifier is connected to the positive power supply +V via the constant current source 3, and also 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 voltage/impedance converter configured as described above 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 current flowing to the light emitting diode LED of the composite photocoupler 2 decreases, so the amount of light emitted by the light emitting diode LED increases. Decrease. 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.
The output voltage of 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 DC current amplification factor h _FE of the second phototransistor PT ₂ changes depending on the temperature,
The output impedance Z ₂ with respect to the input voltage Ein will not change substantially.

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 a voltage/impedance converter that constitutes a negative feedback 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. The source is grounded, and the drain-source resistance of the second phototransistor PT ₂ is set as the output impedance Z ₂ .The operation is the same as that of the circuit shown in Figure 1, so its explanation will be omitted. .

FIGS. 3 and 4 are circuit diagrams showing different examples of general constant current source circuits, respectively.

The constant current source circuit shown in FIG. 3 is a current inflow type constant current source circuit that sinks a constant current from a load resistor _R4 whose one end is connected to a positive constant voltage source +Vc.

The configuration of this constant current source circuit is such that the output terminal is connected to the input terminal f of the non-inverting input terminal of the operational amplifier 4 via a resistor _R2 , and then connected to a field effect transistor (FET).
Connect to the gate of _Q1 . Furthermore, the source of FET Q ₁ is grounded via a standard resistor R ₃ that determines the value of the constant current flowing through load resistor R ₄ , and is connected to the inverting input terminal of operational amplifier 4 to provide negative feedback.
A load resistor _R4 is inserted between the positive constant voltage source +Vc and the drain of FET _Q1 . In addition,
The presence or absence of resistor R ₂ does not directly affect operation.

To explain the operation of this constant current source circuit,
The operational amplifier 4 receives an input voltage Ein applied between input terminals f and g (non-inverting input terminal) and a voltage V _R input to its inverting input terminal (voltage drop across standard resistance R ₃ due to current I ₃ ). compared with
The output voltage applied to the gate of FET Q ₁ , which is a variable impedance element, is controlled so that both voltages are equal (V _R = Ein), thereby changing the impedance between the source and drain of FET Q ₁ .

Therefore, the relationship shown by the following equation is established between the input voltage Ein, the standard resistor R ₃ (its resistance value is R ₃ ), and the current I ₃ flowing through the standard resistor R ₃ .

I ₃ = Ein/R ₃ ......(3) Here, if the gate leakage current of FET Q ₁ is ignored (usually so small that it can be ignored), the current I ₄ flowing through the load resistance R ₄ is equal to the standard resistance R ₃ is equal to the current I ₃ flowing through (I ₄ =I ₃ ), so the current I ₄ is calculated from the above equation (3) as shown in the following equation.

I ₄ = I ₃ = Ein/R ₃ (4) In this way, the current I ₄ flowing through the load resistor R ₄ changes in proportion to the input voltage Ein.

Therefore, the input voltage Ein and the output terminal h−i
Output voltage obtained from between (both ends of load resistor R ₄ )
The relationship shown in the following equation holds true between E ₀ and E 0 based on equations (3) and (4) described above.

E ₀ = I ₄ · R ₄ = I ₃ · R ₄ = R ₄ /R ₃ · Ein (5) The constant current source circuit shown in Figure 4 applies a constant current to a load resistor R ₇ whose one end is grounded. This is a current drain type constant current source circuit.

The configuration of this constant current source circuit is such that the output terminal is connected to the input terminal k of the non-inverting input terminal of the operational amplifier 5 via a resistor R5, and then a field effect transistor (FET) is connected to the input terminal k of the non-inverting input terminal of the operational amplifier ₅ .
Connect to the gate of Q ₂ . In addition, the drain of FET Q ₂ is connected to the positive constant voltage source +Vc via a standard resistor R ₆ that determines the value of the constant current flowing through the load resistor R ₇ , and is also connected to the inverting input terminal of the operational amplifier 5 to connect the negative Apply for return. And ground and FET Q ₂
A load resistor _R7 is inserted between the source and the source.
Note that the presence or absence of resistor _R5 does not directly affect the operation.

To explain the operation of this constant current source circuit,
The operational amplifier 5 is designed so that the input voltage Ein applied between input terminals k and j and the voltage drop E _R across the standard resistance R ₆ due to the current I ₆ are equal (E _R = Ein), that is, the non-inverting input voltage Control the output voltage applied to the gate of FET Q ₂ so that it is equal to the inverted input voltage.

Therefore, the following relationship is established between the input voltage Ein and the standard resistor R ₆ (its resistance value is R ₆ ) and the current I ₆ flowing through the standard resistor R ₆ .

I ₆ = E _R / R ₆ = Ein / R ₆ (6) Here, if we ignore the gate leakage current of FET Q ₂ (usually so small that it can be ignored), the current I flowing through the load resistor R _{7 7} is equal to the current I ₆ flowing through the standard resistor R ₆ (I ₇ =I ₆ ), so the current I ₇ is calculated from the above equation (6) as shown in the following equation.

I ₇ = I ₆ = Ein/R ₆ (7) In this way, the current I ₇ flowing through the load resistor R ₇ changes in proportion to the input voltage Ein.

Therefore, the input voltage Ein and the output terminal l-m
Output voltage obtained between (across load resistor R ₇ )
The relationship shown in the following equation is established between E ₀ and E 0 based on equations (6) and (7) described above.

E ₀ =I ₇・R ₇ =I ₆・R ₇ =R ₇ /R ₆・Ein (8) FIG. 5 is a circuit diagram showing the first embodiment of the present invention, and is similar to FIG. 3. This is an analog divider constructed by a similar constant current source circuit _A1 and a voltage/impedance converter _A2 constituting a negative feedback amplifier similar to that shown in FIG.

That is, the second phototransistor of the composite photocoupler ₂ of the voltage-impedance converter A2
Connect the drain of PT ₂ to the source of FET Q ₁ of constant current source circuit A ₁ and the inverting input terminal of operational amplifier 4, and ground the source.

In other words, the output impedance of voltage-to-impedance converter A ₂ , that is, the composite photocoupler 2
The internal impedance Z ₂ of the second phototransistor PT ₂ is used as a resistor (corresponding to the standard resistor R ₃ in Fig. 3) that determines the current value flowing through the load resistor R ₄ of the current-inflow type constant current source circuit A ₁ . use.

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

The _first input voltage Ei A is applied between the input terminals f and g of the constant current source circuit A1, that is, the non-inverting input terminal of the operational amplifier 4, and the first input voltage Ei _A is applied between the input terminals a and b of the voltage/impedance converter _A2 , that is, the operational amplifier 1. When applying the second input voltage Ei _B of the inverting input terminal of
The output voltage E ₀ obtained between the output terminals h and i, that is, from both ends of the load resistor R ₄ is determined by the following equation since R ₃ =Z ₂ in the above-mentioned equation (5).

In this case, input terminals f and g are division information input terminals that apply information to be divided, input terminals a and b are division information input terminals that apply information to be divided, respectively, and output terminals h and i
is a calculated quotient information output terminal that takes out the calculated quotient information.

E ₀ = R ₄ /Z ₂・Ei _A (9) Here, the internal impedance Z ₂ of the second phototransistor PT ₂ of the composite photocoupler 2 is calculated by the following equation corresponding to the above equation (2). It is determined by

Z ₂ =Ei _B /Ic (10) By substituting this equation (10) into equation (9), the following equation is obtained.

E ₀ = R ₄ /Ei _B /Ic・Ei _A =Ic・R ₄・Ei _A /Ei _B (11) Here, since the values of Ic and R ₄ are constant,
If Ic・R ₄ = K, then the output voltage E ₀ and the first and second
The relationship expressed by the following equation holds true between the input voltages Ei _A and Ei _B of .

E ₀ = K.Ei _A /Ei _B ………(12) In this way, the voltage corresponding to the quotient of the first input voltage Ei _A divided by the second input voltage Ei _B is obtained as the output voltage E ₀ . Therefore, division can be performed.

However, due to the characteristics of the circuit, the first and second input voltages Ei _A ,
Ei _B can be used within the range of Ei _A ≧0 and Ei _B ≧0, respectively.

FIG. 6 is a circuit diagram showing a second embodiment of the present invention. In this embodiment, the constant current source circuit _A1 is constructed in the same manner as in FIG.
The output impedance of A ₂ , that is, the internal impedance Z ₂ of the second phototransistor PT ₂ of the composite photocoupler 2, is set to the current output type constant current source circuit.
It is used as a resistor (corresponding to the standard resistor _R6 in Figure 4) that determines the current value flowing through the load resistor _R7 of _A1 .

Therefore, the input terminal j− of constant current source circuit _A1
When the first input voltage Ei _A is applied between the terminals k and _{the second} input voltage Ei _B is applied between the input terminals a and b of the voltage/impedance converter A2, between the output terminals l and m,
In other words, the output voltage E ₀ obtained from both ends of the load resistor R ₇ becomes R ₆ = R ₇ in the above equation (8),
Further, since the internal impedance Z ₂ of the second phototransistor PT ₂ is as shown in the above-mentioned equation (10), it can be determined by the following equation.

E ₀ = R ₇ /Z ₂・Ei _A = R ₇ /Ei _B /Ic・
Ei _A = Ic・R ₇・Ei _A /Ei _B (13) Here, since the values of Ic and R ₇ are constant,
If Ic・R ₇ =K, then (12) of the first embodiment mentioned above.
It is similar to the expression, and division can be performed. However, the scope of its use is the same as in the first embodiment.
Ei _A ≧0 and Ei _B ≧0.

In this embodiment, input terminals j and k are division information input terminals that apply information to be divided, input terminals a and b are division information input terminals that apply information to be divided, respectively, and output terminals l and m take out calculated quotient information. This is an arithmetic quotient information output terminal.

In the above description, an example is shown in which the converter shown in FIG. 2 is used as the voltage/impedance converter, but it goes without saying that the converter shown in FIG. 1 may also be used.

Further, a filament lamp or the like may be used instead of a light emitting diode as the light emitting element of the composite photocoupler, and CdS, CdSe, etc. may be used instead of the phototransistor as the first and second light receiving elements.

As described above with respect to the embodiments, the analog divider according to the present invention can perform calculations directly using the input voltages representing the divisor and dividend, and is free from the effects of temperature without the need for a special temperature compensation circuit. Since the compensation is performed, the construction becomes extremely simple and high-precision division can be performed.

[Brief explanation of drawings]

FIGS. 1 and 2 are circuit diagrams showing different examples of voltage/impedance converters using composite photocouplers used in the present invention. FIGS. 3 and 4 are circuit diagrams showing different examples of general constant current source circuits, respectively. FIG. 5 is a circuit diagram showing a first embodiment of the invention. FIG. 6 is a circuit diagram showing a second embodiment of the invention. 1, 4, 5... operational amplifier, 2... composite photocoupler, 3... constant current source, PT ₁ ... first photo transistor, PT ₂ ... second photo transistor, R ₃ , R ₆ ... standard Resistance, R ₄ , R ₇ ...Load resistance, A ₁ ... Constant current source circuit, A ₂ ... Voltage/impedance converter.

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 in the same container. , a composite photocoupler 2 in which a second light-receiving element is arranged oppositely to receive the light emitted from the light-emitting element substantially equally, and the light-emitting element (LED) is connected as a load, and input to the inverting input terminal. An operational amplifier 1 is provided that causes the light emitting element to emit light according to a voltage, and a constant current source 3 and the first light receiving element PT ₁ are connected in series between the power supply and the ground, and the connection point is connected to the non-conducting point of the operational amplifier 1. It is connected to the inverting input terminal to form a negative feedback amplifier _A2 , and the second light receiving element _PT2 , the variable impedance element ( _Q1 or _Q2 ), and the load resistor ( _R4 or _R7 ) are connected to a power source. The second light receiving element PT ₂ is connected in series between the ground and serves as a resistor that determines the current value flowing through the load resistor, and the connection point between the variable impedance element and the second light receiving element is an operational amplifier (4 or 5). A constant is connected to the inverting input terminal of the operational amplifier to apply negative feedback, and controls the variable impedance element so that the voltage input to the inverting input terminal by the operational amplifier becomes equal to the voltage input to the non-inverting input terminal. Current source circuit _A1 and operational amplifier (4 or 5) for this constant current source circuit _A1
A division information input terminal that applies information to be divided and information to be divided to the non-inverting input terminal of the operational amplifier 1 of the negative feedback amplifier A ₂ and the inverting input terminal of the operational amplifier 1 of the negative feedback amplifier A ₂ , and a load resistance (R ₄ or _R7 )
1. An analog divider comprising: a calculated quotient information output terminal for extracting calculated quotient information from both ends of the divider.