JPH09260712A - Light receiving circuit and device using thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To compensate the effect of irregularity to the current transmissibility of a photocoupler. SOLUTION: Input voltage A is converted into a primary current by a voltage-current converter 1, and the light emitting element 2a of a photocoupler 2 is driven by the primary current. The light receiving element 2b of the photocoupler 2 receives the light generated by the light emitting element 2a and outputs a secondary current; the secondary current is proportional to the primary current and depends on the current transmissibility of the photocoupler 2. There is irregularity in every photocoupler in the current transmissibility, and accordingly, the secondary current possesses the magnitude depending on the current transmissibility of the photocoupler 2 to be used. From the voltage generated on the fixed resistor 3 by the above-mentioned secondary current, AC voltage X is extracted on one hand by a capacitor 4, and DC voltage E is extracted on the other hand by being fed to a DC detector 5. The AC voltage X is divided by the DC voltage E, by a dividing machine 6. The AC voltage of the output Z of the dividing machine 6 is not affected by the current transmissibility of the photocoupler 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting element that is current driven by a signal, and receives light from the light emitting element.
A photocoupler consisting of a light receiving element that generates a signal corresponding to the received light amount as an output current or a light receiving circuit attached to a light receiving element of an optical coupling communication system, a modem used for insulating the telephone line from the light receiving circuit, or exchange of optical signals The present invention relates to a device using the above-described light receiving circuit such as an optical communication device for performing communication by means of, and more particularly, to stabilization of a reception signal from a receiving element.

[0002]

2. Description of the Related Art A photocoupler is a safety component that constitutes a signal transmission system having an insulating function. A light emitting element that is current driven by a signal, and receives light from this light emitting element,
The light receiving element generates a signal corresponding to the amount of received light as an output current, and the signal input to the primary (light emitting) side is transmitted to the secondary (light receiving) side. Since the light emitting element and the light receiving element are separately formed and arranged at a distance, electrical insulation is ensured.

Similarly, an optical transmission path such as an optical fiber can be provided between the light emitting element and the light receiving element to perform short-distance or long-distance optical communication.

Since it is difficult to obtain stable amplitude characteristics in a photocoupler or an optical coupling communication system, only a frequency modulation signal (FM or FSK) or a phase modulation signal (PM or PSK) is transmitted and a limiter circuit is provided. We have tried to avoid the problem of amplitude characteristics by using a method to make the amplitude constant.

As a technique for obtaining a stable output amplitude using an optical coupling element, an example thereof is described in Japanese Patent Publication No. 60-57235. In this technique, two phototransistors and photodiodes are simultaneously provided as light receiving elements, and one of them is used as a compensating element to maintain a constant output of the system.

Techniques which require only one light receiving element and keep the amplification of the system constant are disclosed in, for example, Japanese Patent Laid-Open No. 64-82815, Japanese Patent Laid-Open No. 2-11014, and Japanese Patent Laid-Open No. 2-193.
No. 402, etc. These technologies are
It is characterized in that a signal on the light receiving side is logarithmically converted, then signal processed, and then inverse logarithmic conversion is performed.

A technique using an APD (avalanche photodiode) as a light receiving element and adjusting the bias voltage and varying the multiplication factor to perform gain control is disclosed in, for example, Japanese Patent Laid-Open No. 147533/56. Publication, JP-A-5
9-160345, JP-A-62-283710, JP-A-63-70625, JP-A-2-21.
1707, JP-A-3-27608, JP-A-3-80230, JP-A-3-188706, JP-A-3-213024, and JP-A-3-232.
No. 342, etc.

By the way, as an application of the photocoupler, there is a modem. To connect a modem to a telephone line, it is necessary to insulate the telephone line. To this end, the modem, as shown in FIG. 17, has a modulation / demodulation unit 121, a line interface unit 122 for connecting the modulation / demodulation unit 121 to a telephone line (not shown), and a modulation / demodulation unit 121 for a computer, a terminal, or the like. The line interface unit 12 is composed of a terminal interface unit 123 for connecting to a processing unit (not shown) and has an insulating function connected to a telephone line.
I have two.

In the line interface section 122, usually three kinds of insulating interface parts are used. It is also used as a line transformer for bidirectional transmission of data signals, a photocoupler for detecting call signals and supervisory signals sent from telephone lines, and a hooking switch for controlling hooking operations with electrical signals. It is a relay provided (electromagnetic relay or photo-MOS relay that is optically controlled).

The present applicant has previously proposed a card type modem using a photo coupler instead of the line transformer in the line interface section (Japanese Patent Application No. 6-103871).
issue). As shown in FIG. 18, the transmission side such as a modulator is connected between two opposing terminals A and C of the resistor bridge 102 via the photocoupler 100, and the reception side such as a demodulator is connected to the photocoupler 101. The resistor bridge 102 is connected between the other two terminals B and D facing each other. And
The telephone line 103 as a two-wire type is connected to the resistance bridge 10
It is connected between two adjacent two terminals C and D.

By setting the resistance bridge 102 in a balanced state, the transmission signal is sent to the telephone line 103 through the photocoupler 100 and the resistance bridge 102, is not sent to the receiving side, and is transmitted through the telephone line 103. The signal sent is a resistance bridge 102 and a photo coupler 101.
Is sent to the receiving side via.

In this structure, the function of insulating the telephone line from the
A line-to-four-line conversion function can be provided, bidirectional data transmission is possible, and since the photocouplers 100 and 101 are not bulky, they can be housed in a thinner card-shaped housing than before. . Further, it is excellent in safety, and when it is easy to mount and the cost of parts can be reduced, it is excellent in common-mode noise (noise generated in the same phase in two telephone lines).

In recent years, PCMCIA has been used as a card-type modem (MODEM) that is attached to a portable computer or an electronic notebook to enable communication via a telephone line.
(US standard) / JEIDA (domestic standard) TYPE2
Several standard sizes have been announced (length 85.6 mm, width 54 mm, thickness 5 mm). Using a photocoupler instead of a line transformer in this modem takes advantage of the above.

[0014]

Conventionally, in a photocoupler or an optical coupling communication system, regarding the transfer characteristics from the primary (light emitting) side to the secondary (light receiving) side, the light emitting efficiency of the light emitting element and the light receiving efficiency of the light receiving element. The current transmissibility as the product of and varies from element to element. FIG. 19 shows the state of this variation, and due to this variation, the transfer function has variation for each element. Therefore, when signal transmission is performed using a photocoupler or an optical coupling communication system, there is a problem in that the amplitude on the secondary (light receiving) side differs from element to element.

Further, in the optical coupling communication system, the length of the optical transmission line is remarkably different from several tens of meters to several tens of kilometers,
Due to this, the transmission loss is greatly different. Therefore, it is difficult to obtain stable amplitude characteristics even if there is no variation in the light receiving elements.

In recent years, for the purpose of transmitting a large amount of information using a photocoupler or an optical coupling communication system, a linear signal is directly transmitted or an amplitude modulation signal (AM or AS) is transmitted.
K) and quadrature amplitude modulation signals (QAM) are required to be transmitted.
In such a case, unstable amplitude characteristics are a major drawback such that the amplitude information included in the signal is changed and the signal transmission level of the system is different for each device.

To use two phototransistors and photodiodes at the same time as light receiving elements and use one of them as a compensating element, the phototransistors and photodiodes serving as light receiving elements are incorporated in the same photocoupler. It must be a special photo coupler. Therefore, it has a drawback that it cannot be applied to a photocoupler using one light receiving element which is usually commercially available.

If the above-mentioned technique is carried out in which the signal on the light receiving side is logarithmically converted, then signal processed, and then antilogarithmic conversion is performed, a large amount of power is consumed in the logarithmic-antilogarithmic processing. Comparing the secondary power consumption of an ordinary photocoupler to which this technology is not added with the secondary power consumption of a photocoupler to which this technology is implemented and a circuit for it is added, the latter is approximately 100 times This problem is a major drawback when applying such a photocoupler to a device.

Further, the technique of adjusting the bias voltage of the APD to vary its multiplication factor to perform gain control is premised on being applied to an element in which the multiplication factor changes sufficiently with respect to the magnitude of the bias voltage. However, even if it is applied to an ordinary photocoupler, there is no change in the multiplication factor with respect to the change in bias voltage, so there is no effect.

Particularly, in the conventional example similar to this technique, the signal amplitude is detected by a peak detection circuit or the like because the purpose is to make the signal amplitude constant. Therefore, the circuit is complicated and there is a problem in economical efficiency. It had the drawback of high power consumption.

In addition, since the APD itself is used by applying a bias voltage of 100 V or more, it is not appropriate to use it from the economical point of view except for a large-scale and expensive high-speed optical communication device.

Also, when a photocoupler is used instead of the line transformer of the modem, the variation of the transfer function
Fluctuation becomes a problem. The maximum transmission power is set based on the principle of ensuring publicity specified by the Telecommunications Business Law.
At the time of reception, even if the received power fluctuates, A in the modem
This can be removed by the action of the GC, but at the time of transmission, if there is a fluctuation / variation factor in the transfer function in the line interface part of the modem, the transmission power fluctuates, and the maximum transmission power above It may exceed.

As for the cause of this fluctuation / variation, when the photocoupler is used in the line interface section, the fluctuation / variation of the current transfer rate CTR of the photocoupler is the most serious problem. The transfer function in this case is the current transfer rate CTR.
Therefore, if the photocoupler fluctuates in the current transfer rate CTR due to manufacturing variations or temperature changes, the fluctuation range becomes the fluctuation range of the output power as it is.

Therefore, when the photocoupler is used in the line interface part of the modem, it is necessary to adjust the output power for each modem by the adjusting means. For example, it is conceivable to provide an adjusting means by a variable resistor so as to adjust the transmission output. However, according to this method, since there are variations in each photocoupler, it is necessary to adjust each modem, which is very troublesome.

Therefore, in order to compensate for such fluctuations in output power, it is conceivable to provide an AGC circuit to stabilize the amplitude. However, in this case, even if signals having different levels such as a data signal and a DTMF signal are used,
The inconvenience arises that the level becomes the same depending on the C circuit.

The object of the present invention is to solve the above problems,
It is an object of the present invention to provide a compensating circuit for a light-receiving element and a device using the compensating circuit that compensates for the influence of variations and fluctuations in the current transfer rate while eliminating the labor of adjustment.

[0027]

In order to achieve the above object, the first aspect of the present invention has a conversion gain control circuit for controlling the conversion gain of a light receiving element, and the circuit is a phototransistor. Photoreceptor operation that operates in the saturation region or that consists of a photodiode with a grounded-emitter transistor amplifier connected to the rear side and a photoreceptor that controls the operating point so that the photoreceptor operates in the unsaturated region of low voltage It is characterized by having a point control circuit.

In order to achieve the above object, a second aspect of the present invention is a modem for performing communication via a telephone line or an optical communication device for performing communication by exchanging optical signals.
It is characterized in that the light receiving circuit is provided.

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION Generally, when an APD is used in an optical coupling communication system, the current value flowing through a light receiving element increases as the bias voltage of the light receiving element increases. However, when a phototransistor, PIN diode, or PN junction diode that is commonly used as a light receiving element for a photocoupler is used, the power supply voltage dependency of the saturation region, which is the region in which the device operates, is usually small, Even if it is doubled, the current change is only a few percent. FIG. 20 shows this state. In the saturation region, the power supply voltage changes about 10 times, whereas the current change rate is only about 9%.

Therefore, if the photocoupler or the optical coupling communication system has a larger current transfer rate, the gain adjusting effect is hardly obtained only by providing the light receiving element power source voltage control circuit which operates so as to lower the power source voltage of the light receiving element.

The light receiving element is usually used in the saturation region because (1) the highest current transfer rate can be obtained in the saturation region.
(2) In the unsaturated region, the output current fluctuates greatly even if the operating point slightly fluctuates, so that the operation tends to become unstable. For this reason, the light receiving element is placed in an unsaturated region (see FIG.
1)) was not used in the prior art.

However, in this unsaturated region, FIG.
If the operating point is shifted by increasing or decreasing the collector voltage as shown in, the output current of the light receiving element can be changed independently of the input current of the light emitting element, and the instability of the operating point can be compensated by the control circuit.

Therefore, the operating point control circuit of the light receiving element shown in FIG. 1 is provided, the operating point of the light receiving element is located in the unsaturated region, and the operating point is moved to obtain the required conversion gain. The adjustment and stability of the operating point can be realized.

The light-receiving element operating point control circuit is provided with a photo-coupler or a light-receiving element of an optical coupling communication system, a resistor, an integrator, a transistor for generating a secondary power supply voltage, and a feedback loop including these components. The DC current value of the photocoupler or the light receiving element of the optical coupling communication system is operated so as to be set to a constant value in the unsaturated region by the reference voltage of the integrator and the value of the resistor (first means). .

As another means for reducing the power consumption, the compensating circuit for the light receiving element according to the present invention uses the AC extracting means for extracting the AC component of the output signal of the light receiving element and the DC component of the output signal of the light receiving element. A direct current extracting means for extracting and a dividing means for dividing the alternating current component by the direct current component are provided and included in the feedback loop.

As yet another means, an FET in which the output current of the light receiving element is supplied to the source to operate in the variable resistance region
A (field effect transistor) and an integrator which is supplied with a constant reference voltage and which integrates the difference between the DC voltage obtained between the source and drain of the FET and the reference voltage are provided. Then, the output of the integrator is supplied to the gate of the FET as a control voltage, servo is performed so that the DC voltage obtained between the source and drain of the FET becomes equal to the reference voltage, and the AC of the light receiving element is changed from the source of the FET. Try to get a voltage output.

Further, the modem according to the present invention is connected to the telephone line through a photocoupler having the compensation circuit for the light receiving element so as to insulate the telephone line.

In the first means, the output current of the light receiving element and the conversion efficiency are independently controlled by the circuit for controlling the conversion efficiency of the light receiving element, and the DC output current is kept constant.
The conversion efficiency is adjusted.

The function is not to make the absolute amplitude of the signal constant, but to make the transfer function from the primary (light emitting) side to the secondary (light receiving) side converge to a constant value.

The control circuit is added to the existing photo coupler to perform the control operation.

Also, the operating point of the photocoupler or the light receiving element of the optical coupling communication system changes due to the action of the light receiving element operating point control circuit, but the operating point is within the unsaturated region.

The light-receiving element operating point control circuit changes the operating point (= “voltage across both ends” / “flowing current” value) of the secondary-side light-receiving element to reduce fluctuations in the current transmissibility of the system. The control operation is performed to move the operating point.

With the above operation, the secondary side alternating current is proportional to the primary side alternating current and its proportional constant is constant, that is, from the primary side to the secondary side of the alternating current. The transfer function of becomes constant. Light receiving element,
A feedback loop containing a resistor, an integrator, and a transistor that generates a secondary power supply voltage detects the value of a direct current flowing through a photocoupler or a light receiving element of an optical coupling communication system, and the current value is an integrator. It acts so as to be fixed by the reference voltage and the value of the resistor. This action has a side effect that the transfer function of the alternating current from the primary side to the secondary side becomes constant.

In the method of dividing the AC voltage (current) of the output signal of the light receiving element by the DC voltage (current), even if the current transfer rate CTR of the photocoupler varies,
Since the AC current and the DC current of the output current of the light receiving element are almost the same for AC and DC, the AC current and the DC current of the driving current of the light emitting element are multiplied by almost the same CTR. Therefore, when the AC current of the output current of the light receiving element is divided by the DC current, the AC voltage after the output current of the light receiving element is calculated by the compensation circuit is determined independently of the CTR of the photocoupler. The effect is that it is not affected by variations and fluctuations.

Further, the output voltage of the light receiving element is supplied to the source to operate in the variable resistance region FET (field effect transistor), and a constant reference voltage is supplied to the DC voltage obtained between the source and drain of the FET. An integrator that integrates the difference from the reference voltage is provided, and the output of the integrator is supplied to the gate of the FET as a control voltage so that the DC voltage obtained between the source and drain of the FET becomes equal to the reference voltage. In the method of applying servo, the above FET
The output DC voltage obtained between the source and the drain of is according to the value obtained by multiplying the DC current of the drive current of the light emitting element by the CTR of the photocoupler.

When this is made equal to the reference voltage of the integrator by the servo, the output AC voltage obtained between the source and drain of the FET is always the output DC voltage obtained between the source and drain of the FET. If the AC / DC ratio of the current flowing through the photocoupler is constant, the output AC voltage is also not affected by variations and fluctuations in the CTR of the photocoupler, as long as the voltage is equal to the reference voltage.

Further, by using a photocoupler having such a compensation circuit in a modem as described above, variations in the transfer function of the photocoupler or the optical coupling section can be ignored, so adjustments for correcting variations in elements are made. Is unnecessary, and a stable maximum transmission power is set. Further, it is possible to compensate for the fluctuation of loss caused by the difference in the length of the optical transmission path and obtain a received signal with stable amplitude.

Specific examples of the present invention will be described below with reference to the drawings. 1 (a), (b) and (c) are circuit diagrams showing a first specific example of a light receiving element conversion gain circuit according to the present invention,
FIG. 1 (a) is a block diagram of an integrator, and FIG. 1 (b).
Is a diagram showing the integrator in a concrete circuit, and FIG. 1C is a diagram showing the integrator in another concrete circuit. In these figures, 201 is a voltage / current converter, 202 is a photocoupler, 202a is a light emitting element, 202b is a light receiving element, 203 is a fixed resistor, 204 is a transistor, 20
5 is an integrator, 206 is a constant voltage source, 207 is a power source, 208
Indicates an input terminal, and 209 indicates an output terminal.

In the light-receiving element operating point control circuit shown in FIG. 1, the operating point of the light-receiving element is located in the unsaturated region, and the operating point is moved to obtain the required conversion gain, and the conversion gain is adjusted. And stabilize the operating point. The operating points of the light receiving element are shown in FIG.

In FIG. 1, DC voltage VADC and AC voltage VA
The input voltage A composed of AC is converted into a current by the voltage / current converter 201, and the light emitting element 202 of the photocoupler 202.
Drive a. Accordingly, the light output from the light emitting element 202a is received by the light receiving element 202b, and
A current corresponding to the amount of received light is obtained from 2b.

This current flows through the fixed resistor 203, and a voltage B proportional to it is obtained. This voltage B is supplied to the integrator 205 and the DC voltage E is extracted. Integrator 2
When the voltage of the constant voltage source 206 is Vrefl, 05 supplies the base current of the transistor 204 so that the DC voltage E becomes equal to the voltage Vrefl. The power supply voltage supplied to the light receiving element 202b is equal to the potential difference (Vcc2-Ve) between this voltage Vcc2 and the emitter potential Ve of the transistor 204, where Vcc2 is the voltage of the power supply 207.

Here, the light emitting element 2 of the photocoupler 202
The direct current (primary direct current) flowing in 02a is I1, the alternating current (primary alternating current) is i1, and the photocoupler 20
The DC current (secondary DC current) flowing through the second light receiving element 202b is I2, the AC current (secondary AC current) is i2, and the DC and AC current transfer rates of the photocoupler 202 are CTRDC and CTRAC, respectively. The resistance value of the resistor 203 is R. Therefore, since the transfer function f (x) from the light emitting side to the light receiving side for an AC signal is generally approximately equal to the transfer function for a DC signal, f (x) = i2 / i1≈I2 / I1 = (E / R) / I1 = Vrefl / (R.I1). When the primary DC current I1 is supplied from a constant current source,
The transfer function for DC is uniquely and stably determined by Vrefl, R, and I1, and the transfer function for AC signals is almost equal to this. Therefore, the range of variation of the transfer function is
The current transfer rate CTR of the photocoupler becomes smaller than the range of variation, and the variation is compensated.

Next, another specific example will be described. In the first specific example, the value of the DC output current of the light receiving element itself is made constant by the action of the control circuit. On the other hand, in the following specific examples, the value of the output current of the light receiving element changes according to the variation / variation of the CTR of the photocoupler, but a constant voltage is calculated by calculating the current (or voltage) with the variation. Is to be converted to.

FIG. 2 is a block diagram showing a second specific example thereof. In the figure, 1 is a voltage / current converter, 2 is a photocoupler, 2a is a light emitting element, 2b is a light receiving element, 3 is a fixed resistor. , 4 is a capacitor, 5 is a DC detector, 6 is a divider, 7
Is an output terminal.

In the figure, an input voltage A composed of a DC voltage VADC and an AC voltage VAAC is converted into a current by a voltage / current converter 1 to drive a light emitting element 2a of a photocoupler 2. Thus, the light emitted from the light emitting element 2a is received by the light receiving element 2b, and the light receiving element 2b outputs a current according to the amount of light received. This current flows through the fixed resistor 3 and a voltage B proportional to it is obtained. This voltage B is supplied to the capacitor 4 on the one hand to extract the AC voltage X, and on the other hand to the DC detector 5 to extract the DC voltage E. The AC voltage X is supplied to the divider 6 and divided by the DC voltage E from the DC detector 5 to obtain the division force Z at the output terminal 7.

Here, the direct current (primary direct current) flowing through the light emitting element 2a of the photocoupler 2 is I1, the alternating current (primary alternating current) is i1, the direct current flowing through the light receiving element 2b of the photocoupler 2 (secondary current). The DC current) is I2, and the AC current (secondary AC current) is i2.
Let CTRDC and CTRAC be the current transfer rates of DC and AC, respectively. E = R · I2 = CTRDC · RI1 Then, the output Z of the divider 6 is

[0057]

[Equation 1]

When CTRDC = CTRAC,
Even if there are variations in the current transfer rate CTR between the photo couplers,

[0059]

[Equation 2]

Is as follows. Here, when the conversion coefficient of the voltage / current converter 1 is α, i1 = αVAAC and I1 = αVADC.

[0061]

(Equation 3)

As is clear from the equation 3, the output Z of the divider 6 is the current transmissibility C of the photocoupler 2 in this example.
DC voltage VAD of input A, which is not affected by TR
By stabilizing C, AC voltage VAAC of input A
A signal Z proportional to (that is, a signal component) is obtained, and by stabilizing the DC voltage VADC of the input A to, for example, 1 V, the signal voltage Z obtained at the output terminal 7 is equal to the AC voltage VAAC of the input A, In this specific example, the circuit has a gain of 1.

A conventional divider can be used as the divider 6, and an example thereof is a logarithmic conversion type.
This is because the multiplication input X and the division input Y are logarithmically converted by a logarithmic amplifier, and their outputs are subjected to the operation of Log (X / Y) = LogX−LogY by a subtractor, and the operation result Log (X / Y) Is subjected to antilogarithmic conversion by an antilogarithmic amplifier. Another example is Gilbert Cell.

However, in the divider by the logarithmic conversion method, the VBE-IC of the transistor is used for logarithmic conversion and inverse logarithmic conversion.
Since the characteristics are used, there is a problem that it is easily affected by temperature and that the Gilbert cell consumes a large amount of power. When the logarithmic conversion method is used by using the above divider in a modem, there is a temperature dependency, and therefore a Gilbert cell having an improved dependency must be used.

A direct current is superimposed on the telephone line, and it is set at a minimum of 20 mA in Japan, and the voltage across the line is 6 V or less when off-hook. Within this range, it is necessary to cover both the peak-to-peak value of the drive current of the signal sent to the line and the current for operating the circuit. Therefore, under such circumstances, the linear multiplier / divider used for the modem interface is
It is necessary to operate even under the condition of V, 1 to 2 mA. However, the Gilbert cell requires a power supply of about 10 V and 10 mA, and is not suitable for a modem interface.

FIG. 3 is a circuit diagram showing a specific example of a linear divider which can solve the above problems. Reference numerals 8 and 9 are input terminals, 10 is an FET, 11 is an integrator, 11a is an operational amplifier, and 11b is an amplifier. Is a capacitor, 11c and 12 are fixed resistors,
Reference numeral 13 is a capacitor, 14 is a DC voltage source, 15 is an inductor, and 16 is an output terminal.

In the figure, the input X from the input terminal 8 is supplied to the capacitor 13, the AC current XAC of the input X is extracted, and is supplied to the source S of the FET 10 via the fixed resistor 12. The drain D of the FET 10 is grounded. Further, the DC voltage E of the DC voltage source 14 is supplied to the source S of the FET 10 via the inductor 15 and the fixed resistor 12. The source S of the FET 10 is connected to the output terminal 16 and also to the integrator 11,
The output terminal of 1 is connected to the gate G of the FET 10.

In the integrator 11, the output terminal 16 (therefore,
DC voltage Z of output Z obtained at source S) of FET 10
DC is supplied as an inverting input to the operational amplifier 11a via the fixed resistor 11c, and a non-inverting input of the operational amplifier 11a is supplied with a DC voltage input Y as a reference voltage from the input terminal 9. These DC voltage ZDC and input Y
The output of the operational amplifier 11a, which is the integrated value of the difference between
It is supplied to the gate G of T10 as a gain control voltage. A capacitor 11b is provided between the input and output terminals of the operational amplifier 11a.

The FET 10 operates not in the active region but in the variable resistance region, and almost no voltage is applied between the drain and the source. The output of the integrator 11 is FET1
By applying the gain control voltage to the gate G of 0, the difference between the DC voltage ZDC of the output Z, which is the voltage between the source and drain of the FET 10, and the input Y, which is the reference voltage, becomes 0, that is, these DC Servo is applied so that the voltage ZDC and the input Y are equal.

Assuming that the resistance value between the source and drain of the FET 10 is r1 and the resistance value of the fixed resistor 12 is r0,

[0071]

(Equation 4)

[0072]

(Equation 5)

Is satisfied. Therefore, from equations 4 and 5,

[0074]

(Equation 6)

Regarding the AC voltage, if the impedance between the source and drain of the FET 10 is equal to r1,

[0076]

(Equation 7)

[Mathematical formula-see original document] When the above equation 6 is substituted into this, equation 8 is obtained.

[0078]

(Equation 8)

According to the equation (8), the AC voltage ZAC of the output Z obtained at the output terminal 16 can be obtained by setting the AC voltage XAC of the input X as the division input and the DC voltage E as the division input.
It becomes the divided input XAC divided by the division input E, and operates as a linear divider. However, the input Y is constant.

By the way, changes in resistance and impedance between the source and drain with respect to the control DC voltage applied to the gate of the FET are non-linear as shown in FIG. However, in this specific example, as described above, FET1
0 is a variable resistor, and the resistance and impedance between the source and drain of the FET 10 are controlled by the integrator 11 to perform servo control so that the DC voltage ZDC of the output Z becomes equal to the input Y, as shown in FIG. Such a non-linear characteristic is improved to function as a linear divider.

The power consumed in this example is shown in FIG.
It is considered that there are a direct current flowing through the resistance between the source and the drain of the FET 10 and a current consumed by the integrator 11. However, in the former case, the current flowing through the resistance between the source and the drain of the FET 10 is about 0.2 mA, and this resistance is sufficiently small. Therefore, the voltage generated in the resistance can be reduced to about 50 mV, so that the consumption of this resistance is reduced. The power can be about 0.01 mW. In the latter case, for example, if the operational amplifier 11a has a single power supply of 3 V and the power is 0.3 mA, the power consumption is 0.9 mW. Therefore, the total power consumption is very low.

Incidentally, for example, JP-A-64-82815, JP-A-2-11014, and JP-A-2-1933.
In a commercially available divider using a logarithmic method as described in Japanese Patent Publication No. 402, the power consumption is 128 mW, and this specific example is 1/100 or less of this divider.

Further, in this specific example, the output ZAC shown in the above equation 8 is obtained, so that the precision of multiplication and division is very high. An error factor that is considered to deteriorate the accuracy is the mismatch between the offset of the operational amplifier 11a and the DC resistance value between the source and drain of the FET 10 and the AC impedance in FIG. FIG. 4 is a characteristic diagram showing an example of changes in the resistance and impedance between the source and drain with respect to the control DC voltage applied to the gate of the FET. According to this characteristic, the control DC voltage is almost 2
It can be seen that when the voltage is higher than V, a mismatch occurs between these resistances and impedances. However, FETs in which they sufficiently match each other are commercially available, and using this solves this problem. Further, in this specific example, it has been experimentally confirmed that the deviation of the gain between DC and AC is within 5%, so that high accuracy can be obtained.

In FIG. 3, the inductor 15 is for preventing the AC voltage XAC from the capacitor 13 from leaking to the DC voltage source 5 side.

FIG. 5 is a circuit diagram used in an experiment for evaluating the linear divider shown in FIG.
Reference numerals 10b and 10c are FETs, and parts corresponding to those in FIG.

Here, as the FET 10, 3 2SJ105GR is used.
FE (FET 10a, 10b, 10c) provided in parallel,
The variable range of the resistance value of T is widened. The AD820 is used as the operational amplifier 11a, and the integrator 1
The cutoff frequency of 1 is 16 Hz, and the signal frequency is 3 kHz.
The inductance of z and the inductor 15 is about 1.2H. Moreover, 1 is provided between the two input terminals of the operational amplifier 11a.
A fixed resistor of 0 kΩ is provided, and a fixed resistor 1 of the integrator 11 is provided.
The resistance value of 1c is 100 kHΩ, and the fixed resistor 11
and a fixed resistor of 100 kΩ between c and the operational amplifier 11a.
A noise filter including a 7 pF capacitor is provided.

In this configuration, when the input Y was kept constant at 5 mV and the division input E was changed within the range of 5 to 100 mV, the division characteristic as shown in FIG. 6 was obtained. In this figure, the horizontal axis is the normalized divisor, which is E / Y. When the divisor coefficient was obtained from this figure, it was found to be approximately 1.057 as shown in FIG. As a result, FIG.
It can be seen that the linear divider shown in FIG.

[0088]

[Equation 9]

Further, the division gain deviation when the gain is changed over 20 times is obtained as shown in FIG.
This deviation was within ± 3%.

FIG. 9 is a diagram in which the linear divider shown in FIG. 3 is applied to the specific example shown in FIG. 2, 17 is a low voltage source, and the portions corresponding to FIGS. Attached.

In the figure, the voltage generated in the fixed resistor 3 on the secondary side of the photocoupler 2 corresponds to the input X in FIG. 3, and the AC voltage XAC of this input X is stored in the capacitor 4.
Is extracted and is fed as a multiplication input through the fixed resistor 12 to F
It is supplied to the source S of the ET 10. The voltage generated in the fixed resistor 3 is supplied to the direct-current detector 5, the direct-current voltage E is extracted, and the direct-current voltage E is extracted through the inductor 15 and the fixed resistor 12 to F.
It is supplied to the source S of the ET 10. DC detector 5
For example, an integrator is used. Input Y as reference voltage supplied to operational amplifier 11a of integrator 11
Is supplied from the low voltage source 17.

According to this configuration, as described with reference to FIG. 3 and the like, the division processing with low power consumption and high precision is performed, and the AC of the input A is applied to the output terminal 7 regardless of the variation of the current transfer rate CTR of the photocoupler 2. An output signal ZAC (AC voltage of the output Z) having a level proportional to the input signal which is the voltage VAAC is obtained.

FIG. 10 shows an optimized compensation circuit for the light receiving element shown in FIG. 9, which is more practical, that is, in the compensation circuit shown in FIG. 2, AC extraction and DC extraction are performed by separate circuits. Is a circuit diagram optimized by omitting a functionally overlapping portion. Reference numeral 14 'is a constant voltage source, and portions corresponding to FIG. 9 are denoted by the same reference numerals.

In the figure, the light receiving element 2b of the photocoupler 2 is directly connected to the source of the FET 10, and a DC voltage E'is supplied from the constant voltage source 14 'to this light receiving element 2b. The configuration other than this is the same as the specific example shown in FIG.

In this specific example, the internal resistance of the light receiving element 2b is used as the fixed resistor 3 in FIG. 9, and this internal resistance and the variable resistance of the FET 10 are used as a voltage divider (attenuator).
And the integrator 1 as in the specific example shown in FIG.
The FET 10 is servo-controlled so that the DC voltage ZDC of the output Z obtained at the output terminal 7 by the action of 1 becomes equal to the reference voltage Y.

FIG. 11 shows the experimental results of the fluctuation of the signal voltage ZAC at the output terminal 7 with respect to the change of the current transfer rate CTR of the photocoupler 2 in this specific example. The solid line shows the result, and the broken line shows the fluctuation of the output signal voltage of the photocoupler 2 when the compensation is not performed as in this specific example.

Since it is very difficult to use samples of photocouplers having different current transfer rates as the experimental method, the primary side of the photocoupler 2 (light emitting element 2a side)
Is provided with a means for varying the primary current, and the AC voltage VAAC of the input A is set to a constant amplitude, and the primary current is sequentially changed.
It is assumed that R changes and the amplitude of the signal voltage ZAC at the output terminal 7 is measured.

As a result of this experiment, even if the primary current of the photocoupler 2 is changed ten times as shown by the solid line A in FIG.
The amplitude of the output signal voltage ZAC was almost constant. On the other hand, when such a compensation is not performed and a similar experiment is performed with the voltage generated in the fixed resistor 3 in FIG. 9 as the output signal voltage, the output signal voltage is proportional to the change in the primary current. Therefore, it becomes as shown by the broken line B in FIG.

FIG. 12 shows changes in the output signal voltage with respect to changes in the relative value of the current transfer rate CRT of the photocoupler from the results for the specific example of FIG. 11, and according to this, 10% of the current transfer rate CRT of the photocoupler is obtained. The fluctuation of the output signal voltage was about ± 5% with respect to the double fluctuation range.

As described above, also in this specific example, a substantially constant output signal voltage can be obtained without being affected by the variation in the current transfer rate CRT of the photocoupler.

FIG. 13 is a block diagram showing a line interface section of a modem using a photocoupler having the above compensation circuit.

The configuration of the modem of this specific example is the same as that shown in FIG. 17, but the line interface section is shown in FIG.
It has the configuration shown in FIG. That is, the transmission side is provided with a transmission amplifier, a transmission photocoupler, and a gain compensation circuit thereof, and this gain compensation circuit is the compensation circuit of the photocoupler 2 described above. The transmission photocoupler is connected to the modulation / demodulation unit in FIG. 17 via the transmission amplifier. Further, a receiving photocoupler is provided on the receiving side, and this is connected to the modulation / demodulation unit in FIG. 17 via a receiving amplifier (not shown). Further, the transmission photocoupler and the reception photocoupler are connected to a telephone line, which is a two-wire type line (not shown), through a resistance bridge.

FIG. 14 is a diagram showing the circuit configuration of the line interface section shown in FIG. 13. Reference numeral 104 is the compensation circuit described above, and the parts corresponding to those in FIG. 18 are designated by the same reference numerals. .

In the figure, as described above, the transmission power is transmitted through the transmission photocoupler 100 without being affected by the current transfer rate of the photocoupler 100 by the compensation circuit 104, and the AC current loop transmission amplifier 106 and It is sent to the telephone line 103 through the 4-terminal bridge 102.
Therefore, by appropriately setting the transmission power on the transmission side,
It is possible to stably transmit electric power so as to satisfy the maximum transmission electric power specified by the Telecommunications Business Law.

Further, the modem can be sufficiently miniaturized, insulation from the telephone line can be sufficiently achieved, and a thin card that conforms to the PCMCIA / JEIDA TYPE 1 standard can be realized.

A similar compensating circuit 105 may be provided on the secondary side of the receiving photocoupler 101 so that the received signal is not affected by the current transfer rate of the receiving photocoupler 101.

In FIG. 14, the compensation circuits 104 and 105 shown in FIG. 10 are applied, but the compensation circuit shown in FIG. 1 can be applied as shown in FIG. The same effect as the face part can be obtained.

In the line interface section of FIG. 15, the input terminal X in FIG. 16 is connected to the X terminal and the Y terminal is connected to the output terminal Y in FIG.
2-wire system, 3-wire system or 4 between terminals Z2 and Z1 at
A communication terminal such as a line type mobile phone or a facsimile can be connected, and communication between the modulation / demodulation unit as shown in FIG. 17 and the communication terminal becomes possible.

That is, the signal from the modulation / demodulation unit is input from the input terminal X in FIG. 16, passes through the emitter follower of the transistor 108, and from the terminal Z2 to the communication terminal 1 described above.
09. Therefore, when the communication terminal 109 is a mobile phone, the signal from the modulation / demodulation unit in FIG. 17 is communicated to the other party via the mobile phone. Also, a signal is output from the communication terminal to the terminal Z1 and the base-grounded transistor 1
It is sent from the output terminal Y to the terminal Y of FIG.
It is sent to the modulation / demodulation unit in FIG.

If the communication terminal 109 is a two-wire system, its input terminal is the terminal Z2 and its output terminal is the terminal Z.
1 is connected to each. When a signal is input from the input terminal X, the grounded-base transistor 107 has a very low input impedance, so that a ground path is formed from the terminal Z1 through the transistor 107 and the power supply.

When the communication terminal 109 is a four-wire type, its input side is connected to the terminal Z2 and the ground terminal, and its output side is connected to the terminal Z1 and the ground terminal. When the input side or the output side of the communication terminal 109 is a three-wire type having two wires, the input side is connected to the terminal Z2 and the ground terminal,
Its output side is connected to the terminal Z1 or its input side is connected to the terminal Z2 and its output side is connected to the terminal Z1 and the ground terminal.

In the above specific example, the case where the present invention is applied to a modem has been mainly described, but the present invention is not limited to this, and an analog signal is transmitted via a photocoupler, for example. It is applicable to general electronic devices such as telephones, VTRs, television receivers, and facsimiles.

Further, it can be applied to a communication line using an optical fiber as the optical coupling communication path, and the difference in loss due to the difference in the length of the communication path can be eliminated.

[0114]

As described above, according to the compensation circuit for a light receiving element according to the present invention, a signal is transmitted at a constant level through the photocoupler without being affected by the variation in the current transfer rate of the photocoupler. Is possible.

Further, according to the modem of the present invention, even if a photocoupler is used in the line interface section to connect to a telephone line, a transmission signal with stable transmission power can be sent to the telephone line, and adjustment work can be performed. It is possible to omit it, and it is possible to reduce the size and thickness of the card and to make it into a card as a whole.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a first specific example of a compensation circuit for a light receiving element according to the present invention.

FIG. 2 is a block diagram showing a second specific example of a compensation circuit for a light receiving element according to the present invention.

FIG. 3 is a circuit diagram showing a specific example of the divider in FIG.

FIG. 4 shows the source for the control voltage at the FET.
FIG. 6 is a characteristic diagram showing changes in resistance and impedance between drains.

5 is a circuit diagram showing a more specific configuration of the divider shown in FIG.

6 is a diagram showing a division characteristic of the specific example shown in FIG.

7 is a diagram showing division coefficients obtained from the characteristics shown in FIG.

8 is a characteristic diagram showing a gain deviation of the specific example shown in FIG.

9 is a circuit diagram showing a configuration when the divider shown in FIG. 3 is applied to the specific example shown in FIG.

FIG. 10 is a circuit diagram showing a third specific example of a compensation circuit for a light receiving element according to the present invention.

11 is a diagram showing experimental results of changes in output signal voltage with respect to the primary current of the photocoupler in the specific example shown in FIG.

FIG. 12 is a diagram showing changes in the output signal voltage with respect to the current transfer rate of the photocoupler based on the experimental results shown in FIG.

FIG. 13 is a configuration diagram showing a main part of a first specific example of a modem according to the present invention.

14 is a circuit diagram showing a circuit configuration of the specific example of FIG. 13 to which FIG. 10 is applied.

15 is a circuit diagram showing a circuit configuration of the specific example of FIG. 13 to which FIG. 1 is applied.

16 is a circuit diagram showing a specific example of means for connecting a communication terminal to the modem shown in FIG.

FIG. 17 is a diagram showing a configuration of a modem.

FIG. 18 is a circuit diagram showing a conventional example of a line interface section in a modem.

FIG. 19 is a characteristic diagram of the current transfer rate of the photocoupler.

FIG. 20 is a characteristic diagram showing power supply voltage dependence in a saturation region of a light receiving element.

FIG. 21 is a characteristic diagram showing power supply voltage dependence in an unsaturated region of a light receiving element.

FIG. 22 is a characteristic diagram showing a relationship between collector-emitter voltage and collector current.

FIG. 23 is a characteristic diagram specifically showing an operating point in the unsaturated region of the light receiving element.

[Explanation of symbols]

 1 voltage / current converter 2 photocoupler 2a light emitting element 2b light receiving element 3 fixed resistor 4 capacitor 5 direct current detector 6 divider 7 output terminal 8, 9 input terminal 10, 10a, 10b, 10c FET 11 integrator 11a operational amplifier 11b Capacitor 11c Fixed resistor 12 Fixed resistor 13 Capacitor 14 Voltage source 15 Inductor 16 Output terminal 100 Transmission photocoupler 101 Reception photocoupler 102 Resistance bridge 103 Telephone line 104, 105 Compensation circuit for light receiving element 106 AC current loop transmission amplifier 201 Voltage Current converter 202 Photocoupler 202a Light emitting element 202b Light receiving element 203 Fixed resistor 204 Transistor 205 Integrator 206 Constant voltage source 207 Power supply 208 Input terminal 209 Output terminal

Claims (9)

[Claims] 1. A conversion gain control circuit for controlling the conversion gain of a light receiving element, the circuit being a phototransistor which operates in an unsaturated region, or a phototransistor in which a grounded-emitter transistor amplifier is connected to the rear side. A light receiving circuit comprising: a light receiving element composed of a diode; and a light receiving element operating point control circuit for controlling an operating point so that the light receiving element operates in an unsaturated region of a low voltage. 2. The light receiving circuit according to claim 1, wherein the light receiving circuit is a circuit used in a photocoupler or an optical coupling communication system. 3. The light receiving element operating point control circuit according to claim 1, wherein the operating point of the light receiving element is changed by adjusting the ratio of the voltage across the light receiving element and the flowing current. A light receiving circuit characterized in that. 4. The feedback according to claim 2, wherein the light receiving element operating point control circuit includes a resistor, an integrator, and a transistor, and the photo coupler or the light receiving element of the optical coupling communication system, the resistor, the integrator, and the transistor. It has a loop, the transistor is cascode-connected to the light receiving element, the base terminal of the transistor is connected to the output side of the integrator, and the operating point of the light receiving element is that the value of the direct current flowing through the light receiving element is Feedback control is performed so that the reference voltage is the value divided by the resistor value, and the light receiving element operates in the unsaturated region, and the primary side DC current and the secondary side DC current are made constant. , The direct current transfer function is constant, and the absolute value of the alternating transfer function is almost equal to the direct current transfer function. Light receiving circuit, wherein the transfer function of the side is configured to be substantially constant. 5. A light-receiving circuit including a light-receiving element that receives light from a light-emitting element that is current-driven by a signal and outputs a current according to the amount of received light, and extracts the AC component of the output signal of the light-receiving element. AC extraction means, a DC extraction means for extracting the DC component of the output signal of the light receiving element, and a division means for dividing the AC component by the DC component are provided, and the AC extraction means and the DC extraction means are divided. By means of
A light receiving circuit, which is configured to compensate for variations and fluctuations in the output of the light receiving element with respect to the drive current of the light emitting element. 6. The source of the field effect transistor according to claim 5, wherein the dividing means is supplied with an output signal of the light receiving element, is supplied with a field effect transistor operating in a variable resistance region, and is supplied with a constant reference voltage. A source of the field effect transistor, comprising an integrator for integrating a difference between the DC voltage obtained between the drains and the reference voltage, and supplying the output of the integrator as a control voltage to the gate of the field effect transistor; Servo is applied so that the DC voltage obtained between the drains and the reference voltage are equal to obtain an output obtained by dividing the AC signal of the light receiving element by the DC signal of the light receiving element from the source of the field effect transistor. A light receiving circuit characterized by being configured. 7. The light receiving circuit according to claim 5, wherein the light receiving circuit is a circuit used in a photocoupler or an optical coupling communication system. 8. A modem for performing communication via a telephone line, wherein the modem is connected to the telephone line via a photocoupler having the light receiving circuit according to any one of claims 1 to 6. modem. 9. An optical communication device for performing communication by exchanging optical signals, comprising the light receiving circuit according to any one of claims 1 to 6.