JPH0697404A - Optical receiving device - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide an optical receiving device that achieves both high-speed operation and simplification of the device. A photodiode 1 for converting an optical signal 3 into an electric signal, a forward-polarity diode 2 as a load element connected to the output side of the photodiode 1, and a connection between the photodiode 1 and the diode 2 A comparator 6 for comparing the voltage of the node and the voltage of the reference voltage source 5 and outputting a digital signal is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical receiver, and more particularly to an optical receiver for digital optical transmission intended for short distance transmission.

[0002]

2. Description of the Related Art Long-distance, large-capacity optical transmission using an optical fiber is positioned as an important technique for trunk line communication because it can obtain a distance band product characteristic that is difficult to realize in telecommunication. In such optical transmission technology, the performance of each device and parts,
Since long-term reliability is emphasized, we make full use of all technologies to ensure performance. Therefore, the device and parts are much more expensive than general electronic parts and modules, and the technical application thereof is limited to a very small part of a very large scale system.

Optical transmission is superior to electrical transmission in terms of resistance to electromagnetic interference and broadband characteristics. In addition to long-distance, large-capacity transmission, relatively low-speed (low-capacity), short-distance applications are possible. It is also used in. For example, there are control wiring for machine tools and digital wiring for audio equipment. In this case, considering that the transmission speed is relatively slow, the transmission / reception device configuration is simplified, and by thoroughly reducing the price of materials, parts, etc., the price is the same as that of general electronic parts. The band has been realized, and a relatively wide range of technological applications are possible.

As a typical example of the above-mentioned optical transmission performance of long distance / large capacity and short distance / low capacity, the former is 10 Gbps.
・ 100km and the latter is 20Mbps ・ 4km, which is more than 10,000 times the price. in this way,
In the current optical transmission technology, bipolar areas of high performance or low price have been developed, and areas of performance that conform to the former and price of the latter have not been developed so much.

This intermediate area can be said to be important in the fields of information processing, image processing, exchange, etc., and in particular, there is a growing demand for wiring between boards of high-speed information equipment such as ultra-high speed computers and exchanges of asynchronous signal transfer system. ing. In such a field, a performance of a relatively short distance at a transmission speed of about 1 Gbps is good, but the number of connections is very large, so that a drastic reduction in price is required. With the current technology, the price cannot be followed when the performance is satisfied, and the performance cannot be followed when the price is satisfied.For example, in the trunk optical transmission device, a simple mass production effect can significantly reduce the price due to the complexity of the device configuration. I can't expect.

Further, in the information device in the intermediate area, as described above, a large number of wirings are required, so that the mounting area required for the signal wiring device must be minimized. That is,
In this type of information device, high-speed signal connection in the device is several hundreds to
Thousands are required, and in some cases, the number of connections is tens of times more. Therefore, in these optical transmission technologies,
In addition to cost reduction, it is necessary to simplify the structure of the device, that is, to reduce the number of parts used to reduce the size of the device, and on top of that, it is necessary to ensure high-speed transmission operation. Of course, integration of used parts, for example, OEIC
(Opto-Electoronic IC) and the like can be expected to be effective for that purpose, but it is desirable that the basic transmission and reception cells are essentially simplified.

A technique effective for such a demand is disclosed in, for example, Japanese Patent Application No. 62-166907. This document describes a method for fundamentally simplifying the drive circuit of a semiconductor laser used as a high-speed light emission source used on the transmission side. Considering the type and characteristics of the semiconductor laser, set appropriate operating conditions. The optical output monitor and an output stabilizing circuit using the optical output monitor, so-called APC (Automatic Power C
ontrol) circuit is disclosed.

According to this technique, the semiconductor laser, which is a high-speed light emitting source, is basically stabilized independently of the external control circuit, and stable operation is ensured by simply providing the signal / current exchanger as a buffer. This signal / current exchanger
It can be configured with a simple transistor circuit, and depending on the current level, it can be configured with only one resistance element.

Since a high-speed light emitting source is a semiconductor laser, the light emitting operation in the optical transmitter is not limited by the carrier life time unlike a light emitting diode, and an operation of about 1 Gbps can be performed relatively easily. .

However, with respect to the optical receiving device, such a promising technique has not been found, and either a high speed operation with a complicated structure or a simple structure with a relatively low speed operation is adopted. In order to operate at about 1 Gbps, it is necessary to use an amplifier having a large gain band product, which requires an optical receiving device having a relatively complicated configuration. The specific contents will be described below with reference to the drawings.

FIG. 15 is a diagram showing a circuit configuration of a conventional optical receiving device. In the figure, 91 is a photodiode as a light receiving element, and a load resistor 92 is connected to the output side thereof. A preamplifier (front end amplifier) 93, a postamplifier 94, and a discriminator 97 are connected in series between the photodiode 91 and the load resistor 92. A level detector 95 is connected to the output side of the post amplifier 94, and its output is input to the post amplifier 94. Furthermore, on the output side of the post amplifier 94,
The clock extraction circuit 96 is connected, and its output is the discriminator 9
It is designed to be input to 7. The output of the photodiode 1 includes the electrical / optical conversion efficiency on the transmission side and the optical coupling efficiency to the transmission line, the transmission efficiency on the transmission line, the optical coupling efficiency and the optical / electrical conversion efficiency on the reception side.

The output current of the photodiode 91 due to the optical signal 90 flows through the load resistor 92 and is converted into a voltage signal. At this time, if the resistance value of the load resistor 92 is too large,
Since the high-speed response is limited by the parasitic capacitance of the photodiode 91, the resistance value is set to be relatively small. Therefore, the amplitude of the converted voltage signal is often very small. The voltage signal of this minute amplitude is stepwise amplified in an analog state by the preamplifier 93 and the postamplifier 94, and in some cases, a waveform equivalent amplifier (equalizer amplifier) is used for the postamplifier 94 so as to be asymptotic to the appropriate signal waveform. Is amplified. Then, the amplified signal is monitored by the level detector 95 and the amplification factor of the post amplifier 94 is automatically adjusted (Automatic Gain Control) so that the input signal to the next stage maintains an appropriate level. After this, the discriminator 9
The output signal of the post-amplifier 94 is set to "1" or "0" by 7
The digital signal is reproduced by performing the digital judgment of (1). At this time, the clock signal for determining the signal judgment timing is generated by the clock extraction circuit 96.

By such a series of operations, the fluctuation of the transmission level due to the switching of the transmission path and the temperature fluctuation is absorbed, so that the voltage signal converted by the load resistor 92 is stable even when it is weak or relatively large. Then, digital signal reproduction can be performed. According to such a circuit, the input dynamic range is 20 to 30d.
B is secured.

FIG. 16 is a diagram showing a circuit configuration of another conventional light receiving device.

In this light receiving device, as shown, a load resistor 92a and a preamplifier 93a are connected in parallel to perform active current / voltage conversion. This is an example using a so-called transimpedance type light receiving circuit. This light receiving device is characterized in that the potential change due to the load resistance 92a is not fed back to the photodiode 91, and the load characteristic ideal for the photodiode 91, that is, the input impedance is extremely small. Therefore, the linearity of the output of the photodiode 91 is improved even when the input signal is relatively large.

The conventional optical receiving device configured as shown in FIGS. 15 and 16 can realize good receiving characteristics even at high speed operation.

However, the preamplifier 93, the postamplifier 94, the level detector 95, and the clock extraction circuit 9
6. Since the discriminator 97 is composed of a complicated circuit, the entire device has a complicated structure. Also, since the ratio of the portion that operates in analog is high, the reception characteristics are gain adjustment, S /
It is greatly influenced by the N ratio. For this reason, it is difficult to simplify the configuration while maintaining high-speed operation, and it is difficult to reduce the cost and size, and thus it is difficult to form an array of devices such as parallel optical transmission.

[0018]

As described above, the conventional optical receiving device has a complicated structure and a high ratio of analog operating parts. Therefore, there is a problem that it is difficult to simplify the configuration while maintaining the high speed operation of the optical receiving device.

The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide an optical receiving apparatus that achieves both high-speed operation and simplification of the apparatus.

[0020]

The essence of the present invention is to use a forward polarity diode as a load element of a light receiving element for converting an optical signal into an electric signal.

In other words, in order to achieve the above-mentioned object, an optical receiving device (Claim 1) of the present invention includes a light receiving element for converting an optical signal into an electric signal and an electric signal output from the light receiving element. And a diode connected to the output side of the light receiving element and an output terminal provided between the diode and the light receiving element so as to be in the forward direction.

Further, another optical receiving apparatus of the present invention (claim 2) is a light receiving element for converting an optical signal into an electric signal, and a resistance element connected in parallel with the electric signal output from the light receiving element. It is characterized by comprising a diode connected to the output side of the light receiving element and an output terminal provided between the diode and the light receiving element so as to be in the forward direction with respect to the signal.

Further, another optical receiving apparatus of the present invention (claim 3) is such that a light receiving element for converting an optical signal into an electric signal and a forward direction with respect to the electric signal outputted from the light receiving element. , A diode connected to the output side of the light receiving element, an output terminal provided between the diode and the light receiving element, a voltage at the output terminal and a reference voltage are applied, And a comparator that outputs a high-voltage or low-voltage electrical signal.

It is desirable to use a Schottky barrier type diode as the diode.

[0025]

In the optical receiver of the present invention (claim 1), a forward polarity diode is used as the load element of the light receiving element.
Therefore, even if the output current of the light receiving element largely changes, the change in the voltage drop due to the diode, that is, the change in the amplitude of the output signal at the output terminal is small, and in addition, the amplitude of the output signal is large.

If the change in the amplitude of the output signal is small, the circuit in the next stage only needs to be able to cope with the amplitude in a narrow range, so that the structure of the circuit in the next stage can be simplified. Further, if the amplitude of the output signal is large, the amplifier circuit becomes unnecessary. For this reason, the configuration is simpler than in the conventional case, and the ratio of the portion that performs analog operation can be reduced, so that the configuration of the optical receiving device can be simplified while maintaining high-speed operation.

Further, in another optical receiver of the present invention (claim 2), a forward polarity diode and a resistance element connected in parallel are used as a load element. For this reason, an optical receiving device that operates at high speed and has a simple structure can be obtained, and in addition, the self-bias effect can be suppressed, and thus the level margin for noise can be significantly improved.

Further, in another optical receiving apparatus of the present invention (claim 3), the voltage of the output terminal and the reference voltage are applied, and an electric signal of high voltage or low voltage is output according to the difference between these voltages. A comparator is provided. Therefore, it is possible to obtain the optical receiving device which operates at high speed and has a simple structure, and in addition to that, it is possible to perform the digital receiving operation from the beginning.

If a Schottky barrier type diode is used as the diode, it is possible to prevent a reduction in high-speed operation due to the effect of accumulating minority carriers inside the diode.

[0030]

Embodiments will be described below with reference to the drawings.

FIG. 1 shows a circuit configuration of an optical input section of an optical receiver according to an embodiment of the present invention.

In the figure, 1 is a photodiode which is a light receiving element for converting the optical signal 3 into an electric signal. The cathode of the photodiode 1 is connected to the power supply potential V _B. Between the anode and the ground photodiode 1, forward polarity diode 2 for converting the output current I _P of the photodiode 1 to the voltage is provided.
The diode 2 may be a pn-junction type diode, but has a high degree of freedom in setting the rising voltage and excellent temporal response characteristics (because the reduction in high-speed operation due to the minority carrier accumulation effect inside the diode can be eliminated). It is preferable to use a key barrier type diode (hereinafter, also referred to as SBD). An output terminal 4 is provided at a connection node between the photodiode 1 and the diode 2.

Next, the static characteristics of the light input portion configured as described above will be described when the SBD is used as the diode 2.

The device current I _F of the diode 2 which is forward biased can be expressed by the following equation.

I _F = SA ^* T ² EXP (−eφ _B / kT) {EXP (eV _F / nkT) −1} (1) where S is the junction area, A ^* is the Richardson constant, and T
Is temperature, e is electron charge, φ _B is junction barrier height, k
Is the Boltzmann constant, V _F is the junction potential difference, and n is the diode constant.

The formula (1) is modified to obtain the inverse function of V _F as follows.

V _F = (nkT / e) · ln {(I _F / SA ^* T ² ) EXP (eφ _B / kT) +1} (2) This equation (2) is for the device current I _F. Junction potential difference V _F
Means to change logarithmically. That is, the output voltage V _o of the output terminal 4 changes logarithmically with respect to the output current I _{P of the} photodiode 1.

Assuming that the photodiode 1 is sufficiently biased, the power of the optical signal 3 (hereinafter, also referred to as optical input power) is P _IN , the photon energy of the optical signal 3 is hν, and the photodiode 1 is the absorption coefficient of internal α of the output current I _P in the case where the absorption layer thickness is W _{is, I P = (e / hν} ) {1-EXP (-αW)} P iN ... (3) and expressed.

As an example, when GaInAs lattice-matched to InP is used as an absorption layer, α at a wavelength of 1.3 μm is about 10000 cm ⁻² , and when W is 3 μm, the following approximate relational expression is obtained. Is obtained.

I _P ˜0.996 _{P IN} (4) Therefore, the output voltage V _{o at} this time is as follows.

V _o = (nkT / e) · ln {(0.996P _IN / SA ^* T ² ) EXP (eφ _B / kT) +1} (5) In FIG. 2, as SBD, on n-type InP The relationship between the optical input power P _IN and the output voltage V _o when an element made of Au is used is shown. The bonding diameter of SBD is 10 μmφ.
Further, the relationship between the optical input power and the output voltage of the conventional optical input section using a resistor of 23.5 kΩ as the load resistance is also shown by a chain double-dashed line.

From this figure, in the case of this embodiment, when the optical input power P _IN changes to 0 μW, 2 μW and 20 μW, the output voltage V _o changes to 0 V, 0.47 V and 0.56 V, and the optical input power P _IN changes. It can be seen that even if _IN changes 10 times, the change in output voltage V _o is 20% or less.

On the other hand, in the case of the conventional optical input section, when the optical input power changes to 0 μW, 2 μW and 20 μW, the output voltage changes to 0 V, 0.056 V and 0.56 V, and the optical input power changes 10 times. The output voltage changes about 10 times.

Therefore, when the conventional optical input section is used, it is necessary to use an analog amplifier circuit capable of amplifying to a predetermined level over a wide range of input voltage as an amplifier of the next stage. It is inevitable that it will be complicated and that operation speed will be delayed.

On the other hand, when the optical input section of this embodiment is used, the range of the input voltage to be amplified is narrow and the input voltage is large, so that the amplifier circuit having a simple structure can be used. The device can be simplified while maintaining high-speed operation. For example, the appropriate input voltage range of the amplifier circuit of the next stage is 0.
Assuming 5 ^{± 0.1} V, a fixed gain amplifier circuit can be used at least when the optical input power is in the range of 1 to 100 μW. This value is the AGC of the conventional optical receiver of FIG.
Equivalent to a dynamic range of 20 dB.

As described above, according to the present embodiment, it is possible to realize a function equivalent to that of an AGC circuit having a complicated structure while maintaining a high speed operation while having a very simple structure.

Further, by simplifying the basic structure, it is possible to realize an array of devices, reduce the production cost of the devices, and reduce the size of the device. Moreover, since the analog amplifier is omitted, the power consumption is remarkably reduced, the circuit design is easy, and the adjustment for each device is almost unnecessary. Due to such characteristics, the optical receiving device of the present embodiment can be used as an optical transmitting device for a high speed information device having a relatively short transmission distance.

In actual circuit connection, for example, an element such as FET may be used as a buffer element, and an appropriate DC bias shift may be given to adapt it to various logic circuit levels.

In the above description, the ideal photodiode 1 is assumed to be described, but since there is actually an output current (dark current I _D ) in a no-input state, it is necessary to consider this influence. is there. As the value of this dark current, the above-mentioned G
Approximately 1 for aInAs / InP junction diameter of 50 μmφ
Although it is a value of about nA, this value changes greatly due to temperature fluctuations. When the relationship between the dark current I _D and the temperature T is expressed by an equation, I _D = I _DO EXP (−eE _G / kT) (6) Note that E _G is the energy gap of the photodiode.

From this equation (6), it can be seen that the dark current _ID changes exponentially with temperature.

Since the present invention utilizes the non-linear characteristic of the diode, there is a characteristic that even a slight dark current I _D easily contributes to the output voltage V ₀ . Therefore, it is assumed that the output voltage change (dark current drift) at the “0” level occurs exponentially. However, in practice, dark current drift is automatically suppressed without special design consideration. This is explained as follows.

The "0" level output voltage V _D is obtained by substituting the dark current I _D in (6) for the output current I _P in the equation (2) and rewriting the junction potential difference V _F as the output voltage V _D. Then, V _D ˜ (nkT / e) ln [(I _DO / SA ^* T ² ) · EXP {e (φ _B −E _G ) / kT} +1] (7) is approximately represented.

This expression (7) shows that the output voltage V _D at the “0” level changes in proportion to the temperature change, and when it is developed approximately, n (φ
It can be seen that there is an offset voltage corresponding to the _B -E _G).

This state is shown in FIG. In the case of the photodiode 1 described above, the dark current _ID is 4 pA at -20 ° C,
It becomes 70 nA at 80 ° C. and changes about 20000 times, but as can be seen from this figure, the quiescent voltage V _D is 0.2.
It only changes about 1.5 times from V to about 0.3V.

Therefore, since the quiescent voltage is relatively stable with respect to temperature changes, the dark current I _{D of the} photodiode 1 and the zero level shift bias or digital signal corresponding to the device parameters (φ _B , E _G ) are used. There is no practical problem if the threshold value is set.

FIG. 4 shows an example of a specific element structure of the light input section shown in FIG.

In the figure, 11 is an n-type InP semiconductor substrate, on which the n-type InP buffer layer 12 and GaI are formed.
An nAs light absorption layer 13 and an n-type InP window layer 14 are sequentially provided. n-type InP window layer 14 to G
A Zn diffusion region (p-type InP window layer 14) 16 is formed on the surface of the aInAs light absorption layer 13.

On the surface of the Zn diffusion region 16, a Schottky electrode 17 and an output electrode 18 in ohmic contact for extracting a signal are provided. The Schottky electrode 17 is, for example, an Au / Pt / Ti laminated electrode in which Ti contacts the Zn diffusion region 16, and the output electrode 18 is, for example, A in which Zn contacts the Zn diffusion region 16.
A u / Pt / Ti / Zn laminated electrode may be used.

The surfaces of the n-type InP window layer 14 where the Schottky electrode 17 and the output electrode 18 are not provided and the Zn diffusion region 16 are covered with a passivation dielectric film 15 made of a silicon nitride film or the like.

On the other hand, on the back surface of the n-type InP semiconductor substrate 11, a low reflection coating film 19, n for introducing the optical signal 3 is formed.
A type ohmic electrode 20 is provided. For example, a silicon nitride film may be used as the low-reflection coating film 19, and an AuGe electrode may be used as the n-type ohmic electrode 20, for example.

In the device thus constructed, the Schottky electrode 17 is connected to the ground potential and the n-type ohmic electrode 2 is used.
When 0 is connected to the power supply potential V _B (positive bias), a photodiode is formed between the output electrode 18 and the n-type ohmic electrode 20, and the Schottky electrode 17 and the output electrode 1 are connected.
8 forms an SBD between them and the output voltage V ₀ can be taken out from the output electrode 18 serving as the output terminal 4.

Since the optical input section of this embodiment has a simple structure, it can be easily integrated by building an SBD in a normal photodiode.

In the light input section of FIG. 1, n-type InP is used as the semiconductor of the SBD, but here, the SBD is used.
An example in which p-type InP is used as the semiconductor is shown. This is because of the simplicity of the configuration, and n-type InP may be used as the semiconductor of the SBD. The difference between n-type and p-type semiconductors appears in the polarity on the metal side and in φ _B in equation (1).
The level of the output voltage of the SBD changes depending on _B. vice versa,
By using this, the output voltage level can be adjusted to the logic circuit by changing the output polarity, the impurity concentration of the p-type or n-type semiconductor, and the type of metal.

FIG. 5 shows a circuit configuration of an optical input section for directly receiving digital light using such an element. In the figure, the photodiode 1 within the chain line and the diode 2 for load resistance
Indicates that element integration as shown in FIG. 4 is being performed. Further, 6 is a comparator, which compares the reference voltage from the reference voltage source 4 with the output voltage of the output terminal 4 and outputs a digital signal of "0" or "1". To do.

At this time, assuming that the output voltage of the output terminal 4 has the characteristic as shown in FIG. 3, for example, if the reference voltage of the reference voltage source 5 is set to 0.35 V, the influence of the zero input will occur. Can be removed, and 1 to 10 in the range of -20 ° C to 80 ° C.
A signal of 0 μW can be received. In addition, the threshold uncertainty width at this time can be secured at a minimum of 50 mV or more, and the noise resistance is relatively problematic.

In this way, the analog circuit portion in the digital optical receiver is omitted as much as possible, and even if the optical signal 3 is a weak signal, the optical signal 3 is basically a digital signal. Photodiode 1 to convert to electric signal
By using the forward polarity diode 2 as the load element of and the non-linear characteristic of the current-voltage characteristic of the diode 2 is used, the digital receiving operation can be performed from the beginning.

Next, the dynamic characteristics of the light input section of FIG. 1 will be described. The dynamic characteristics of the optical input part are not only the current / voltage characteristics of the diode 2 (SBD in this case) as a load resistance, but also the frequency axis response that takes into account the junction capacitance and differential resistance of the SBD and the parasitic capacitance of the photodiode 1. Or it is necessary to consider the time base response.

When the signal amplitude is relatively small, the DC current level can be fixed and each parameter can be approximated by an equivalent linear element, and the response limit can be considered on the frequency axis. Here, _assuming that the direct current component of the signal current is I _PO and the output voltage at that time is V _o , the junction capacitance C _S and the differential resistance R _S are as follows.

C _S (V _o ) = S {C _S (0) ^−1/2 −aV _o } ^−1/2 (8) R _S (I _PO ) = nkT / e [I _P + SA ^* T ² EXP (−eφ _B / kT)] (9) In the expression (8), a is a coefficient representing the voltage dependence of the junction capacitance.

When the photodiode parasitic capacitance is C _P , the response limit frequency f _C when the signal amplitude is small is expressed as follows using the junction capacitance C _S and the differential resistance R _S.

F _C = 1 / [2π {C _P + C _S (V _o )} R _S (I _PO )] (10) Here, considering that V _o is determined by I _PO , f _C
It can be seen that is determined by I _PO .

According to the equations (8) to (10), the larger the signal, the faster the response can be made, and conversely, the smaller the signal, the lower the response limit. This means that when considering a relatively large pulse signal response, the rise of the signal (large current) is steep,
It means that the trailing edge of the pulse (small current) is easy to pull.

FIG. 6 shows the photodiode and S described above.
The time response characteristic at the time of using BD is shown. Here, 1
The characteristics are shown when an optical clock pulse of 0 Mbps is input.

As can be seen from FIG. 6, the rising edge of the pulse is fairly fast, but the trailing edge is tailed as the output decreases. Also, this allows the tail of the previous pulse to reach the next pulse, and the self-biasing effect of the quiescent level will occur during continuous operation.

However, by using the optical input section of FIG. 5 instead of the optical input section of FIG. 1, it is possible to eliminate the influence of such self-bias effect.

That is, if the reference voltage of the reference voltage source 5 of the optical input section of FIG. 5 is set to be higher than the self-bias, the influence of the self-bias effect can be eliminated.
By setting to 1, digital reception of 100 Mbps or more is possible. Also, set the minimum value of the optical input power to 1
When it is set to 0 μW or more, by setting the reference voltage to 0.45 V, digital reception of 500 Mbps or more is possible.

As described above, according to the optical input section of FIG. 5, although the configuration is greatly simplified, the optical input section of FIG. 15 is used without using the analog amplifier, the AGC circuit, the clock extraction circuit, and the like. Like the conventional high-impedance type optical input section, it is possible to receive a digital optical signal. Such an optical input unit is effective in constructing an arrayed optical transmission device because it can be easily downsized and reduced in cost by integrating device parts, and thus can also be used in a two-dimensional array of optical transmission. This makes it possible to realize a large-capacity high-speed signal bus in a device that is difficult to make by electrical connection.

FIG. 7 shows a circuit configuration of an optical input section of an optical receiver according to another embodiment of the present invention. Note that the portions corresponding to the light input portion of FIG. 5 are denoted by the same reference numerals as those in FIG. 5, and detailed description thereof will be omitted.

This optical input section corresponds to the conventional transimpedance type optical input section of FIG. 16 and is different from that of FIG. 5 in that a diode 2 and an operational amplifier 7 connected in parallel are used as a load of the photodiode 1. I used to. In the figure, 8 is an output resistance of the operational amplifier 7.

Here, the voltage amplification factor of the operational amplifier 7 is set to -A
_{Assuming v} (inverted output), the voltage V _OP applied to the output resistor 7 is as follows.

V _OP = V _o / (1 + 1 / A _v ) = (nkT / e) ln {(I _F / SA ^* T ² ) EXP (eφ _B / kT) +1} / (1 + 1 / A _v ) ... ( 11) From the equation (11), when A _v is sufficiently large, the voltage V _OP is
It becomes the same as the junction potential difference V _{F in the} equation (2), and the output characteristic of the optical input section of this embodiment is almost equal to that of the optical input section of FIG. This means that the transimpedance characteristic is automatically variable gain.

That is, the operational amplifier 7 of this embodiment functions as an automatic variable gain transimpedance amplifier, and since the input impedance is extremely low in the circuit, it has ideal load characteristics for the photodiode 1.

Therefore, the optical input section of this embodiment is the same as that shown in FIG.
In addition to having the same advantages as the conventional transimpedance type optical input unit of No. 6, there is a feature that the receiving dynamic range can be increased without using the AGC circuit.

FIG. 8 shows a circuit configuration of an optical input section of an optical receiving apparatus according to another embodiment of the present invention. It should be noted that the same reference numerals as those in FIG. 1 are given to the portions corresponding to the light input portion of FIG. 1, and detailed description thereof will be omitted.

In the figure, 9 is a path resistance connected in parallel with the diode 2 (SBD), which is a resistance for eliminating the output in the zero input state or the stray light input state and suppressing the self-bias effect at the pulse falling edge. Is.

The output current I _P flowing through the load of the optical input section thus constructed is expressed by the following equation, where the resistance value of the path resistor 9 is R _P.

I _P = SA ^* T ² EXP (−eφ _B / kT) · {EXP (eV _o / nkT) −1} + V _o / R _P (12) The equation (12) is a transcendental equation and is therefore analyzed. FIG. 9 shows a result (optical input power-output voltage characteristic) using the SBD described in the optical input section of FIG. From this figure, it can be seen that on the low optical input power side, the path resistance 7 controls the optical input power / output voltage characteristic, while on the high optical input power side, the SBD controls the optical input power / output voltage characteristic. .

Further, it is found that the optical input power (nonlinear threshold value) in which the relationship between the output voltage and the optical input power changes from linear to non-linear varies depending on the resistance value R _P of the path resistor 9, and the optical signal used You can adjust this value according to the input level of.

As an example, FIG. 10 shows the time response characteristic when R _P = 100 kΩ. It can be seen from FIG. 9 that the non-linear threshold value in this case is around 10 μW.
From 0, it can be seen that the output voltage obviously changes when the optical input power is 10 μW above and below.

That is, when the optical input power is up to 10 μW, the input / output characteristic is linear, and an output voltage proportional to the optical input power can be obtained, but at an optical input power higher than that, the same output voltage as in the case of FIG. 1 is obtained. Becomes

At this time, the optical input power is changed from 1 μW to 10
When it is in the range of μW, the signal for determining “1” or “0” tends to take an uncertain value, but since the output of the transmitting side is a digital output and the optical transmission distance is relatively short, the transmission level, Considering that the reception level can be easily set, there will be no problem if the transmission side transmits a signal having a level that does not become an uncertain value and the minimum input level is defined with certainty.

Further, according to this embodiment, the reference voltage is 0.
By setting 4V and the optical input power to 10 μW or more,
Operation of 500 Mbps or more is possible, and in this setting, since there is no quiescent output and self-biasing effect as shown in FIG. 6, noise resistance, that is, a level margin against noise can be significantly improved. .

Further, when the optical input power is 50 μW or more, the resistance value R _P of the path resistor 9 is set to 20 kΩ, or SBD is set.
By making the junction area of 5 μmφ or less, it is possible to operate up to a region considerably faster than 1 Gbps.

Thus, according to the present embodiment, the load of the light receiving element for converting the optical signal 3 into the electric signal is obtained by connecting the diode 2 having the forward polarity and the path resistor 7 in parallel, thereby increasing the noise and operating point. An optical input unit capable of suppressing the self-bias of

FIG. 11 is a diagram showing a circuit configuration of an optical input section of an optical receiving apparatus according to another embodiment of the present invention.

In the figure, 32 is a constant current source for outputting an output current I _C which is approximately the same as the output current I _P due to the optical input power, and 31
Is a level shift diode array for biasing the photodiode 1, and the level shift diode array 31 may be composed of an SBD. Also, 3
Reference numeral 4 represents an FET active layer, and 35 represents an FET buffer layer.

In this optical input section, when the optical signal 3 is not input, an output voltage which is obtained by substituting I _C in place of I _{F in} the equation (2) appears, and when the optical signal 1 is input,
The output voltage appears by substituting I _C −I _P instead of I _{F in} the equation (2).

That is, the output is obtained by the reverse logic with respect to the input of the optical signal 3, and has the following features. The first feature is
Since the dark current component of the photodiode is much smaller than the output current I _C of the constant current source 32, it hardly affects the output voltage and there is no quiescent drift due to temperature fluctuation.
The feature is that the output level is clamped to the “H” side by voltage and noise current etc. is hard to appear in the value at the time of zero input, so the threshold voltage can be set to “H” (large current) side, That is, noise and high-speed operability are enhanced.

FIG. 12 shows the constant current source 3 of the optical input section of FIG.
2 shows a circuit configuration that embodies No. 2.

The constant current source 32 is composed of a constant bias FET 33 in which the drain and the gate are short-circuited, and the drain is connected to the power supply potential V _{B. As} the FET 33, the channel width is narrowed by the normally-off type to reduce the saturation current level. An output current I _P that is as small as possible is used.

FIG. 13 shows the operating characteristics (time-output voltage) of the optical input section of FIG. 12 when the optical input power P _IN is 1 μW and the output current I _C is 1 μA. The output voltage level is S
It is possible to increase the size by increasing the number of BDs, and it is also possible to combine the other optical input units described above.

Note that this embodiment can be integrated as in the previous embodiments. For example, as shown in FIG. 14A, first, a high-resistance or anti-conductive semiconductor substrate 11a
Then, an n-type InP buffer layer 12, a GaInAs light absorption layer 13, and an n-type InP window layer 14 are formed on the substrate, and the entire surface is etched to form a photodiode in the semiconductor substrate 11a. In this way, the FET (constant current source) 32, the SBD (diode) 2, and the SBD (level shift diode) 31 may be formed on the exposed substrate surface. At this time, the FET 32 is set to MES (Metal
The semiconductor type allows the Schottky electrode 17 and the gate electrode to be formed at the same time.

The present invention is not limited to the above embodiment. For example, the same effect can be obtained by changing the material system or structure of the element of the above-mentioned embodiment. In addition, various modifications can be made without departing from the scope of the present invention.

[0104]

As described above in detail, according to the present invention, by using the diode of the forward polarity as the load element of the light receiving element for converting the optical signal into the electric signal, the ratio of the analog operation portion can be reduced, An optical receiving device that operates at high speed and has a simple structure can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing a circuit configuration of an optical input unit of an optical receiver according to an embodiment of the present invention.

FIG. 2 is a characteristic diagram showing a relationship between optical input power and output voltage.

FIG. 3 is a characteristic diagram showing a relationship between temperature and output voltage.

FIG. 4 is a diagram showing a specific element structure of the light input unit of FIG.

FIG. 5 is a diagram showing a circuit configuration of an optical input unit that can directly perform digital optical reception.

FIG. 6 is a characteristic diagram showing a relationship between time and output voltage.

FIG. 7 is a diagram showing a circuit configuration of an optical input unit of an optical receiving device according to another embodiment of the present invention.

FIG. 8 is a diagram showing a circuit configuration of an optical input unit of an optical receiving device according to another embodiment of the present invention.

FIG. 9 is a characteristic diagram showing a relationship between optical input power and output voltage.

FIG. 10 is a characteristic diagram showing a relationship between time and output voltage.

FIG. 11 is a diagram showing a circuit configuration of an optical input unit of an optical receiving device according to another embodiment of the present invention.

FIG. 12 is a diagram showing a circuit configuration that embodies a constant current source of the light input unit of FIG. 11.

FIG. 13 is a characteristic diagram showing the relationship between time and output voltage.

FIG. 14 is a diagram for explaining integration of an optical input unit.

FIG. 15 is a diagram showing a circuit configuration of a conventional optical receiver.

FIG. 16 is a diagram showing a circuit configuration of a conventional optical receiver.

[Explanation of symbols]

1 ... photodiode, 2 ... diode, 3 ... optical signal,
4 ... Output terminal, 5 ... Reference voltage source, 6 ... Comparator, 7 ... Operational amplifier, 8 ... Output resistance, 9 ... Path resistance, 11 ... N-type In
P semiconductor substrate, 12 ... n-type InP buffer layer, 13 ...
GaInAs light absorption layer, 14 ... N-type InP window layer, 15 ... Passivation dielectric film, 16 ... Zn diffusion region, 17 ... Schottky electrode, 18 ... Output electrode, 19 ...
Low-reflection coating film, 20 ... N-type ohmic electrode, 31 ... Level shift diode array, 32 ... Constant current source, 33 ...
FET, 34 ... FET active layer, 35 ... FET buffer layer.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H04B 10/04 10/06 8220-5K H04B 9/00 Y

Claims (4)

[Claims] 1. A light receiving element for converting an optical signal into an electric signal, and a diode connected to an output side of the light receiving element so as to be in a forward direction with respect to an electric signal output from the light receiving element, An optical receiver comprising: a diode and an output terminal provided between the light receiving element. 2. A light-receiving element for converting an optical signal into an electric signal, and a resistance element, which are connected in parallel with each other and are arranged in a forward direction with respect to an electric signal output from the light-receiving element. An optical receiver comprising a diode connected to an output side and an output terminal provided between the diode and the light receiving element. 3. A light receiving element for converting an optical signal into an electric signal, and a diode connected to the output side of the light receiving element so as to be in the forward direction with respect to the electric signal output from the light receiving element, An output terminal provided between the diode and the light receiving element, a comparator to which a voltage at the output terminal and a reference voltage are applied, and which outputs an electric signal of high voltage or low voltage according to the difference between these voltages, An optical receiving device comprising: 4. The diode according to claim 1, wherein the diode is a Schottky barrier type diode.
The optical receiver according to any one of 1.