JP2791550B2 - Optical receiving circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical receiving circuit for receiving high-speed modulated light and outputting the light-receiving signal, and to a technique for simultaneously outputting the light-receiving signal to two systems.

[0002]

2. Description of the Related Art For example, when performing error measurement on a high-speed digitally modulated optical signal, it is necessary to check the correlation between the intensity of input light and the error rate.

For this reason, conventionally, as shown in FIG. 7, an optical fiber 1 for transmitting a light to be measured is connected to an optical receiving circuit 2, and a light receiving signal of a photodiode 2a thereof is output to an error measuring device 3 for error measurement. A method in which the optical fiber 1 is replaced from the optical receiving circuit 2 to the optical power meter 4 and the intensity is measured with the light receiving signal of the photodiode 4a,
As shown in FIG. 8, light output from the optical fiber 1 is branched by an optical coupler 5, one of which is input to an optical receiving circuit 3, and the other is input to an optical power meter 4, and the error rate and the intensity are measured. The method of measuring at the same time was taken.

[0004]

However, as described above, in the method of measuring by replacing the optical fiber 1, there is a problem that the connection state of the optical fiber 1 varies and accurate measurement cannot be performed.

In the method of splitting the light from the optical fiber 1 by the optical coupler 5, the light receiving circuit 2 and the optical power meter 5 are used.
The intensity of the light input to the
There is a problem in that the S / N ratio becomes small and that measurement of light with low intensity cannot be performed accurately. In addition, both methods require two sets of optical receiving circuits, and there is a problem that the measurement system as a whole becomes expensive.

In order to solve this problem, a method of amplifying a light receiving signal of one photodiode and branching the amplified output to two systems is conceivable. In this method, a high-speed signal corresponding to a high-speed digital modulation signal is considered. An extremely expensive amplifier circuit having responsiveness and a wide dynamic range capable of measuring power in a wide input range is required.

[0007] The present invention solves this problem, and has a wide dynamic range and a wide dynamic range while having a configuration using one photodiode, and is an inexpensive optical receiving circuit capable of simultaneously outputting the received light signals to two systems. It is intended to provide.

[0008]

In order to achieve the above object, an optical receiving circuit according to the present invention comprises a first and second negative feedback differential type which outputs a voltage proportional to a current flowing through an inverting input terminal. An anode is directly connected to the DC amplifier circuit (22, 26) and the inverting input terminal of one of the first and second DC amplifier circuits in a DC manner, and the anode is connected to the inverting input terminal of the other DC amplifier circuit. A photodiode (21) having a cathode directly connected to direct current and flowing a light-receiving current corresponding to input light from the cathode side to the anode side; and the first (21) so that the cathode potential of the photodiode becomes higher than the anode potential. And a bias power supply circuit (24, 30) for applying a bias voltage to a non-inverting input terminal of at least one of the DC amplification circuits of the second DC amplification circuit.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows an optical receiving circuit 20 according to one embodiment.

The optical receiving circuit 20 receives a high-speed digitally modulated optical signal through the optical fiber 1 and converts it into an electric signal so that the error measurement and the intensity measurement can be performed simultaneously. And an intensity signal, and has a function of indicating the intensity.

That is, the light input from the optical fiber 1 is input to the photodiode 21 via the fiber connector 20a and a not-shown condensing optical system.
The photodiode 21 is constituted by a PIN photodiode or an avalanche photodiode having a high response speed, and causes a light-receiving current corresponding to an input optical signal to flow from the cathode K to the anode A.

The cathode K of the photodiode 21 is directly connected to an input terminal 22a of a first broadband DC amplifier circuit 22 for amplifying a light receiving current I flowing through the photodiode 21.

The first DC amplifier circuit 22 is composed of a current source type transimpedance amplifier having one input terminal 22a and one output terminal 22b. Inside the transimpedance amplifying element, the input terminal 22a side has an inverting input, and the inverting input side has a feedback resistor R
f and a bias power supply circuit 24 for applying a constant positive bias voltage Va to the non-inverting input side thereof.
And outputs a voltage proportional to the current flowing out from the output terminal 22b to the output terminal 22b.

It is known that the voltage on the inverting input side of such a negative feedback differential amplifier circuit 23 has the same potential as the voltage applied to the non-inverting input side. Therefore, this first
The voltage at the input terminal 22a of the DC amplifier circuit 22 becomes equal to the voltage Va of the internal bias power supply circuit 24. In addition,
Here, when the power supply voltage of the first DC amplifier 22 is 5 V, a bias voltage of about +1 V is applied to the input terminal 22a.

On the other hand, the anode A of the photodiode 21
Is connected to a second DC amplification circuit 26 via a filter circuit 25.
Are connected to the inverting input terminal 26a. The filter circuit 25 is a multi-stage (or single-stage) capacitor input type low-pass filter including a capacitor C and a coil L. The filter circuit 25 converts the DC component of the light-receiving current of the photodiode 21 into a second DC amplifier circuit. 26.

The second DC amplifying circuit 26 includes an operational amplifying element 27 and a plurality (two in FIG. 2) of feedback resistors 28a each having one end connected to an inverting input terminal 27a of the operational amplifying element 27.
, And range changeover switches 29a, 29b for selectively connecting between the other end of the plurality of feedback resistors 28a, 28b,... And the output terminal 27c of the operational amplifier 27 to form a negative feedback differential type. The output terminal 27c amplifies and outputs a voltage proportional to the current flowing into the inverting input terminal 27a of the operational amplifier 27. The operational amplifier element 27 is supplied with positive and negative power supplies (not shown).

The non-inverting input terminal 27b of the operational amplifier 27
From the bias power supply circuit 30 to the negative bias voltage Vb
Is given. Therefore, the second DC amplification circuit 26
Input terminal (inverting input terminal 27a) is connected to the bias voltage V
It has the same potential as b.

The bias power supply circuit 30 generates the voltage Vb from the negative power supply supplied to the operational amplifier 27.

Therefore, the cathode K of the photodiode 21 is connected to the input terminal 22a of the first DC amplification circuit 22.
A positive voltage Va is applied from the side, and a second voltage is applied to the anode A.
The negative voltage Vb is applied from the inverting input terminal 27a side of the operational amplifying element 27 of the DC amplifying circuit 26, and the photodiode 21 is reverse-biased by the voltage (Va-Vb).

The reverse bias causes the depletion interlayer capacitance in the photodiode 21 to become very small, so that the photodiode 21 can flow a light-receiving current corresponding to extremely high-speed digital modulation light.

The light receiving current I of the photodiode 21 is voltage-converted and amplified by the first DC amplifier circuit 22, and is input to an error measuring device 35 together with a clock signal extracted from the amplified signal by a clock extracting circuit 34 to measure an error. Receive.

On the other hand, the light receiving current I of the photodiode 21
Is amplified by the second DC amplification circuit 26, and the amplified signal is input to the voltmeter 33 together with the output of the bias power supply circuit 30. The voltmeter 33 indicates the magnitude of the optical power corresponding to the level of the amplified signal with respect to the bias voltage Vb. The voltmeter 33 operates the switch 29 so that the level of the amplified signal falls within the indicated range.
a, 29b switching control is performed.

The photodiode 2 of the light receiving circuit 20
The method of applying the reverse bias to the first DC-amplifier circuit is performed by connecting the non-inverting input terminals of the first and second DC amplifier circuits 22 and 26 in which the inverting input terminals are directly connected to the anode A and the cathode K of the photodiode 21 in a DC manner. Is applied by the bias voltage applied to the photodiode 21. As shown in FIG. is there.

That is, in the circuit shown in FIG. 2, the reverse bias voltage of the photodiode 21 becomes small due to the voltage drop caused by the light receiving current I of the photodiode flowing through the load resistor R. Although the response characteristics are deteriorated, the optical receiving circuit 20 utilizes the fact that the potential of the inverting input terminal of the negative feedback differential type DC amplifier circuit becomes the same as the potential applied to the inverted input terminal side. Since the reverse bias is applied to the photodiode without passing through the load resistor, the wideband response characteristics of the photodiode itself can be effectively used without being affected by the intensity fluctuation of the input light. In addition, since a reverse bias voltage is applied to both ends of the photodiode at the input operating point voltage of each DC amplifier circuit, even if the input terminal of each amplifier circuit and the photodiode are directly connected in a direct current manner, the amplifier circuit itself is not connected. Has no effect on operation. Therefore, there is no need to cut off the DC component by the capacitors Ca and Ck as shown in FIG. 2, and amplification from DC is possible.

In the light receiving circuit 20, the cathode K of the photodiode 21 is connected to the first DC amplification circuit 22 using a current-sinking transimpedance amplification element.
And the anode A is connected to the second DC amplifier 26 by the operational amplifier 27 to apply a reverse bias voltage to the photodiode 21.
And the first DC amplifier 22 is a current-sinking transimpedance amplifier, and a positive voltage higher than the bias power supply voltage in the transimpedance amplifier is applied to the bias power supply circuit 30.
Then, the reverse bias voltage may be applied to the photodiode 21 by applying the voltage to the non-inverting input terminal of the operational amplifier element 27 of the second DC amplifier circuit 26.

[0026]

[Other Embodiments] In the above-described embodiment, a transimpedance amplifier element having a built-in bias power supply and capable of obtaining a high-speed response characteristic is used as the first DC amplifier circuit. As described above, the first DC amplifier circuit 22 ′ may be composed of the operational amplifier 27 and the feedback resistor 28, as in the case of the second DC amplifier circuit 26. In this case, as shown in FIG. 3, the first DC amplifier circuit 22 '
If the non-inverting input terminal 27b of the operational amplifier element 27 on the side of the DC power supply circuit is grounded, the bias power supply circuit 3 on the side of the second DC amplifier circuit 26
Only the voltage Vb of 0 is applied to the photodiode 21 as a reverse bias voltage.

Further, a positive bias voltage may be applied to the non-inverting input terminal 27b of the operational amplifier element 27 on the first DC amplifier circuit 22 'side. In this case, the second DC amplifier circuit 26 side May be grounded.

As described above, the first and second DC amplifier circuits are composed of operational amplifier elements, and one of them outputs a high-speed digital modulation signal and the other outputs an intensity signal, as in the above embodiment. In this case, an operational amplifying element that provides high-speed response may be used on one side, and the DC amplifier circuit on the other side may be connected to the photodiode 21 via the filter circuit 25.

In the case where only the modulated component of the high-speed modulated light is simultaneously output to two systems, a current sink type is used as the second DC amplifier circuit 26 'as in the optical receiving circuit 50 shown in FIG. May be used by supplying power so that the voltage of its input terminal becomes negative.

As shown in FIG. 5, it is also possible to control the multiplication factor of an avalanche photodiode (hereinafter referred to as APD) by using one of the two systems of received light signal outputs, thereby expanding the dimic range.

That is, as shown in FIG. 6, the APD 21 'has such a characteristic that the ratio (multiplication factor) of the received light current to the input light increases as the reverse bias voltage increases.

The optical receiving circuit 60 shown in FIG. 5 utilizes this characteristic positively, and the bias receiving circuit 30 of the second DC amplifying circuit 26 is connected to a constant voltage circuit 31 for outputting a negative reference voltage Vr. And a comparator 32 that compares the output voltage Ve of the operational amplifier 27 with the reference voltage Vr and inputs the comparison signal to a non-inverting input terminal 27b of the operational amplifier 27. The output voltage Ve of the operational amplifier 27 is The reverse bias voltage for the APD 21 'is controlled so as to be always equal to the reference voltage Vr. It is desirable that the reverse bias voltage be varied by this control within a range where the high-frequency response of the ADP 21 'is not reduced.

By performing such control, when the intensity of the input light is small, the multiplication factor of the APD 21 'is increased, and when the intensity of the input light is large, the APD 21' is increased.
The multiplication factor of 1 'is reduced, and the dynamic range of the APD with respect to the input light can be greatly expanded.

[0034]

As described above, the optical receiving circuit according to the present invention provides one of the first and second negative feedback differential type DC amplifiers for outputting a voltage proportional to the current flowing to the inverting input terminal. The anode of the photodiode is directly connected to the inverting input terminal of the DC amplifier circuit in a DC manner, and the cathode of the photodiode is directly connected to the inverting input terminal of the other DC amplifier circuit in the DC manner. A bias voltage is applied to the inverting input terminal from a bias power supply circuit, the voltage of the inverting input terminal of the DC amplifier circuit is set to the same potential as the bias voltage, and the cathode voltage of the photodiode is set higher than the anode voltage.

For this reason, with a low-cost configuration, the input light is received over a wide band with a small loss and a wide dynamic range.
The light receiving signal can be output to two systems simultaneously. Therefore, it is possible to accurately and efficiently measure two optical signals that require simultaneous measurement and different signal processing methods, such as error measurement and intensity measurement.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention.

FIG. 2 is a circuit diagram for applying a reverse bias to a photodiode via a load resistor.

FIG. 3 is a circuit diagram of another embodiment of the present invention.

FIG. 4 is a circuit diagram of another embodiment of the present invention.

FIG. 5 is a circuit diagram of another embodiment of the present invention.

FIG. 6 is a diagram showing a change characteristic of a reverse bias voltage versus a multiplication factor of an avalanche photodiode.

FIG. 7 is a diagram showing a measurement system using a conventional optical receiving circuit.

FIG. 8 is a diagram showing a measurement system using a conventional optical receiving circuit.

[Explanation of symbols]

 REFERENCE SIGNS LIST 20 light receiving circuit 21 photodiode 22 first DC amplifier circuit 24 bias power circuit 25 filter circuit 26 second DC amplifier circuit 27 operational amplifier element 30 bias power circuit 33 voltmeter

──────────────────────────────────────────────────の Continued on front page (51) Int.Cl. ⁶ Identification code FI H04B 10/06 10/14 10/26 10/28

Claims (1)

(57) [Claims] 1. A negative feedback differential type first and second DC amplifier circuit (22, 26) for outputting a voltage proportional to a current flowing through an inverting input terminal; and the first and second DC amplifier circuits. The anode is directly connected to the inverting input terminal of one of the DC amplifying circuits, and the cathode is directly connected to the inverting input terminal of the other DC amplifying circuit. And a non-inverting input terminal of at least one of the first and second DC amplification circuits so that the cathode potential of the photodiode is higher than the anode potential. And a bias power supply circuit (24, 30) for applying a bias voltage.