JP2006304249A - Optical receiver and measuring method of incident light signal strength - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical receiver which can monitor an optical signal with high precision. <P>SOLUTION: The optical receiver 1a is equipped with a photodiode 2, which generates a photocurrent I<SB>org</SB>which corresponds to input light O<SB>in</SB>; a current mirror portion 6 which generates a monitor current I<SB>mon</SB>which corresponds to the photocurrent I<SB>org</SB>, a current voltage converter 10 which converts the monitor current I<SB>mon</SB>into a voltage signal V<SB>RXP</SB>; a current path switch S<SB>1</SB>which connects and cuts a current path of the monitor current I<SB>mon</SB>; a switch controller 15 which sends a control signal SEL to the current path switch S<SB>1</SB>; and a difference signal generating portion 16 which receives a first voltage signal V<SB>RXP</SB>(1) which is changed by the current voltage converter 10 at the connection of the current path and a second voltage signal V<SB>RXP</SB>(0), which is changed by the current voltage converter 10 at cutting of the current path, and generates excess of the first voltage signal V<SB>RXP</SB>(1) and the second voltage signal V<SB>RXP</SB>(0) as a monitor signal V<SB>D</SB>of the input light. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical receiver that receives an optical signal in optical communication, and a method for measuring an incident optical signal intensity using the optical receiver.

As a circuit for monitoring the input level of an optical signal in an optical receiver, a circuit described in Patent Document 1 below is known. In this circuit, by adding a diode between the output of the operational amplifier and the output of the feedback loop in the voltage follower circuit, the output voltage of the operational amplifier is shifted to the positive side, and errors due to the operational amplifier output voltage range are reduced. is doing.
JP 2003-198279 A

  The conventional monitor circuit operates by supplying a power supply voltage of 0 to Vcc to the operational amplifier. When the intensity of the optical signal input to the optical receiver is weak and sufficient current is not generated in the light receiving element, the potential difference generated in the resistance element of the current-voltage conversion circuit in the monitoring circuit, that is, I The xR product will approach 0V as much as possible. Therefore, the operating point of the operational amplifier approaches as much as 0 V, and deviates from the linear operational range of the operational amplifier.

  In the circuit described in Patent Document 1, by adding a diode to the output side of the operational amplifier, the output of the operational amplifier is shifted to the positive side by the forward voltage of the diode even when the output of the feedback loop approaches 0V. Therefore, the output side of the operational amplifier can be kept within the linear operating range, and the limit of Rail to Rail output characteristics can be avoided. However, it is impossible to avoid an error between the input voltage and the output voltage caused by the input offset generated on the input side of the operational amplifier. As a result, it is difficult to accurately monitor the optical signal when the intensity of the optical signal is weak.

  Therefore, the present invention has been made in view of such a problem, and an object thereof is to provide an optical receiver capable of accurately monitoring an optical signal and a method for measuring an incident optical signal intensity.

  In order to solve the above problems, a first optical receiver of the present invention includes a photodiode that generates a photocurrent corresponding to input light, and a monitor that detects the photocurrent and generates a monitor current corresponding to the photocurrent. Connecting a current generation circuit, a current-voltage converter that receives a monitor current and converts a current signal representing the monitor current into a voltage signal, and a current signal current path between the monitor current generation circuit and the current-voltage converter And a current path switch to be disconnected, a switching control unit that sends a control signal for connecting and disconnecting the current path to the current path switch, and a first voltage signal converted by the current-voltage converter when the current flow path is connected, The second voltage signal converted by the current-voltage converter at the time of cutting the current flow path is received according to the control signal, and the monitor for the input light is based on the difference between the first voltage signal and the second voltage signal Generate signal Characterized in that it comprises a that the difference signal generating unit.

  The second optical receiver of the present invention includes a photodiode that generates a photocurrent corresponding to input light, a monitor current generation circuit that detects the photocurrent and generates a monitor current proportional to the photocurrent, A current-voltage converter that receives the monitor current and converts the monitor current into a voltage signal, a current path switch interposed in a current path between the monitor current generation circuit and the current-voltage converter, and a control signal as a current path The switching control unit to be sent to the switch, the first voltage signal converted by the current-voltage converter when the current path is connected, and the second voltage signal converted by the current-voltage converter when the current path is disconnected are used as control signals. And a difference signal generation unit configured to generate a monitor signal related to input light based on a difference between the first voltage signal and the second voltage signal.

  In these optical receivers, a photocurrent generated in response to input light in a photodiode is monitored as a monitor current, and a monitor current (a current signal representing) is converted into a voltage signal by a current-voltage converter. . At this time, the first voltage signal depending on the monitor current (corresponding voltage signal) and the offset voltage and a signal portion depending on the offset voltage of the first voltage signal are obtained by the current-voltage converter. Two voltage signals are generated separately, and an input light monitor signal is generated based on the difference between the two voltage signals. Therefore, by canceling the influence of the input offset included in the monitor signal, the accuracy of the monitor signal can be improved even when the intensity of the optical signal is weak and the photocurrent is small.

  It is also preferable to further include an offset voltage generation circuit that is connected to the current-voltage converter and generates a predetermined offset voltage in the output voltage signal. By adopting such a configuration, the voltage signal generated by the current-voltage converter corresponding to the intensity range of the input light can be kept within a predetermined voltage range. As a result, the calculation in the subsequent difference signal generation unit can be facilitated.

  The third optical receiver of the present invention includes a photodiode that generates a photocurrent corresponding to input light, a monitor current generation circuit that detects a photocurrent and generates a monitor current corresponding to the photocurrent, And an operational amplifier having a first input terminal connected to the monitor current generation circuit, a second input terminal for inputting a reference voltage, and an output terminal connected to the first input terminal via a feedback resistor. A current-voltage converter that converts the monitor current into a voltage signal; and a difference signal generator that generates a monitor signal related to input light based on a difference between a voltage value at the first input terminal of the operational amplifier and a voltage signal from the output terminal; It is characterized by providing.

In such an optical receiver, a photocurrent generated in response to input light (incident light signal) in a photodiode is monitored as a monitor current, and the monitor current is converted into a voltage signal by a current-voltage converter. . At this time, in the current-voltage converter, most of the monitor current flows through the feedback resistor and is converted into a voltage signal. Further, in the operational amplifier, the first input terminal and the second input terminal are virtually short-circuited (virtual short), but the input offset voltage is the difference between the first input terminal and the second input terminal. Occur between. That is, with respect to the reference voltage V at the second input terminal, the voltage value at the first input terminal is a value V ± V _ofs including the input offset voltage value V _ofs . From this, the difference signal generation unit generates a monitor signal related to the input light based on the difference between the voltage value V ± V _ofs at the first input terminal and the voltage signal from the output terminal, so that the monitor signal includes Even if the influence of the included input offset voltage is canceled and the intensity of the incident optical signal is weak and the photocurrent is small, the accuracy of the monitor signal can be improved.

  Further, a signal switch that selectively provides one of the voltage value at the first input terminal and the voltage signal from the output terminal to the difference signal generation unit, and one of the voltage value and the voltage signal is selected. And a switching control unit that sends a control signal to the signal switch. The difference signal generation unit preferably receives the voltage value and the voltage signal according to the control signal. Thereby, in the difference signal generation unit, a circuit for receiving each of the voltage value at the first input terminal and the voltage signal from the output terminal can be shared, so that the circuit scale of the difference signal generation unit can be reduced. Further, when the difference signal generation unit performs digitization processing, both the voltage value at the first input terminal and the voltage signal from the output terminal can be converted by a common analog-digital converter. It is also possible to cancel out the offset caused by.

  An amplifier configured to convert a photocurrent from a photodiode into a received signal and change a gain-frequency characteristic; and an amplifier control unit that sends an amplifier control signal for changing the gain-frequency characteristic to the amplifier; The amplifier control unit is connected to the first input terminal of the operational amplifier, and according to the magnitude of the reference voltage at the second input terminal that is in a virtual short-circuit relationship with the first input terminal. It is also preferable to generate an amplifier control signal. As described above, the amplifier that converts the photocurrent into the received signal is configured to be able to change the gain-frequency characteristic. For example, when the signal frequency of the received signal is relatively high, the gain is lowered to reduce the cutoff frequency. When the signal frequency of the received signal is relatively low, an appropriate gain-frequency characteristic can be selected according to the signal frequency of the received signal, such as increasing the gain and lowering the cutoff frequency. Further, in this optical receiver, the amplifier control unit is connected to the first input terminal of the operational amplifier, and according to the reference voltage at the second input terminal that is in a virtual short-circuit relationship with the first input terminal. An amplifier control signal is generated. As a result, the gain-frequency characteristic of the amplifier can be changed by changing the reference voltage input to the second input terminal. Therefore, it is necessary to provide a signal input terminal for changing the gain-frequency characteristic of the amplifier independently. The number of input terminals to the circuit can be reduced.

  Further, a package for accommodating a photodiode, a monitor current generation circuit, an amplifier, and an amplifier control unit is further provided, and the monitor current generation circuit, the amplifier control unit, and the first input terminal of the operational amplifier are connected via one terminal of the package. It is also preferable that they are connected to each other. As a result, among the terminals to be provided in the package, the monitor current output terminal and the terminal for inputting a signal to the amplifier control unit can be shared, so that the number of terminals required for the package can be reduced.

  Alternatively, the first incident light signal intensity measuring method of the present invention is a measuring method for measuring the intensity of the incident light signal, the step of generating a monitor current from the output signal of the photodiode, and the offset voltage generating circuit. A step of generating a reference current; and a step of detecting a reference current and a current obtained by adding the monitor current and the reference current, and generating a difference signal between the two in a difference signal generation unit. According to such a method for measuring the incident light signal intensity, when the incident light intensity is measured from the monitor current of the incident light, the difference between the reference current and the current obtained by combining the monitor current and the reference current is used. Therefore, it is possible to accurately measure the intensity of an optical signal having a wide dynamic range, particularly an optical signal having a low intensity.

  Alternatively, according to the second method of measuring the incident light signal intensity of the present invention, a feedback resistor is connected between the input terminal and the output terminal, and the step of generating the monitor current from the output signal of the photodiode receiving the incident light signal. A step of converting a monitor current into a voltage signal using the operational amplifier, and a step of generating a monitor signal corresponding to the intensity of the input optical signal based on the difference between the voltage value at the input end and the voltage signal from the output end And comprising. As described above, the voltage value at the input terminal includes the input offset voltage. Therefore, by generating a monitor signal corresponding to the intensity of the incident light signal based on the difference between the voltage value at the input end and the voltage signal from the output end, the influence of the input offset voltage included in the monitor signal is reduced. It is possible to accurately measure the intensity of an optical signal that is canceled out and has a wide dynamic range, in particular, an optical signal having a low intensity.

  According to the optical receiver and the incident optical signal intensity measuring method of the present invention, it is possible to monitor an optical signal with high accuracy.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of an optical receiver and a method for measuring an incident optical signal intensity according to the invention will be described in detail with reference to the drawings. In the description of the drawings, the same or corresponding parts are denoted by the same reference numerals, and redundant description is omitted.

(First embodiment)
FIG. 1 is a diagram showing a configuration of an optical receiver which is a preferred embodiment of the present invention. The optical receiver 1a shown in the figure is an optical communication module for outputting output signals S _{out +} and S _out− corresponding to an input signal light O _in to the outside, and a photocurrent corresponding to the signal light O _in. A photodiode 2 such as a PIN photodiode, an avalanche photodiode, and the like. A photoelectric conversion unit 5 having a filter circuit 3 that is connected to the electrodes and that temporally averages the photocurrent I _org generated in the photodiode 2 according to the intensity of the signal light O _in and outputs a current signal I _pd ; A monitor that detects the current signal I _pd output by the filter circuit 3 and is proportional to the current signal I _pd Current mirror unit for generating a current I _mon and (monitor current generating circuit) 6, a signal processing unit 7 that calculates the monitor signal of the intensity of the signal light O _in based on the monitor current I _mon output from the current mirror portion 6 And a limiting amplifier 8 which is connected to the output of the transimpedance amplifier 4 and amplifies the voltage signal from the transimpedance amplifier 4 and outputs the voltage signal as output signals S _{out +} and S _out− .

The photocurrent I _org generated by the photodiode 2 is converted into a voltage signal by the transimpedance amplifier 4 and output as a differential signal. The limiting amplifier 8 generates a differential signal of the differential signal. The difference signal is amplified to two output signals S _{out +} and S _out− whose signs are opposite to each other and output to a reception signal processing circuit (not shown) at the _subsequent stage. By taking _{out the} output signals S _{out +} and S _out− by differential processing in this way, the signal amplitude in the photocurrent I _org can be handled in an equivalently doubled manner. As a result of shortening the transition time, higher-speed signal processing is enabled.

The current I _pd flowing to the filter circuit 3 side of the current mirror unit 6 is proportional to the average intensity P _in [W] of the signal light O _in incident on the photodiode 2, for example, approximately I _pd = r × P _in (R represents a real number with r> 0). The current mirror unit 6 outputs a monitor current I _mon = I _pd / α to the signal processing unit 7 at a conversion factor of α times (α represents a real number where α> 0).

  Hereinafter, each component of the signal processing unit 7 will be described in detail.

The signal processing unit 7 includes a current path switch S ₁ , a current / voltage converter 10, an analog / digital converter (analog / digital conversion unit) 11 that converts a voltage signal into a digital signal, and a digital signal output from the analog / digital converter 11. A selector (selector unit) 12 to be sent to the (arithmetic unit) 13, a computing unit 13 that performs a predetermined computing process on the digital signal sent from the selector 12, and a register 14 that stores data output from the computing unit 13 together but are connected in this order, the switching control unit 15 for controlling the operation of the current path switch S ₁ and the selector 12 in the current path switches S ₁ and the selector 12 is connected, a predetermined current-voltage converter 10 offset voltage V offset voltage generating circuit 17 for generating _pofs is connected consists . The analog-digital converter 11, the selector 12, and the arithmetic unit 13 constitute a difference signal generation unit 16 that generates a monitor signal of the signal light O _in .

Current-to-voltage converter 10 is connected through a current path switch _{S 1} to the current mirror unit 6 receives the monitor current _{I mon} corresponding to the average intensity _{P in} of the signal light _{O in,} a voltage signal a current signal _{I mon} Convert to _VRXP . At this time, the current-voltage converter 10 outputs the generated voltage signal V _RXP to the analog-digital converter 11.

The current path switch S ₁ is a switch element that is connected (intervened) between the current mirror unit 6 and the current-voltage converter 10 and connects and disconnects the current path of the monitor current I _mon flowing from the current mirror unit 6. . Specifically, the current path switch S ₁ receives a state of high control signal SEL from the switching control section 15 level (logical value 1), the connection between the current mirror portion 6 and a current-voltage converter 10 Turn on. In contrast, the current path switch S ₁ receives a control signal SEL from the switching control unit 15 in a state of low level (logical value 0), the connection between the current mirror portion 6 and a current-voltage converter 10 Turn off.

The switching control unit 15 sends a control signal SEL for connecting and disconnecting the current path of the monitor current I _mon to the current flow path switch S ₁ and the selector 12. Specifically, the switching control unit 15 generates a high-level control signal SEL to connect the current path of the monitor current I _mon , while the low-level control signal MON generates a low level control signal MON to cut the current path of the monitor current I _mon . A control signal SEL is generated. Then, the switching control unit 15 generates a pulse signal in which a high level control signal SEL and a low level control signal are alternately arranged in time series, and sends the pulse signal to the current flow path switch S ₁ and the selector 12. To do.

The offset voltage generation circuit 17 is connected to the current / voltage converter 10, inputs the offset voltage ± V _pofs to the current / voltage converter 10, and outputs an intentional voltage signal _VRXP generated by the current / voltage converter 10. A typical offset voltage ± V _pofs is added.

The output of the current / voltage converter 10 is connected to an analog / digital converter 11, and the analog / digital converter 11 converts the voltage signal V _RXP output from the current / voltage converter 10 into a digital signal D _RXP having a digital value.

A selector 12 is connected to the output of the analog-digital converter 11. The selector 12, as well as receives the digital signal _{D RXP} from analog to digital converter 11, in synchronization with the output timing of the control signal SEL from the switching control unit 15, the digital signal _{D RXP} received from the analog digital converter 11 to the calculator 13 Output.

The arithmetic unit 13 outputs a first digital signal D _RXP (1) output from the selector 12 in synchronization with the control signal SEL = 1 and a second digital signal output in synchronization with the control signal SEL = 0. D _RXP (2) is received, and a difference digital value (difference signal) V _D is generated by calculating a difference between the two digital signals D _RXP (1) and D _RXP (2). Further, the arithmetic unit 13 stores the calculated difference digital value V _{D in} the register 14 as an intensity monitor value of the signal light O _{in in} the photodiode 2.

  Next, the circuit configuration of the signal processing unit 7 will be described in more detail.

Referring to FIG. 2, is connected resistive element 18 via the switch S ₂ is the connection point between the current mirror portion 6 and a current path switch S _1, the opposite side of the terminal and the switch S ₂ of the resistive element 18 Is connected to ground potential. Switch _{S 2} receives the control signal SEL and the opposite polarity of the signal SEL2 from the switching control unit 15 turns on the connection between the current mirror portion 6 and the resistance element 18 when the signal SEL2 = 1, the signal SEL2 = 0 In this case, the connection between the current mirror unit 6 and the resistance element 18 is turned off. With such a configuration, the path of the monitor current I _mon from the current mirror unit 6 can be switched to either the current-voltage converter 10 or the resistance element 18 in accordance with the level (logical value) of the control signal SEL. it can.

Current-to-voltage converter 10 consists of an operational amplifier 20 having a resistor 19 as a feedback resistor to the inverting input of the operational amplifier 20, the monitor current I _mon through the current path switch S ₁ is input, the non-inverting input, later The output terminal 26 of the reference voltage generating circuit 24 and the non-inverting input terminal of the analog / digital converter 11 are connected. In such a configuration, the transimpedance, which is the current-voltage conversion gain of the current-voltage converter 10, is determined by the resistance value R _mon of the resistance element 19. That is, the monitor current I _mon = I _pd / α is converted by the current-voltage converter 10 into a voltage R _mon × I _pd / α proportional to the monitor current. Further, an offset voltage generation circuit 17 that is a constant current source is connected to the inverting input of the operational amplifier 20. Constant current (reference _{current) I ofs} generated in the offset voltage generating circuit 17, by flowing into the resistor element 19, adds an offset voltage _{± V} pofs the output voltage _{V RXP} of the operational amplifier 20. An input offset voltage ± V _ofs generated inside the operational amplifier is generated between the two input terminals of the operational amplifier 20. Here, it is assumed that the operational amplifier 20 is an operational amplifier having an infinite input impedance including a MOS transistor on the input side in order to prevent an offset due to an input current.

The output of the operational amplifier 20 in the current-voltage converter 10 is connected to the inverting input terminal of the analog-digital converter 11, and the non-inverting input terminal of the operational amplifier 20 is connected to the non-inverting input terminal of the analog-digital converter 11. The analog-digital converter 11 is supplied with two reference potentials in the analog-digital conversion from the reference voltage generation circuit 24. Specifically, the analog-digital converter 11 is supplied with reference potentials V _REF1 and V _REF2 from output terminals 25 and 26 of the reference voltage generation circuit 24, respectively.

The selector 12 receives the first digital signal D _RXP (1) and the second digital signal D _RXP (0) from the analog-digital converter 11, separates these digital signals, and _{performs the subsequent} averaging circuit 21a. , 21b. Specifically, the analog-to-digital converter 11, the control signal and the digital signal _{D RXP} (0) when the SEL = 0, the control signal SEL = digital signal _{D RXP} (1) when the 1, but is time-divided The selector 12 separates the two time-divided digital signals D _RXP (0) and D _RXP (1) while receiving the control signal SEL. Then, the selector 12 outputs the first digital signal D _RXP (1) to the first averaging circuit 21a and the second digital signal D _RXP (0) to the second averaging circuit 21b.

Averaging circuit 21a, 21b, the digital signal _D RXP ₍₁₎ received from the selector _12, in order to remove the temporal fluctuation of the quantization noise and the low frequency from the _{D RXP} (0), the digital signal _D RXP (1) , D _RXP (0) is subjected to suppression processing using a moving average filter or IIR filter. At that time, the averaging circuits 21a and 21b perform an averaging process on the digital signals D _RXP (1) and D _RXP (0) for m samples (m is an integer of 1 or more) output from the selector 12. Execute. The averaging circuits 21a and 21b _store the digital signals D _RXP (1) and D _RXP (0) after the suppression processing in the registers 22a and 22b, respectively.

The arithmetic circuit 23 reads out the respective digital signals D _RXP (0) and D _RXP (1) stored in the registers 22a and 22b, and also calculates a difference digital value between the digital signals D _RXP (0) and D _RXP (1). V _D is calculated. Then, the arithmetic circuit stores the calculated difference digital value V _{D in} the register 14 as an intensity monitor value of the signal light O _in .

The reference voltage generation circuit 24 is a circuit that sets a reference potential set at a non-inverting input terminal of the operational amplifier 20 and two reference potentials in analog-digital conversion in the analog-digital converter 11. The reference voltage generating circuit 24 has three output terminals 25, 26, and 27. The output terminal 25 is set to a predetermined potential V _REF1 = ¼V _REF , and the output terminal 26 is set to a predetermined potential V _REF2 = _3/4 V _REF . The output terminal 27 is set to a predetermined potential V _REF . The value of the potential V _REF is appropriately set according to the range of the monitor current I _mon output from the current mirror unit 6 and the resistance value of the resistance element 19. The output terminal 25 of the reference voltage generation circuit 24 is an input terminal for setting one reference potential of the analog / digital converter 11, and the output terminal 26 is a non-inverting input terminal of the operational amplifier 20 and the other reference potential of the analog / digital converter 11. Each is connected to a setting input terminal.

Next, a method for calculating the intensity monitor value of the signal light O _{in in} the signal processing unit 7 will be described.

上記式（１）において、オフセット電圧発生回路１７によって生成されるオフセット電圧Ｖ_ｐｏｆｓ＝Ｒ_ｍｏｎ×Ｉ_ｏｆｓは、オペアンプ２０で発生する入力オフセット電圧±Ｖ_ｏｆｓが正電圧の場合に、アナログ−デジタル変換後の値が０以下になるのを防ぐために付加されるものである。 In the current-voltage converter 10, when the control signal SEL = 1, a current I _pd / α + I _{ofs obtained} by combining the current from the current mirror unit 6 and the constant current I _ofs generated by the offset voltage generation circuit 17 is _fed back. It is supplied to the resistance element 19. On the other hand, when the control signal SEL = 0, only the constant current I _ofs generated by the offset voltage generation circuit 17 is supplied to the feedback resistance element 19. Since the non-inverting input terminal of the operational amplifier 20 is set to the potential V _REF2 = 3 / 4V _REF , the voltage V _RXP− (SEL) input to the inverting input of the analog-digital converter 11 and the non-inverting input terminal of the analog-digital converter 11 are set. The voltage V _{RXP +} (SEL) input to the inverting input is given as a differential signal such as the following equations (1) and (2) according to the logic value of the control signal SEL.

In the above formula (1), the offset voltage _{V pofs = R mon} × _{I ofs} generated by the offset voltage generating circuit 17, when the input offset voltage ± _{V ofs} generated by the operational amplifier 20 is positive voltage, an analog - digital converter It is added to prevent the later value from becoming 0 or less.

The analog-digital converter 11 converts the input voltage difference V _RXP (SEL) = V _{RXP +} (SEL) −V _RXP− (SEL) into a digital value D _RXP (SEL). Here, the voltage signals V _RXP− (SEL) and V _{RXP +} (SEL) input to the analog-digital converter 11 are based on the reference potentials V _REF1 and V _REF2 , and the minimum value V _REF1 = 1/4 V _REF and the maximum value V _REF1. = 3 / 4V _REF . Therefore, the maximum value of V _RXP (SEL) = V _{RXP +} (SEL) −V _RXP− (SEL) is 1 / 2V _REF and the minimum value is −1 / 2V _REF . Therefore, when the resolution is N bits, the analog-digital converter 11 converts V _RXP (SEL) = 1 / 2V _REF into a code of digital value D _RXP (SEL) = “2 ^N−1 ” (decimal number). V _RXP (SEL) = 0 is converted into a code of digital value D _RXP (SEL) = “2 ^N−1 −1”, and V _RXP (SEL) = − 1 / 2V _REF is converted to digital value D _RXP (SEL ) = Operates to convert the code to “0”.

上記式中、伝達関数内の各値“Ｖ_ＲＸＰ−（１）”，“Ｖ_ＲＸＰ−（０）”，“Ｒ_ｍｏｎ×Ｉ_ｐｄ／α”は、平均化処理後の値を示す。 The digital values D _RXP (SEL) output from the analog-digital converter 11 are averaged by the averaging circuits 21a and 21b, respectively, and the difference digital values of the respective digital values D _RXP (1) and D _RXP (0). The value V _D is stored in the register 14 as the intensity monitor value of the signal light O _in . Here, assuming that the transfer function of the analog-digital converter 11 is f, the obtained differential digital value V _D is given by the following equation (3).

In the above equation, the values “V _RXP− (1)”, “V _RXP− (0)”, and “R _mon × I _pd / α” in the transfer function indicate values after the averaging process.

FIG. 3 shows a timing chart of each signal processed in the signal processing unit 7. In Fig. 3, (a) is a timing chart of the control signals SEL, (b), the output signal _{V RXP} timing chart of the operational amplifier 20, (c), the output signal _{D RXP} timing chart of the analog-to-digital converter 11, (D) is a timing chart of data stored in the register 22a, (e) is a timing chart of data stored in the register 22b, and (f) is a timing chart of data stored in the register 14. The data stored in the registers 22a and 22b is averaged using a moving average filter having a depth of 4 bits. Thereby, it can be seen that the influence of the quantization error is sufficiently suppressed in the generated monitor value V _D.

According to the optical receiver 1a as described above, the photocurrent Iorg generated corresponding to the input optical O _in the photo diode 2 is monitored as a monitor current I _mon, the monitor current by a current-voltage converter 10 I _mon Is converted into a voltage signal _VRXP . At this time, the current-voltage converter 10, the first and the voltage signal _{V RXP} (1) which depends on the voltage signal corresponding to the monitor current _{I mon} and the offset voltage _{V ofs,} the offset voltage of the first voltage signal a portion of the signal depends on V _ofs is a second voltage signal V _{RXP (0)} is separately generated, the monitor signal V _D of the input light O _in based on the difference of the two voltage signals are generated. Therefore, the intensity of the signal light O _in is weak because the influence of the input offset V _ofs generated by the operational amplifier and the analog-digital converter included in the monitor signal and the influence of the intentionally added offset are offset. Even when the photocurrent Iorg is small, the accuracy of the monitor signal can be improved. Furthermore, the input offset of the operational amplifier is affected by temperature fluctuations and power supply voltage. By subtracting this input offset from the monitor signal, the light intensity can be monitored stably against power supply voltage and temperature fluctuations. .

Moreover, the range of the output voltage in the current-voltage converter _10, 1 / 4V REF By setting the to 3 _{/ 4V REF,} limitation of the output voltage range of the single supply op amp (typically, the lower limit is 100 mV) also receive Absent.

4A is a graph showing the monitoring result of the intensity of signal light in a conventional optical receiver that does not have a current path switch, a switching control unit, and a difference signal generation unit, and FIG. 4B shows the present embodiment. It is a graph which shows the monitoring result of the intensity | strength of the signal light in. In the figure, the horizontal axis represents the average intensity P _in [dBm] of the signal light, and the vertical axis represents the logarithmic value of the monitor signal V _D. A range surrounded by a dotted line represents a range of error ± 2 dB. From these results, in the conventional optical receiver, the error of the monitor signal becomes large when the intensity of the signal light is small, and the monitor signal becomes zero or less when the input offset V _ofs is a positive voltage. Therefore, when analog-digital conversion is performed, the error is further increased. On the other hand, in the optical receiver 1a, the error is small in a wide range of the intensity of the signal light.

Moreover, it is preferable that the current-voltage converter 10 further includes an offset voltage generation circuit 17 that generates a predetermined offset voltage in the output voltage signal V _RXP (SEL). With such a configuration, the voltage signal V _RXP (SEL) generated by the current-voltage converter 10 can be within a predetermined voltage range corresponding to the intensity range of the input light O _in . As a result, analog-digital conversion in the subsequent difference signal generation unit 16 can be facilitated.

  Further, since the monitor of the optical input intensity is realized by the configuration of the analog-digital converter 11, the selector 12, and the arithmetic unit 13, it is possible to easily achieve downsizing and cost reduction of the optical receiver.

(Second Embodiment)
FIG. 5 is a diagram showing a configuration of an optical receiver which is another preferred embodiment of the present invention. The optical receiver 1b shown in FIG. 1 includes a photoelectric conversion unit 5 having a photodiode 2, a filter circuit 3, and a transimpedance amplifier 4, a current mirror unit (monitor current generation circuit) 6, a signal processing unit 28, a limiter. And a ting amplifier 8. Among these components, the configuration and operation other than the signal processing unit 28 are the same as those in the first embodiment, and a detailed description thereof will be omitted.

The signal processing unit 28 includes a current / voltage converter 31, a signal switch 36, an analog / digital converter 11, a selector 12, a calculator 13, and a register 14 connected in this order, and the signal switch 36 and the selector 12 connected to the signal switch 36. And the switching control part 33 which controls operation | movement of the selector 12 is connected and comprised. Analog-to-digital converter 11, a selector 12 and a calculator 13, constitutes a difference signal generator 16 for generating a monitor signal of the signal light _{O in.}

The current-voltage converter 31 is connected to the current mirror unit 6 and receives the monitor current I _mon corresponding to the average intensity P _in of the signal light O _in and converts the monitor current I _mon into the voltage signal V _RXP . The current-voltage converter 31 outputs the generated voltage signal V _RXP to the signal switch 36.

Specifically, the current-voltage converter 31 includes the operational amplifier 20. A resistance element 43 is connected as a feedback resistor between the inverting input terminal (first input terminal) 20 a and the output terminal 20 c of the operational amplifier 20. The inverting input terminal 20 a is connected to the current mirror unit 6, and most of the monitor current I _mon flows through the resistance element 43 to the output terminal 20 c side. Further, the non-inverting input terminal (second input terminal) 20b of the operational amplifier 20 is connected to the output terminal 26 of the reference voltage generation circuit 24, and the reference voltage V _REF3 (for example, 3 / 4V _REF ) is supplied from the reference voltage generation circuit 24. ) The non-inverting input terminal 20 b is also connected to the non-inverting input terminal of the analog / digital converter 11. The inverting input terminal 20 a and the non-inverting input terminal 20 b are in a virtual short-circuit relationship with each other by the internal circuit of the operational amplifier 20. However, in practice, an input offset voltage ± V _ofs generated inside the operational amplifier is generated between the inverting input terminal 20a and the non-inverting input terminal 20b of the operational amplifier 20. Therefore, the voltage value _{V in} at the inverting input terminal 20a is substantially equal to the reference voltage _{V REF3} and the sum of the input offset voltage ± _{V ofs.} In the present embodiment, the resistance element 43 is configured such that its resistance value can be changed, and the resistance value of the resistance element 43 is set by, for example, a switching control unit 33 described later.

The signal switch 36 is connected between the inverting input terminal 20 a and the output terminal 20 c of the current-voltage converter 31 and the analog-digital converter 11. The signal switch 36 is a switch element that selectively provides one of the voltage value V _in at the inverting input terminal 20 a and the voltage signal V _RXP from the output terminal 20 c to the difference signal generation unit 16. Specifically, when the signal switch 36 receives the control signal SEL3 from the switching control unit 33 in a high level (logical value 1) state, the signal switch 36 connects the output terminal 20c and the analog-digital converter 11. On the other hand, when the signal switch 36 receives the control signal SEL3 from the switching control unit 33 in a low level (logical value 0) state, the signal switch 36 connects the inverting input terminal 20a and the analog-digital converter 11.

Switching control unit 33, a control signal SEL3 for selecting either one of the voltage value _{V in} and the voltage signal _{V RXP,} and sends the signal switch 36 and the selector 12. Specifically, the switching control unit 33 to select the voltage signal V _RXP, while generating a control signal SEL3 of high level, to select the voltage value V _in, generates a control signal SEL3 at a low level . Then, the switching control unit 33 generates a pulse signal in which the high-level control signal SEL3 and the low-level control signal SEL3 are alternately arranged in time series, and sends the pulse signal to the signal switch 36 and the selector 12.

The output of the signal switch 36 is connected to the analog-digital converter 11, and the analog-digital converter 11 converts the voltage value V _in and the voltage signal V _RXP into digital signals D _in and D _RXP , which are digital values, respectively. The analog-digital converter 11 is supplied with two reference potentials in the analog-digital conversion from the reference voltage generation circuit 24. Specifically, the analog-digital converter 11 is supplied with reference potentials V _REF1 and V _REF2 from output terminals 25 and 26 of the reference voltage generation circuit 24, respectively.

A selector 12 is connected to the output of the analog-digital converter 11. The selector 12 is output, along with receiving the digital signal _{D in} and _{D RXP} from analog to digital converter 11, in synchronization with the output timing of the control signal SEL3 from the switching control unit 33, the digital signal _{D in} and _{D RXP} to the calculator 13 To do. That is, the selector 12, the analog-digital converter 11 receives the digital signal _{D in} and _{D RXP,} separates and outputs these digital signals subsequent averaging circuit 21a, a 21b. Specifically, the analog-to-digital converter 11, and the digital signal _{D RXP} when the control signal SEL3 = 0, and the digital signal _{D in} the case of the control signal SEL3 = 1 is, is divided by the output time, the selector 12 While receiving the control signal SEL3, the two digital signals D _in and D _RXP that have been time-divided are separated. The selector 12, the digital signal _{D in} the first averaging circuit 21a, and outputs the digital signal _{D RXP} to the second averaging circuit 21b.

The averaging circuits 21a and 21b perform suppression processing using a moving average filter or an IIR filter on the digital signals D _in and D _RXP received from the selector 12. At that time, the averaging circuits 21a and 21b execute the averaging process on the digital signals D _in and D _RXP for m samples (m is an integer of 1 or more) output from the selector 12. The digital signals D _in and D _RXP after the suppression processing are stored in the registers 22a and 22b, respectively.

The arithmetic circuit 23 reads out the digital signals D _in and D _RXP stored in the registers 22a and 22b, and calculates a differential digital value V _D between the digital signals D _in and D _RXP . Then, the arithmetic circuit stores the calculated difference digital value V _{D in} the register 14 as an intensity monitor value of the signal light O _in .

Next, a method for calculating the intensity monitor value of the signal light O _{in in} the signal processing unit 28 will be described.

In the current-voltage converter 31, since the input impedance of the inverting input terminal 20 a of the operational amplifier 20 is extremely large, most of the monitor current I _mon from the current mirror unit 6 is supplied to the resistance element 43. Further, the voltage value _{V in} at the inverting input terminal 20a is the virtual short, a value obtained by adding the input offset voltage ± _{V ofs} to the reference voltage _{V REF3} to the non-inverting input terminal 20b. Therefore, the voltage V _RXP− input to the inverting input of the analog / digital converter 11 when SEL = 1, the voltage V _in− input to the inverting input of the analog / digital converter 11 when SEL = 0, and the analog / digital converter. The voltage V ₊ input to the non-inverting input 11 is given by the following equations (4) to (6).

The analog-digital converter 11 converts the input voltage difference V ₊ −V _RXP− into a digital value D _RXP and _converts the difference V ₊ −V _in− into a digital value D _in . The digital values D _RXP and D _in output from the analog-digital converter 11 are averaged by the averaging circuits 21a and 21b, respectively, and the difference digital value V _D between the digital values D _RXP and D _in is the signal light. It is stored in the register 14 as an intensity monitor value of O _in . Here, assuming that the transfer function of the analog-digital converter 11 is f, the obtained differential digital value V _D is given by the following equation (7).

As described above, in the optical receiver 1b, the photocurrent _Iorg generated _{in the} photodiode 2 corresponding to the input light _Oin is monitored as the monitor current _{Imon, and} is monitored by the current-voltage converter 31. The current I _mon is converted into a voltage signal V _RXP . At this time, in the current-voltage converter 31, most of the monitor current I _mon flows through the resistance element 43 and is converted into the voltage signal V _RXP . In the operational amplifier 20, the inverting input terminal 20a and the non-inverting input terminal 20b are virtually short-circuited, but the input offset voltage V _ofs is generated between the inverting input terminal 20a and the non-inverting input terminal 20b. . That is, with respect to the reference voltage _{V REF3} at the noninverting input terminal 20b, the voltage value _{V in} at the inverting input terminal 20a becomes an input offset voltage contained _{V ofs} value _{V REF3} ± _{V ofs.} Therefore, in the differential signal generator 16, input light _{O in} about monitoring signal _{V D} based on the difference between the voltage signal _{V RXP} from the voltage value _{V REF3} ± _{V ofs} and the output terminal 20c at the inverting input terminal 20a is generated The Therefore, even if the intensity of the signal light O _in is weak and the photocurrent I _org is small by canceling out the influence of the input offset V _ofs of the operational amplifier 20 included in the monitor signal V _D , the monitor signal Accuracy can be improved. Furthermore, the input offset of the operational amplifier is affected by temperature fluctuations and power supply voltage. By subtracting this input offset from the monitor signal, the light intensity can be monitored stably against power supply voltage and temperature fluctuations. .

Also, as in the present embodiment, the optical receiver provides either the voltage signal V _RXP from the voltage value V _in and an output end 20c at the inverting input terminal 20a to selectively difference signal generating section 16 the signal switch 36 is preferably provided with a switching control unit 33 sends a control signal SEL3 for selecting either one of the voltage value V _in and the voltage signal V _RXP to the signal switch 36. Then, the difference signal generating unit 16 is preferably received in response to the voltage value _{V in} the voltage signal _{V RXP} to a control signal SEL3. Thereby, in the difference signal generation unit 16, a circuit (for example, the analog-digital converter 11) for receiving the voltage value V _in at the inverting input terminal 20a and the voltage signal V _RXP from the output terminal 20c can be shared. The circuit scale of the difference signal generator 16 can be reduced. When performing digital processing in the difference signal generating unit 16 as in this embodiment, by digitizing the voltage value V _in and the voltage signal V both a common analog-to-digital converter 11 of the _RXP, to the analog-to-digital converter 11 Since the resulting offset can also be canceled, the accuracy of the monitor signal can be further improved.

(Modification)
FIG. 6 is a diagram illustrating a configuration of an optical receiver 1c as a modification of the optical receiver 1b according to the second embodiment. The optical receiver 1c shown in the figure includes a package 30, a signal processing unit 29, and a limiting amplifier 8. The package 30 accommodates the photodiode 2, the filter circuit 3, the current mirror unit (monitor current generation circuit) 6, the transimpedance amplifier 42, and the amplifier control unit 45. An example of the package 30 is a coaxial CAN package. The transimpedance amplifier 42 is a (pre) amplifier configured to convert the photocurrent I _org from the photodiode 2 into a reception signal and to change the gain-frequency characteristic. The amplifier controller 45 is a circuit for sending an amplifier control signal S _amp for changing the gain-frequency characteristic to the transimpedance amplifier 42.

One of the differences between the optical receiver 1c according to this modification and the optical receiver 1b of the second embodiment is that the current mirror unit 6 is housed in the package 30 together with the photodiode 2. Another difference is that the gain-frequency characteristic of the transimpedance amplifier 42 is variable, and an amplifier control unit 45 for controlling the gain-frequency characteristic is provided. The amplifier control unit 45 is connected to the inverting input terminal 20a of the operational amplifier 20 and the output terminal of the current mirror unit 6, and the reference voltage V _REF3 to the operational amplifier 20 can be changed.

Specifically, the current mirror unit 6 is housed in a package 30, and the output terminal of the current mirror unit 6 and the inverting input terminal 20 a of the operational amplifier 20 are connected to each other via one lead pin (terminal) of the package 30. Has been. The output end of the current mirror unit 6 is also connected to the amplifier control unit 45 in the package 30. Thus, the inverting input terminal 20a of the operational amplifier 20 is connected to the current mirror unit 6 and the amplifier control unit 45 by one lead pin. The input impedance of the amplifier controller 45 is set high, and the inflow of the monitor current I _{mon into} the amplifier controller 45 can be almost ignored.

In addition, the signal processing unit 29 of the present embodiment includes a differential input / output amplifier 35 and a reference voltage generation circuit 37. The reference voltage generation circuit 37 is a circuit that sets two reference potentials in analog-digital conversion in the analog-digital converter 11 and a reference potential in the differential input / output amplifier 35. The reference voltage generation circuit 37 has three output terminals 38 to 40, and outputs the output terminal 38 to a predetermined potential V _REF1 = 1 / 4V _REF and the output terminal 39 to a predetermined potential V _REF2 = 3 / 4V _REF . The terminal 40 is set to a predetermined potential V _REF4 = 1 / 2V _REF . The value of the potential V _REF is appropriately set according to the range of the monitor current I _mon output from the current mirror unit 6 and the resistance value of the resistance element 43. The output terminal 38 of the reference voltage generating circuit 37 is output to one input terminal for setting the reference potential of the analog-digital converter 11, and the output terminal 39 is output to the other input terminal for setting the reference potential of the analog-digital converter 11. The terminal 40 is connected to an input terminal for setting a reference potential of the differential input / output amplifier 35, respectively.

An input terminal 44 is connected to the non-inverting input terminal 20 b of the operational amplifier 20. Although the reference voltage V _REF3 to the operational amplifier 20 is input to the input terminal 44, in the present embodiment, the reference voltage V _REF3 is not supplied from the reference voltage generation circuit 37, and an arbitrary _value is input from the outside of the signal processing unit 29. It can be set to a value. The above equation (5), the voltage value _{V in} at the inverting input terminal 20a of the operational amplifier 20, since the response is to the value of the reference voltage _{V REF3} inputted to the input terminal 44, by changing the reference voltage _{V REF3} It may change the voltage value _{V in.}

In this embodiment, since the inverting input terminal 20a is connected to an amplifier control unit 45, the voltage value V _in is inputted to the amplifier control unit 45. Amplifier controller 45 generates an amplifier control signal _{S # 038} according to the magnitude of the voltage value _{V in.} That is, in the optical receiver 1c, the gain-frequency characteristic of the transimpedance amplifier 42 can be changed by changing the reference voltage _VREF3 input to the input terminal 44. For example, the transimpedance amplifier 42 may have the same internal configuration as that of the current-voltage converter 31. In that case, if the resistance value of the feedback resistor connected between the inverting input terminal and the output terminal of the operational amplifier is variable according to the amplifier control signal S _amp , the transimpedance amplifier 42 capable of changing the gain-frequency characteristics is provided. Easy to configure.

Differential output amplifier 35 is provided for adjusting the potential of the voltage value V _in or voltage signal V _RXP from the signal switch 36. The differential input / output amplifier 35 has a pair of differential input ends and a pair of differential output ends. One of the pair of differential input terminals of the differential input / output amplifier 35 is connected to the signal switch 36, and the other is connected to the input terminal 44. That is, one of the pair of differential input terminals of the differential output amplifier 35, one selectively provide one of the voltage signals V _RXP from the voltage value V _in and an output end 20c at the inverting input terminal 20a Is done. On the other hand, a reference voltage _VREF3 is provided.

  One of the pair of differential output terminals of the differential input / output amplifier 35 is connected to the inverting input terminal of the analog-digital converter 11. The other of the pair of differential output terminals of the differential input / output amplifier 35 is connected to the non-inverting input terminal of the analog-digital converter 11.

The reference voltage V _REF4 is supplied from the reference voltage generation circuit 37 to the input terminal for setting the reference voltage of the differential input / output amplifier 35 as described above. Then, (the center voltage i.e. differential signal) reference voltage of the differential input to the output amplifier 35 the voltage value _{V in} and the voltage signal _{V RXP} is changed to the reference voltage _{V REF4.} The reference voltage V _REF4 is set to, for example, a voltage between the reference voltage V _REF1 and the reference voltage V _REF2 to the analog-digital converter 11 (in this embodiment, _½ V _REF ). Thus, by variation of the reference voltage _{V REF3} to the operational amplifier 20, to correct the variation of the voltage value _{V in} and the voltage signal _{V RXP} potential, the voltage value _{V in} and the voltage signal _{V RXP} size analog-to-digital converter 11 Within the input range.

In the optical receiver 1c according to this modification, the transimpedance amplifier 42 that converts the photocurrent I _org from the photodiode 2 into a received signal is configured to be able to change the gain-frequency characteristics. Thus, for example, when the signal frequency of the received signal is relatively high, the gain of the transimpedance amplifier 42 is lowered to increase the cutoff frequency, and when the signal frequency of the received signal is relatively low, the gain of the transimpedance amplifier 42 is increased. An appropriate gain-frequency characteristic can be selected according to the signal frequency of the received signal, such as increasing the cutoff frequency to lower it.

Further, in the optical receiver 1c according to the present modification, the amplifier controller 45, the gain - the amplifier control signal S _{# 038} for changing the frequency characteristic in accordance with the voltage value V _in at the inverting input terminal 20a of the operational amplifier 20 Is generated. Further, the reference voltage V _REF3 to the operational amplifier 20 can be changed. In the optical receiver 1c, the amplifier controller 45 is connected to the inverting input terminal 20a of the operational amplifier 20, and the reference voltage V _REF3 at the non-inverting input terminal 20b that is in a virtual short-circuit relationship with the inverting input terminal 20a. The amplifier control signal S _amp is generated according to the value. Thereby, since the gain-frequency characteristic of the transimpedance amplifier 42 can be changed using the reference voltage _VREF3 to the operational amplifier 20, a signal input terminal for changing the gain-frequency characteristic of the transimpedance amplifier 42 is independently provided. There is no need to provide it, and the number of input terminals to the circuit can be reduced.

Further, in the optical receiver 1c according to this modification, the photodiode 2, the current mirror unit 6, the transimpedance amplifier 42, and the amplifier control unit 45 are accommodated in the package 30, and the current mirror unit 6 and the amplifier control unit 45 are accommodated. And the inverting input terminal 20 a of the operational amplifier 20 are connected to each other via one terminal (lead pin) of the package 30. As a result, among the lead pins included in the package 30, the lead pin for outputting the monitor current I _mon and the lead pin for inputting a signal to the amplifier control unit 45 can be shared, so the number of lead pins required for the package 30. Can be reduced.

In addition, this invention is not limited to each embodiment mentioned above. For example, in the analog-digital converter 11 of the optical receiver 1a, the input voltage V _RXP is in the range of 1 / 4V _{REF to} 3 / 4V _REF , and the digital value is within the range of “0” to “2 ^N−1 ”. Although the conversion is performed by mapping, the scaling of the analog-digital conversion may be changed at any time. For example, the converted digital value at the time of maximum light input is “2 ^N−1 ”, the converted digital value of the maximum output voltage of the operational amplifier 20 is “100” (in the case of 10-bit resolution), or “1000” ( When the resolution is set to 12 bits, the quantization error after analog-digital conversion can be further reduced.

  Further, the selector 12, the averaging circuits 21a and 21b, the registers 22a, 22b, and the arithmetic circuit 23 may be constructed as separate hardware devices, or as functional components on the same CPU board. It may be constructed.

It is a figure which shows the structure of the optical receiver which is 1st Embodiment of this invention. It is a figure shown in detail about the circuit structure of the signal processing part of FIG. It is a figure which shows the timing chart of each signal processed in the signal processing part of FIG. 1, (a) is a timing chart of a control signal, (b) is a timing chart of the output signal of an operational amplifier, (c) is Timing chart of output signal of analog-digital converter, (d) is a timing chart of data stored in the first register of the arithmetic unit, and (e) is a timing of data stored in the second register of the arithmetic unit. A chart (f) is a timing chart of data stored in the output side register. (A) is a graph which shows the monitoring result of the intensity | strength of the signal light in the conventional optical receiver which does not have a difference signal production | generation part, (b) is a graph which shows the monitoring result of the intensity | strength of the signal light in this embodiment. is there. It is a figure which shows the structure of the optical receiver which is 2nd Embodiment of this invention. It is a figure which shows the structure of the optical receiver which is a modification of 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1a-1c ... Optical receiver, 2 ... Photodiode, 6 ... Current mirror part (monitor current generation circuit) 10, 31 ... Current-voltage converter, 11 ... Analog-digital converter (analog-digital conversion part), 12 ... Selector ( Selector unit), 13 arithmetic unit (arithmetic unit), 15, 33 switching control unit, 16 difference signal generation unit, 17 offset voltage generation circuit, D _RXP (1) first digital signal, D _RXP ( 0) ... second digital signal, V _D ... monitor signal, O _in ... optical signal (input light), S ₁ ... current path switch, V _RXP (1) ... first voltage signal, V _RXP (0) ... Second voltage signal.

Claims (9)

A photodiode that generates a photocurrent corresponding to the input light; and
A monitor current generating circuit that detects the photocurrent and generates a monitor current corresponding to the photocurrent;
A current-voltage converter that receives the monitor current and converts a current signal representing the monitor current into a voltage signal;
A current path switch for connecting and disconnecting a current path of the current signal between the monitor current generating circuit and the current-voltage converter;
A switching control unit for sending a control signal for connecting and disconnecting the current path to the current path switch;
A first voltage signal converted by the current-voltage converter when the current flow path is connected and a second voltage signal converted by the current-voltage converter when the current flow path is cut off according to the control signal. A difference signal generation unit that generates a monitor signal related to the input light based on a difference between the first voltage signal and the second voltage signal;
An optical receiver comprising: A photodiode that generates a photocurrent corresponding to the input light; and
A monitor current generating circuit that detects the photocurrent and generates a monitor current proportional to the photocurrent;
A current-voltage converter that receives the monitor current and converts the monitor current into a voltage signal;
A current path switch interposed in a current path between the monitor current generation circuit and the current-voltage converter;
A switching control unit for sending a control signal to the current path switch;
A first voltage signal converted by the current-voltage converter when the current path is connected and a second voltage signal converted by the current-voltage converter when the current path is disconnected are received according to the control signal. A difference signal generation unit that generates a monitor signal related to the input light based on a difference between the first voltage signal and the second voltage signal;
An optical receiver comprising: An offset voltage generation circuit connected to the current-voltage converter and generating a predetermined offset voltage in the voltage signal;
The optical receiver according to claim 1, wherein the optical receiver is an optical receiver. A photodiode that generates a photocurrent corresponding to the input light; and
A monitor current generating circuit that detects the photocurrent and generates a monitor current corresponding to the photocurrent;
An operational amplifier having a first input terminal connected to the monitor current generation circuit, a second input terminal for inputting a reference voltage, and an output terminal connected to the first input terminal via a feedback resistor; A current-voltage converter configured to convert the monitor current into a voltage signal;
A difference signal generation unit that generates a monitor signal related to the input light based on a difference between a voltage value at the first input terminal of the operational amplifier and the voltage signal from the output terminal;
An optical receiver comprising: A signal switch that selectively provides one of the voltage value at the first input terminal and the voltage signal from the output terminal to the difference signal generation unit;
A switching control unit that sends a control signal for selecting one of the voltage value and the voltage signal to the signal switch;
Further comprising
The difference signal generator is
The optical receiver according to claim 4, wherein the voltage value and the voltage signal are received according to the control signal. An amplifier configured to convert the photocurrent from the photodiode into a received signal and to change a gain-frequency characteristic;
An amplifier control unit for sending an amplifier control signal for changing the gain-frequency characteristic to the amplifier;
Further comprising
The amplifier control unit is connected to the first input terminal of the operational amplifier, and according to the magnitude of the reference voltage at the second input terminal that is in a virtual short-circuit relationship with the first input terminal. 6. The optical receiver according to claim 4, wherein the amplifier control signal is generated. A package that houses the photodiode, the monitor current generation circuit, the amplifier, and the amplifier controller;
The optical receiver according to claim 6, wherein the monitor current generation circuit, the amplifier control unit, and the first input terminal of the operational amplifier are connected to each other via one terminal of the package. . A measurement method for measuring the intensity of an incident light signal,
Generating a monitor current from the output signal of the photodiode;
Generating a reference current from an offset voltage generation circuit;
Detecting the reference current and a current obtained by adding the monitor current and the reference current, and generating a difference signal between the two in a difference signal generation unit;
An incident light signal intensity measuring method comprising: Generating a monitor current from the output signal of the photodiode receiving the incident light signal;
Converting the monitor current into a voltage signal using an operational amplifier in which a feedback resistor is connected between the input terminal and the output terminal;
Generating a monitor signal according to the intensity of the incident light signal based on the difference between the voltage value at the input end and the voltage signal from the output end;
An incident light signal intensity measuring method comprising:

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