JP5599581B2 - Photoelectric conversion device - Google Patents

Description

  The present invention relates to a photoelectric conversion device that receives an optical signal transmitted from an optical transmitter via an optical transmission line in an optical transmission system and converts the optical signal into an electrical signal.

  In recent years, with the progress of optical communication technology, optical transmission systems using optical cables have become widespread. According to this optical transmission system, relayless transmission of about several tens of kilometers can be performed, so that the transmission system can be easily widened. This optical transmission system generally includes an optical transmitter arranged on the sender side and an optical network unit (ONU) as an optical receiver arranged on the receiver side by an optical cable. It is configured to be connected through a configured long-distance optical transmission line. Then, the transmitter side mixes the TV signal and the announcement broadcast signal, converts the mixed electric signal into an optical signal by the optical transmitter, and transmits the optical signal to the optical line terminating device via the optical transmission line. . In this optical line termination device, an optical signal is converted into an electric signal (RF signal) and output to a TV receiver. This photoelectric conversion device incorporates a PD (Photo Diode) for converting an optical signal into an electric signal. By applying a reverse voltage to the PD, the light intensity change of the light energy incident on the PD is changed. A proportional current (reverse current) flows and photoelectric conversion can be performed.

  Here, in a broadcasting system that performs emergency notification broadcasting, a system capable of continuing the notification broadcasting even in the event of a power failure due to a disaster or the like is required. However, when the power supply to the photoelectric conversion device is stopped due to a power failure, the reverse voltage is not applied to the PD, so that the photoelectric conversion cannot be performed. In order to prevent such a situation, it has been proposed that a dry cell or a large-capacity capacitor is built in a photoelectric conversion device as a backup power source, and photoelectric conversion can be continued by applying a reverse voltage even during a power failure ( For example, see Patent Document 1).

  However, when a dry cell is used as a backup power source, there is a problem that it takes time to maintain the dry cell. Therefore, the PD is used in a non-bias mode (solar cell mode) without applying a reverse voltage and output from this PD. It has been proposed to perform photoelectric conversion without using a dry cell by outputting a signal to be output via an output terminal (see, for example, Patent Document 2).

  In such a photoelectric conversion device capable of performing photoelectric conversion in the no-bias mode, for example, when transmitting a CATV signal, during power feeding, broadcast signals of all channels are transmitted with high quality that satisfies the required performance, and no power is fed. In some cases, only FM band broadcast signals for performing emergency notification broadcasts or the like are transmitted as FM signals satisfying the required performance. However, in this case, many distortion components of each channel fall into the FM signal, and there is a problem that the DU ratio of the FM signal is lowered.

  Therefore, the inventor of the present application improves the DU ratio of an electrical signal in a predetermined band in a photoelectric conversion apparatus that outputs an electrical signal in a predetermined band such as an FM signal by performing photoelectric conversion in a no-bias mode when no power is supplied. (For example, refer to Patent Document 3. However, the invention described in Patent Document 3 has not been disclosed at the time of filing this application).

  FIG. 5 shows a circuit diagram of a conventional photoelectric conversion device described in Patent Document 3. This photoelectric conversion device (optical receiver) 100 is configured by connecting a PD 101 that performs photoelectric conversion, an RF output terminal 102 that outputs an RF signal, and an FM output terminal 103 that outputs an FM signal via a line. Has been. An amplifier A100 is connected to the anode side of the PD 101, and the above-described RF output terminal 102 is connected to the output stage side of the amplifier A100. A coil L100 and a resistor R100 are connected to the anode side of the PD 101, and a capacitor C100 and a control circuit 104 are connected between the coil L100 and the resistor R100, respectively. A positive power source + Vc is connected to the cathode side of the PD 101 via a resistor R200. Capacitors C200 and C300 are connected to both ends of the resistor R200. Further, the optical receiver 100 is provided with a short circuit 105 (a transmission line along the one-dot chain line shown in FIG. 3) for short-circuiting the cathode side and the anode side of the PD 101. In the short circuit 105, an FM MBEF (FM Band Eliminate Filter) 106 and a switch 107 are connected in series to the PD 101, and a coil L200 is connected in parallel to the FMBEF 106. This FMBEF 106 is an attenuating means for attenuating an electric signal in a predetermined band (here, FM signal; the same applies hereinafter). The switch 107 is an opening / closing means for closing the short circuit 105 only when no reverse voltage is supplied. An FMBPF (FM Band Pass Filter) 108 is connected to the cathode side of the PD 101 in the short circuit 105 configured as described above. The FMBPF 108 is a filtering unit that outputs an electric signal in a predetermined band.

  In the photoelectric conversion device 100, when no power is supplied, the PD 101 can be short-circuited by closing the switch 107, and only the FM signal is extracted from the signals output from the PD 101 in the no-bias mode, and the FM signal is output from the FM output terminal 103. It becomes possible to output. In particular, in the photoelectric conversion device 100, only the electrical signals of unnecessary channels that can be included in the FM signal are short-circuited by using the short circuit 105, thereby preventing distortion components of these electrical signals from falling into the FM signal. , The DU ratio of the FM signal can be improved.

JP 2006-174221 A JP 2008-78988 A Japanese Patent Application No. 2008-234221

  However, although the photoelectric conversion apparatus 100 described in Patent Document 3 can output an FM signal having a high DU ratio, there is still room for improvement in terms of the output size of the FM signal. That is, in this photoelectric conversion apparatus 100, an unnecessary channel electrical signal that can be included in the FM signal can be short-circuited using the short circuit 105, but some of the other signals including the FM signal are partially included. Although output from the FM output terminal 103, the other part is not output from the FM output terminal 103, but is a transmission path 109 (a transmission path from the ground of the amplifier A100 to the PD 101 via the capacitor C300, as shown in FIG. The transmission path along the chain line) is refluxed. Both high-frequency signal (RF signal) and low-frequency signal (FM signal) circulate in this transmission path 109, and FM output from the FM output terminal 103 is equivalent to the circulated low-frequency signal (FM signal). The signal output will decrease.

  The present invention has been made in view of the above, and in a photoelectric conversion device that outputs an electric signal of a predetermined band such as an FM signal by photoelectric conversion, the output of the electric signal of the predetermined band can be further improved. It is an object to provide a photoelectric conversion device that can be used.

In order to solve the above-described problems and achieve the object, the photoelectric conversion device according to claim 1 is a photoelectric conversion device that converts an optical signal into an electric signal in an optical transmission system, and converts the optical signal into the electric signal. A photodiode to be converted into a signal, a high-frequency signal output means for outputting a predetermined high-frequency signal among the electrical signals output from the photodiode, and a predetermined low-frequency signal among the electrical signals output from the photodiode A low-frequency signal output means for outputting a high-frequency signal; a matching means for performing impedance matching between an external device connected to the low-frequency signal output means; and a part of the electric signal output from the photodiode and the high frequency signal output hands stage, before Symbol low frequency signal output means, and a transmission path for returning to the photodiode without going through the alignment means, the high frequency A high-frequency transmission line capable of returning only the signal, a low-frequency transmission line capable of returning only the low-frequency signal, and a short-circuit path capable of returning signals not to be returned to the high-frequency transmission line and the low-frequency transmission line. A short circuit that short-circuits the cathode side and the anode side of the photodiode only when no power is supplied to the photoelectric conversion device, and a current shunting to the low-frequency signal output means out of the current output from the photodiode Current adjusting means for adjusting the ratio.

According to the photoelectric conversion device of the first aspect, the high-frequency transmission line and the low-frequency transmission line are provided, and the current adjustment means is provided in the low-frequency transmission line to adjust the current shunt ratio to reach the low-frequency signal output means. As a result, the low-frequency signal output from the low-frequency signal output means can be increased. In addition, since the high-frequency transmission line and the low-frequency transmission line are provided in this way, the high-frequency signal is returned to the photodiode via the high-frequency transmission line, so that the high-frequency signal passes through the current adjusting means. Can be avoided.
In addition, by providing the matching means, it is possible to achieve impedance matching with the subsequent stage device by the matching means, so that the resistance value of the current adjusting means can be increased by separating from impedance matching.

It is a circuit diagram of the optical receiver which concerns on Embodiment 1 of this invention. It is a figure which shows typically the flow of the signal at the time of the no-power supply in the circuit of FIG. 6 is a circuit diagram of an optical receiver according to Embodiment 2. FIG. It is a figure which shows typically the flow of the signal at the time of the no-power supply in the circuit of FIG. It is a circuit diagram of the conventional photoelectric conversion apparatus.

  Embodiments of a photoelectric conversion device according to the present invention will be described below in detail with reference to the accompanying drawings. However, the present invention is not limited by this embodiment.

[I] Embodiment 1
First, Embodiment 1 of the present invention will be described.

〔Constitution〕
The configuration of the optical receiver according to the first embodiment will be described. FIG. 1 is a circuit diagram of an optical receiver according to the first embodiment. The optical receiver 1 includes a PD 2 that performs photoelectric conversion, an RF output terminal 3 that is a high-frequency signal output unit that outputs a predetermined high-frequency signal (hereinafter referred to as an RF signal), and a predetermined low-frequency signal (hereinafter referred to as an FM). Signal), which is a low-frequency signal output means, and is connected to each other via a line as shown.

  A positive power source + Vc is connected to the cathode side of PD2 through a matching circuit 5 which is a matching means constituted by a coil L1 and a coil L2. That is, when the matching circuit 5 is not provided, when viewed from the FM output terminal side, a resistor R1 described later becomes an internal impedance of the optical receiver 1, and this internal impedance is converted to an internal impedance (for example, an external device) In the case of a TV, it is necessary to set the resistance to 75Ω), and it becomes difficult for the resistor R1 to exert a function as a current adjusting means described later. For this reason, by providing the matching circuit 5, it is possible to increase the resistance value of the resistor R <b> 1 and to exhibit the function as the current adjusting means. The elements constituting the matching circuit 5 are not limited to the coil L1 and the coil L2, and any elements can be used as long as they have a matching function. For example, a transformer can be used instead.

  Between the coil L1 and the coil L2, the above-described FM output terminal 4 is connected through an FM BPF (FM Band Pass Filter) 6. A coupling capacitor C3 is connected between the positive power source + Vc and the matching circuit 5, and the capacitor C3 is grounded.

  On the other hand, the amplifier A1 is connected to the anode side of the PD2, and the above-described RF output terminal 3 is connected to the output stage side of the amplifier A1. Further, a coil (choke coil) L3 and a resistor R2 are connected to the anode side of the PD 2, and a control circuit 7 for controlling the optical receiver 1 is connected between the coil L3 and the resistor R2. Yes.

  Further, the optical receiver 1 is provided with a short circuit 8 for short-circuiting the cathode side and the anode side of the PD 2. In this short circuit 8, a coil L4 and a switch 9 are connected in series with respect to PD2. The switch 9 is an opening / closing means for closing the short circuit 8 only when no reverse voltage is supplied.

  Here, a resistor (matching resistor) R1 and a capacitor (coupling capacitor) C1 are connected in series on the cathode side of PD2, and this capacitor C1 is grounded. The resistor R1 is a current adjusting means for adjusting the current shunt ratio of the current output from the PD2 to the FM output terminal 4. By using a resistor having a large resistance value as the resistor R1, the current reaching the FM output terminal 4 can be made larger than the current passing through the low-frequency transmission line 11 described later. The output of the FM signal can be increased. For this reason, it is preferable to use a resistor having a resistance value as large as possible as the resistor R1. Capacitor C1 is a low-frequency signal passing means for combining and passing at least a low-frequency signal out of a part of the electrical signal output from PD2. For this reason, as the capacitor C1, a capacitor having a larger capacity than C2, which will be described later, is used so that the impedance is low in a low frequency range. However, since the function of the capacitor C1 is to pass a low-frequency signal, other means may be arranged instead of the capacitor C1 or an arbitrary low-pass filter may be arranged as long as the equivalent function is achieved. . Furthermore, since the high-frequency signal is allowed to pass through the capacitor C2, which will be described later, the capacitor C1 may be configured to pass signals in other bands as long as the low-frequency signal is allowed to pass.

  Further, a capacitor (coupling capacitor) C2 is connected in series to the cathode side of PD2, and this capacitor C2 is grounded. The capacitor C2 is a high-frequency signal passing means for combining and passing only a high-frequency signal out of a part of the electrical signal output from the PD2. For this reason, a capacitor having a small capacitance of several pF is used as the capacitor C2 so that it has a high impedance in the low band and a low impedance in the high band. However, since the function of the capacitor C2 is to pass a high-frequency signal, other means may be disposed instead of the capacitor C2 or an arbitrary high-pass filter may be disposed as long as the equivalent function is achieved. .

[Operation-Power supply]
Next, the operation of the circuit thus configured will be described. At the time of feeding the positive power source + Vc, the switch 9 is in an open state, a reverse voltage fed from the positive power source + Vc is applied to the PD 2, photoelectrically converted by the PD 2, and an electrical signal is output. The FM signal output from the output terminal 3 and passed through the FMBPF 6 is output from the FM output terminal 4.

[Operation-No power supply]
FIG. 2 is a diagram schematically showing a signal flow when no power is supplied in the circuit of FIG. When the positive power supply + Vc is in a non-powered state due to a power failure or the like, if light energy exceeding the energy band cap is incident on the PD 2 driven in the no-bias mode, this light energy is absorbed by the depletion layer and is conducted. By generating and drifting electrons and holes, an electromotive force proportional to the light intensity is generated. At the time of no power feeding, the switch 9 is closed by a known method, so that the short circuit 8 is formed.

  Further, in the circuit of FIG. 2, in addition to the short circuit 8 as in the prior art, a part of the electrical signal output from the PD 2 is returned to the PD 2 without passing through the RF output terminal 3 and the FM output terminal 4. A high-frequency transmission line 10 that can return only an RF signal and a low-frequency transmission line 11 that can return an FM signal are formed.

  For this reason, the electrical signal output from the PD 2 is not only an RF signal output from the RF output terminal 3 and an FM signal output from the FM output terminal 4, but also a signal that circulates through the high-frequency transmission line 10 and low-frequency transmission. It becomes a signal that circulates through the path 11 or a signal that circulates through the short circuit 8.

Specifically, the RF signal transmitted from the amplifier A1 to the ground side without being output from the RF output terminal 3 does not pass through the capacitor C1 having a high impedance at a high frequency, and is a capacitor having a low impedance at a high frequency. Since it passes through only C2 and is returned to the cathode side of PD2, it becomes a signal that returns through the high-frequency transmission line 10. In particular, since the RF signal passes only through the capacitor C2 of the high-frequency transmission line 10 and does not pass through the resistor R1 of the low-frequency transmission line 11, it is possible to prevent the RF signal from being lost by the resistor R1.

Further, the FM signal transmitted from the amplifier A1 to the ground side without being output from the FM output terminal 4 does not pass through the capacitor C2 having high impedance in the low frequency range, and only passes through the capacitor C1 having low impedance in the low frequency range. Since it passes through and is recirculated to the cathode side of PD2, it becomes a signal that recirculates through the low-frequency transmission line 11.

  Further, these signals that do not return to the high-frequency transmission line 10 or the low-frequency transmission line 11 circulate through the short circuit 8 as unnecessary signals, so that only the electric signals of unnecessary channels are short-circuited and the voltage of the channel is connected to the photodiode itself. Therefore, distortion due to the electrical signal does not occur. Therefore, the distortion component of these electric signals is prevented from falling into the electric signal in the FM band.

〔effect〕
As described so far, according to the first embodiment, the high-frequency transmission line 10 and the low-frequency transmission line 11 are provided, and the low-frequency transmission line 11 is provided with the resistor R1 to shunt the current reaching the FM output terminal 4 By adjusting the ratio, the FM output from the FM output terminal 4 can be increased. Since the high-frequency transmission line 10 and the low-frequency transmission line 11 are provided in this way, the RF signal is returned to the PD 2 via the high-frequency transmission line 10 so that the RF signal passes through the resistor R1. The loss that occurs can be avoided.

  In addition, by providing the matching circuit 5, it is possible to achieve impedance matching with the subsequent device by the matching circuit 5, and therefore, it is possible to increase the resistance value of the resistor R1 separately from impedance matching. .

[II] Embodiment 2
Next, a second embodiment of the present invention will be described. However, unless otherwise specified, the configuration and processing shown in the second embodiment are the same as the configuration and processing shown in the first embodiment, and the same contents as the configuration and processing shown in the first embodiment are necessary. Accordingly, the same reference numerals as those used in the description of the first embodiment are used, and the description thereof is omitted.

〔Constitution〕
FIG. 3 is a circuit diagram of the optical receiver 20 according to the second embodiment. This optical receiver 20 is obtained by replacing the connection polarity of the RF output terminal 3 and the FM output terminal 4 with respect to the PD 2 with respect to the configuration of the optical receiver 1 according to Embodiment 1 shown in FIG. That is, the amplifier A1 is connected to the cathode side of the PD2, and the RF output terminal 3 is connected to the output stage side of the amplifier A1. On the other hand, the matching circuit 5 is connected to the anode side of the PD 2, and the FM output terminal 4 is connected between the coil L 1 and the coil L 2 of the matching circuit 5 via the FMBPF 6. Further, on the anode side of PD2, a resistor R1 and a capacitor C1 are connected in series, and a capacitor C2 is connected in series.

  In addition, on the cathode side of PD2, a resistor R3 is provided between the connection point of the capacitor C3 and the connection point of the amplifier A1 on the line from the positive power source + Vc to PD2. On the anode side of PD2, a capacitor C4 is connected between the matching circuit 5 and the resistor R2, and the capacitor C4 is grounded.

[Operation-Power supply]
The circuit configured as described above operates in the same manner as in the first embodiment. That is, at the time of power feeding, the switch 9 is in an open state, a reverse voltage fed from the positive power source + Vc is applied to the PD 2, photoelectrically converted by the PD 2 and an electrical signal is output, and this electrical signal is output to the RF output terminal. 3 and an FM signal that has passed through the FM PPF 6 is output from the FM output terminal 4.

[Operation-No power supply]
FIG. 4 is a diagram schematically showing a signal flow when no power is supplied in the circuit of FIG. When no power is supplied, the switch 9 is closed to form the short circuit 8. In addition to the RF signal output from the RF output terminal 3 and the FM signal output from the FM output terminal 4, the electrical signal output from the PD 2 includes a signal that circulates through the high-frequency transmission line 10 and a low-frequency transmission line. 11 is a signal that circulates through 11 or a signal that circulates through the short circuit 8.

〔effect〕
As described above, according to the second embodiment, even if the connection polarity of the RF output terminal 3 and the FM output terminal 4 with respect to the PD 2 is changed, the optical receiver 20 is configured, and the same effect as that of the first embodiment is obtained. Can be obtained.

[Modification]
Although the embodiments of the present invention have been described above, the specific configuration and means of the present invention may be arbitrarily modified and improved within the scope of the technical idea of each invention described in the claims. Can do. Hereinafter, some of such modifications will be described.

(About problems to be solved and effects of the invention)
First, the problems to be solved by the invention and the effects of the invention are not limited to the above-described contents, and the present invention solves the problems not described above or has the effects not described above. There are also cases where only some of the described problems are solved or only some of the described effects are achieved.

(Other circuit configurations)
The circuit configuration described above is an example, and can be arbitrarily changed using a known technique. For example, an FM signal output may be improved when no power is supplied by providing a transformer of an appropriate size in front of the FM output terminal 4.

1, 20, 100 Optical receiver 2, 101 PD
3, 102 RF output terminal 4, 103 FM output terminal 5 Matching circuit 6, 108 FMBPF
7, 104 Control circuit 8, 105 Short circuit 9, 107 Switch A1, A100 Amplifier R1, R2, R3, R100, R200 Resistors L1, L2. L3, L100, L200 Coil C1, C2, C3, C4, C100, C200, C300 Capacitor + Vc Positive power supply 106 FMBEF
109 Transmission line

Claims (1)

A photoelectric conversion device for converting an optical signal into an electrical signal in an optical transmission system,
A photodiode for converting the optical signal into the electrical signal;
Of the electrical signal output from the photodiode, high-frequency signal output means for outputting a predetermined high-frequency signal,
Of the electrical signal output from the photodiode, low-frequency signal output means for outputting a predetermined low-frequency signal,
Matching means for performing impedance matching with an external device connected to the low-frequency signal output means;
Some of the electric signal output from the photodiode, the high frequency signal output hands stage, before Symbol low frequency signal output means, and a transmission path for returning to the photodiode without going through the alignment means, A high-frequency transmission line capable of returning only the high-frequency signal, a low-frequency transmission line capable of returning only the low-frequency signal, and a short circuit capable of returning a signal which does not return to the high-frequency transmission line and the low-frequency transmission line. A short circuit that short-circuits the cathode side and the anode side of the photodiode only when no power is supplied to the photoelectric conversion device,
Of the current output from the photodiode, current adjusting means for adjusting a current shunt ratio to the low-frequency signal output means;
A photoelectric conversion device comprising:

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