JPH09116497A - Optical receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress deterioration in the output characteristic of a reception circuit amplifying the signal of a high frequency band by connecting a bypass circuit to a photodiode receiving light signals which are frequency-multiplexed. SOLUTION: The light signal of a frequency band A and the light signal of a frequency band B, which are frequency-multiplexed, are optically inputted to the photodiode 10 and are converted into electric signals. The electric signal of the frequency band A is connected to a cathode-side terminal K, is amplified by a reception circuit and is outputted from an output terminal 14. At the same time, the electric signal of a frequency (b) is connected to an anode-side terminal A and is outputted from the output terminal through a receiver 16. Since the bypass circuit 20 whose one end is grounded is connected to the cathode-side terminal K at that time, the electric signal whose frequency is higher than the frequency band A escapes to ground potential. Thus, the signal is prevented from appearing in the input of the reception circuit 16 and the input signal level of the reception circuit 16 is prevented from being deteriorated. Then, the output signal intensity of the reception circuit 16 is not deteriorated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical receiver used for receiving optical communication, and more particularly to an optical receiver used in an analog communication system for receiving a frequency-multiplexed optical signal for each predetermined frequency band. The present invention relates to a band division type optical receiver that performs amplification.

[0002]

2. Description of the Related Art In an optical communication system, particularly an analog communication system, signals of different modulation systems such as a signal of frequency band A of AM modulation system and a signal of frequency band B of FM modulation system are frequency-multiplexed and transmitted. The frequency-multiplexed transmission method that has been put into practical use In such a communication system, the specifications relating to the signal quality are different for each modulation system, and therefore, it is necessary for the receiver side to divide the frequency band into the frequency band A and the frequency band B for amplification. In this case, a photodiode that converts an optical signal into an electrical signal can be considered as a current source that ideally flows a current proportional to the light intensity, so that it is used for different frequency bands on the anode side and the cathode side of the photodiode. By connecting the receiving circuit of No. 2 to each other, the two receiving circuits can amplify the electric signal of each frequency band independently of each other.

Therefore, as shown in FIG. 7, it is connected to a photodiode 10 for receiving an optical signal and converting it into an electric signal, and a cathode side terminal K of this photodiode 10.
Of the optical signals received by the photodiode 10, a receiving circuit 12 that amplifies an electrical signal corresponding to the optical signal in the frequency band A, an output terminal 14 that outputs the electrical signal amplified by the receiving circuit 12, and a photodiode A receiving circuit 16 connected to the anode-side terminal A of 10 and amplifying an electric signal corresponding to the optical signal of the frequency band B among the optical signals received by the photodiode 10, and the receiving circuit 16
A band-division type optical receiver composed of an output terminal 18 for outputting an electric signal amplified by is proposed (Australia Patents Act 1990 “An Optical Reciever”).
According to this band division type optical receiver, the optical signal of the frequency band A and the frequency band B transmitted by frequency multiplexing as shown in FIG. When the light signal is optically input to the optical signal, the optical signal is converted into an electric signal by the photodiode 10. Then, the electric signal corresponding to the optical signal in the frequency band A is amplified by the receiving circuit 12 and is shown in FIG. Such an electric signal is output from the output terminal 14. Further, the electric signal corresponding to the optical signal in the frequency band B is amplified by the receiving circuit 16 and output as an electric signal as shown in FIG.
It is supposed to be output from.

[0004]

However, in the actual photodiode 10 which constitutes the band division type optical receiver shown in FIG. 7, the capacitance Cj is formed at the semiconductor junction inside the diode.
As shown in the equivalent circuit diagram of FIG. 9, this capacitance Cj is in parallel with the current source 22. Therefore, even if a photodiode for high-speed optical communication is used, for example, 50
When the frequency rises to about 0 MHz, the decrease in internal impedance cannot be ignored. That is, a part of the input signal level of the receiving circuit 12 appears at the input of the receiving circuit 16 via the capacitor Cj. The phase of the signal appearing via the capacitance Cj is different from the phase of the signal output from the cathode side of the photodiode 10 to the receiving circuit 16, so that the input signal level of the receiving circuit 16 is lowered.

Therefore, the output characteristics of the band-division type optical receiver in which the receiving circuit 12 and the receiving circuit 16 are connected to the cathode side and the anode side of the photodiode 10, respectively, are shown in FIG. As compared with the output characteristic in the case of being connected to No. 10, as shown in FIG. 10, there is a change in the output signal strength of the receiving circuit 12 that amplifies the signal of the AM modulation system of the frequency band A arranged on the low frequency side. Although not seen, the output signal strength of the receiving circuit 16 that amplifies the signal of the FM modulation system in the frequency band B arranged on the high frequency side is deteriorated as the frequency is increased.

That is, in the conventional band division type optical receiver, a part of the input signal level of the receiving circuit 12 for amplifying the signal in the low frequency band is a part of the capacitance Cj of the photodiode 10.
Appears at the input of the receiving circuit 16 that amplifies a signal in the high frequency band via, and lowers the input signal level of the receiving circuit 16, thereby deteriorating the output characteristics of the receiving circuit 16 that amplifies the signal in the high frequency band. There was a problem.
Therefore, there has been a problem how to suppress the deterioration of the output characteristic of the receiving circuit 16 that amplifies the signal in the high frequency band and how to approach the output characteristic when the receiving circuit 16 is solely connected to the photodiode 10.

The present invention has been made in view of the above situation, and when receiving a frequency-multiplexed optical signal and performing amplification for each predetermined frequency band, reception for amplifying a signal in a high frequency band is performed. An object of the present invention is to provide an optical receiver capable of suppressing deterioration of output characteristics of a circuit.

[0008]

The optical receiver of the present invention comprises:
(A) a photodiode that receives an optical signal in a wide frequency band and converts it into an electrical signal; and (b) a first frequency of the optical signal received by the photodiode that is connected to the first terminal of the photodiode. A first receiving circuit that amplifies an electric signal corresponding to an optical signal of a band and outputs the amplified electric signal to a first output terminal; and (c) is connected to a second terminal of the photodiode,
A second receiving circuit that amplifies an electric signal corresponding to an optical signal in a second frequency band higher than the first frequency band in the optical signal received by the photodiode and outputs the amplified signal to a second output terminal. And (d) a bypass circuit connected to the first terminal of the photodiode and allowing an electric signal having a frequency higher than a predetermined frequency to escape to the ground potential.

In the optical receiver of the present invention, the first receiving circuit for amplifying the electric signal corresponding to the optical signal in the first frequency band is connected to the first terminal of the photodiode, and the first frequency band A second receiving circuit that amplifies an electric signal corresponding to an optical signal of a second frequency band on a higher frequency side is connected to a second terminal of the photodiode, and an electric signal having a frequency higher than a predetermined frequency is grounded. Since the bypass circuit that escapes to the first terminal of the photodiode is connected to the first terminal of the photodiode, the first terminal of the photodiode is grounded in terms of high frequency, and thus is input to the first receiving circuit. An electric signal having a frequency higher than the first frequency band escapes to the ground potential through the bypass circuit. Therefore, a signal of a higher frequency than the first frequency band input to the first receiving circuit appears at the input of the second receiving circuit via the semiconductor junction capacitance inside the photodiode, and It is possible to prevent the input signal level from dropping,
Therefore, the deterioration of the output characteristic of the second receiving circuit that amplifies the signal in the high frequency band can be suppressed.

As a bypass circuit of the optical receiver of the present invention,
A capacitor connected in series, an inductor, and a resistor, and a second capacitor connected in series to the first capacitor, one end of the capacitor connected to the first terminal of the photodiode, and one end of the resistor and the first capacitor connected to the first terminal of the photodiode. A bypass circuit in which one end of the two capacitors is grounded can be preferably used.

Also, a capacitor is provided as a bypass circuit,
A bypass circuit in which one end of this capacitance is connected to the first terminal of the photodiode and the other end is grounded can also be suitably used.

The first terminal of the photodiode may be the cathode side terminal of the photodiode, and the second terminal of the photodiode may be the anode side terminal of the photodiode. May be the anode side terminal of the photodiode, and the second terminal of the photodiode may be the cathode side terminal of the photodiode.

[0013]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a block diagram showing a band division type optical receiver according to an embodiment of the present invention.

As shown in FIG. 1, a band division type optical receiver according to an embodiment of the present invention comprises: (a) a photodiode 1 for receiving an optical signal in a wide frequency band and converting it into an electric signal.
0, and (b) the cathode side terminal K of the photodiode 10.
Of the optical signals received by the photodiode 10 and amplifying an electrical signal corresponding to the optical signal in the frequency band A, and (c) an output for outputting the electrical signal amplified by the receiving circuit 12. A receiving circuit 16 that is connected to the terminal 14 and (d) the anode-side terminal A of the photodiode 10 and amplifies an electrical signal corresponding to the optical signal in the frequency band B among the optical signals received by the photodiode 10.
And (e) an output terminal 18 for outputting the electric signal amplified by the receiving circuit 16, and (f) a photodiode 10
A bypass circuit 20 connected to the cathode terminal K of the bypass circuit 20 for releasing an electric signal having a frequency higher than a predetermined frequency to the ground potential.
And

Next, the operation of the band division type optical receiver shown in FIG. 1 will be described.

FIG. 2 is a graph showing a frequency-multiplexed optical signal input to the photodiode of the band division type optical receiver of FIG. 1, and FIG. 3 is an output terminal of the band division type optical receiver of FIG. It is a graph which shows the electric signal output. As shown in FIG. 2, an optical signal in the frequency band A of the AM modulation system and an optical signal in the frequency band B of the FM modulation system, which are frequency-multiplexed by the frequency multiplexing transmission system, are transferred to the photodiode 10
Light is input to. This optical signal is then converted into an electrical signal by the reverse biased photodiode 10.

Next, of the electric signals, the electric signal corresponding to the optical signal in the frequency band A is the photodiode 1.
The signal is amplified by the receiving circuit 12 connected to the cathode side terminal K of 0 and output from the output terminal 14. At the same time, the electric signal corresponding to the optical signal of the frequency band B is connected to the anode side terminal A of the photodiode 10 and is received by the receiving circuit 16
Is amplified and output from the output terminal 18.

At this time, the bypass circuit 2 having one end grounded
Since 0 is connected to the cathode side terminal K of the photodiode 10 and the cathode side terminal K of the photodiode 10 is grounded in terms of high frequency, the frequency band of the electric signal input to the receiving circuit 12 is An electric signal having a higher frequency than A escapes to the ground potential through the bypass circuit 20. Therefore, an electric signal having a frequency higher than the frequency band A input to the receiving circuit 12 does not appear at the input of the receiving circuit 16 via the capacitance Cj of the photodiode 10, and therefore the input signal level of the receiving circuit 16 is lowered. Therefore, the output signal strength of the receiving circuit 16 does not deteriorate unlike the conventional band division type optical receiver.

Thus, the output characteristic of the band division type optical receiver provided with the receiving circuit 12 for amplifying the signal of the AM modulation system of the frequency band A and the receiving circuit 16 for amplifying the signal of the FM modulation system of the frequency band B is shown in FIG. As shown in 3, the receiving circuit 1
2 or the receiving circuit 16 has an output signal strength almost equal to the output signal strength when it is connected to the photodiode 10 independently.

The bypass circuit 20 shown in FIG. 1 is connected to the cathode side terminal K of the photodiode 10 like the receiving circuit 12, but the receiving circuit 12 that amplifies the signal of the frequency band A is the photodiode 10. When the receiving circuit 16 connected to the anode side terminal A of the photodiode 10 for amplifying the signal in the frequency band B higher than the frequency band A is connected to the cathode side terminal K of the photodiode 10, the bypass circuit 20 is As with the receiving circuit 12, it may be connected to the anode side terminal A of the photodiode 10.
Also in this case, the same effect as that shown in FIG. 3 can be obtained.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a bypass circuit which characterizes the band division type optical receiver shown in FIG. 1 will be described below with reference to the accompanying drawings. In the description of the drawings, the same elements as those of the band-splitting optical receiver of FIG. 1 are designated by the same reference numerals, and duplicated description will be omitted.

First, the bypass circuit according to the first embodiment will be described with reference to FIG. Here, FIG. 4 is a circuit block diagram showing a band division type optical receiver having a bypass circuit according to the first embodiment.

As shown in FIG. 4, the bypass circuit 20 according to the present embodiment has a capacitance C ₁ connected in series, an inductor L, and a capacitance C ₃ connected in series with a resistor R and a capacitance C _1.
It is composed of One end of the capacitance C ₁ is connected to the cathode side terminal K of the photodiode 10 and the resistance R
And one end of the capacitor C ₃ are grounded. The receiving circuit 12 and the receiving circuit 16 are connected to the cathode side terminal K and the anode side terminal A of the photodiode 10, respectively, as in the case shown in FIG.

In this way, the bypass circuit 20 is connected in series to the capacitor C ₁ , the inductor L, the resistor R, and the capacitor C _1.
Since it functions as a filter that passes only an electric signal having a frequency higher than a predetermined frequency by being configured with the capacitor C ₃ connected in series with the input signal, the signal is input to the receiving circuit 12 as described above. It becomes possible to let an electric signal having a frequency higher than the frequency band A escape to the ground potential.

Therefore, according to this embodiment, as in the case shown in FIG. 3, the receiving circuit 1 for amplifying the signal in the frequency band A is used.
The output characteristic of the receiving circuit 16 that amplifies the signal of 2 and the frequency band B can be made almost the same as the output characteristic when the receiving circuit 12 or the receiving circuit 16 is individually connected to the photodiode 10.

Although the capacitor C ₁ forming the bypass circuit 20 shown in FIG. 4 is connected to the cathode side terminal K of the photodiode 10 as in the receiving circuit 12, the receiving circuit for amplifying the signal in this frequency band A is used. When the circuit 12 is connected to the anode side terminal A of the photodiode 10 and the receiving circuit 16 for amplifying the signal of the frequency band B higher than the frequency band A is connected to the cathode side terminal K of the photodiode 10. The capacitor C ₁ forming the bypass circuit 20 may be connected to the anode side terminal A of the photodiode 10 as in the receiving circuit 12. Also in this case, the same effect as that of the first embodiment can be obtained.

Next, a bypass circuit according to the second embodiment will be described with reference to FIGS. 5 and 6. Here, FIG.
Is a circuit block diagram showing a band-division type optical receiver having a bypass circuit according to the second embodiment, and FIG. 6 is a graph showing an output characteristic of the band-division type optical receiver of FIG.

As shown in FIG. 5, the bypass circuit 20 according to this embodiment is composed only of a capacitor C ₂ having one end connected to the cathode side terminal K of the photodiode 10 and the other end grounded. . The receiving circuit 12 and the receiving circuit 16 are connected to the cathode side terminal K and the anode side terminal A of the photodiode 10, respectively, as in the case shown in FIG.

Since the bypass circuit 20 is composed of only a single capacitor C ₂ as described above, the frequency band A
When the frequency band B is away from the frequency band B, the same effect as that of the first embodiment can be obtained. That is, if the input impedance of the receiving circuit 12 is Z,
By selecting a capacitance C ₂ that satisfies 1 / ωC ₂ > | Z | in the frequency band A and 1 / ωC ₂ <| Z | in the frequency band B, the frequency band A
The deterioration of the frequency characteristic occurring in the transition region between the frequency band A and the frequency band B can be distributed to each of the frequency band A and the frequency band B within an allowable range.

Therefore, according to this embodiment, as shown in FIG. 6, the high frequency side of the output signal of the frequency band A of the receiving circuit 12 and the low frequency side of the output signal of the frequency band B of the receiving circuit 16 are provided. In the above, although the signal strength slightly deteriorates, the output characteristics can be made substantially the same as when the receiving circuit 12 or the receiving circuit 16 is independently connected to the photodiode 10. This means that the single capacitance C ₂
Considering that the bypass circuit is configured only by itself, it can be said to be an extremely realistic solution.

Although the capacitor C ₂ forming the bypass circuit 20 shown in FIG. 5 is connected to the cathode side terminal K of the photodiode 10 as in the receiving circuit 12, the receiving circuit for amplifying the signal in the frequency band A is used. When the circuit 12 is connected to the anode side terminal A of the photodiode 10 and the receiving circuit 16 for amplifying the signal of the frequency band B higher than the frequency band A is connected to the cathode side terminal K of the photodiode 10. Is the capacitance C ₂ that constitutes the bypass circuit.
May be connected to the anode side terminal A of the photodiode 10 as in the receiving circuit 12. Even in this case,
The same effect as in the case of the second embodiment can be obtained.

[0032]

As described in detail above, according to the band division type optical receiver of the present invention, the first receiving circuit for amplifying the electric signal corresponding to the optical signal of the first frequency band is the photodiode. A second receiving circuit connected to the first terminal of the photodiode and amplifying an electric signal corresponding to an optical signal in the second frequency band higher than the first frequency band is connected to the second terminal of the photodiode. A bypass circuit for releasing an electric signal having a frequency higher than a predetermined frequency to the ground potential is connected to the first terminal of the photodiode, so that the frequency is higher than the first frequency band input to the first receiving circuit. Can be released to the ground potential through the bypass circuit. Therefore, an electric signal having a frequency higher than the first frequency band input to the first receiving circuit appears at the input of the second receiving circuit via the capacitance Cj of the photodiode, and the input signal level of the second receiving circuit is increased. Will no longer decrease,
It is possible to prevent the deterioration of the output characteristics of the second receiving circuit that amplifies the signal in the high frequency band. Therefore, the output characteristics of the first receiving circuit and the second receiving circuit are almost equal to the output characteristics when the first receiving circuit and the second receiving circuit are individually connected to the photodiode.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a band division type optical receiver according to an embodiment of the present invention.

FIG. 2 is a graph showing a frequency-multiplexed optical signal input to the photodiode of the band-division type optical receiver of FIG.

FIG. 3 is a graph showing an electric signal output from an output terminal of the band division type optical receiver of FIG.

FIG. 4 is a circuit block diagram showing a band division type optical receiver having a bypass circuit according to the first embodiment.

FIG. 5 is a circuit block showing a band division type optical receiver having a bypass circuit according to a second embodiment.

6 is a graph showing output characteristics of the band division type optical receiver of FIG.

FIG. 7 is a block diagram showing a conventional band division type optical receiver.

8 (a) is a graph showing a frequency-multiplexed optical signal input to the band division type optical receiver of FIG. 7, and FIGS. 8 (b) and 8 (c) are graphs of FIG. It is a graph which shows the electric signal output from a band division type optical receiver.

9 is an equivalent circuit diagram of a photodiode of the band division type optical receiver of FIG.

10 is a graph showing deterioration of output characteristics of the band division type optical receiver of FIG.

[Explanation of symbols]

10 ... Photodiode, 12 ... Receiving circuit, 14 ... Output terminal, 16 ... Receiving circuit, 18 ... Output terminal, 20 ... Bypass circuit, 22 ... Current source, K ... Cathode side terminal, A ... Anode side terminal, C ₁ , C ₂ , C ₃ ... Capacitance, L ... Inductor, R ... Resistor.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location H04B 10/26 H04J 14/00 14/02

Claims (3)

[Claims] 1. A photodiode that receives an optical signal in a wide frequency band and converts it into an electrical signal; and a first optical signal that is connected to a first terminal of the photodiode and that is received by the photodiode. A first receiving circuit that amplifies an electrical signal corresponding to an optical signal in a frequency band and outputs the amplified signal to a first output terminal; and an optical signal that is connected to a second terminal of the photodiode and is received by the photodiode. A second of which amplifies an electric signal corresponding to an optical signal of a second frequency band higher than the first frequency band and outputs the amplified electric signal to a second output terminal.
And a bypass circuit which is connected to the first terminal of the photodiode and releases an electric signal having a frequency higher than a predetermined frequency to the ground potential. 2. The bypass circuit includes a first capacitor, an inductor, and a resistor that are connected in series, and a second capacitor that is connected in series to the first capacitor. The optical receiver according to claim 1, wherein one end is connected to the first terminal of the photodiode, and one end of the resistor and one end of the second capacitor are grounded. 3. The optical circuit according to claim 1, wherein the bypass circuit includes a capacitor, one end of the capacitor is connected to the first terminal of the photodiode and the other end is grounded. Receiver.