JPH1032543A - Optical receiving circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce manufacturing cost and to reduce noise by providing a high-pass filter in one of the anode and the cathode of a photodiode and a low-ass filter in the other thereby and simultaneously extracting high/low frequency signals thereby unnecessitating a preamplifier, etc., even at the time of transmitting light while superimposing the low frequency signal on the high frequency signal. SOLUTION: A filter circuit consists of the low-pass filter 5 connected to one of the anode side and the cathode side of the photodiode 1 and a low-pass filter 4 connected to the other of the anode side and the cathode side. Then the filter circuit extracts electric signals of different frequencies The anode side of the photodiode 1 is grounded through a load impedance 2 and the cathode side is connected to an inverse bias power source VB through a load impedance 3. The photodiode 1 is irradiated with the light obtained by analog-optical- modulating high/low frequency electrical signals altogether and a backward current according to illuminance flows through the photodiode 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical receiving circuit used for optical communication of a frequency multiplexing transmission system, and more particularly, to light for extracting signals having different frequency bands from an anode side and a cathode side of a photodiode as a light receiving element. It relates to a receiving circuit.

[0002]

2. Description of the Related Art In subcarrier multiplexed analog optical transmission, a plurality of high-frequency electrical signals having different frequencies modulated by a plurality of baseband signals are respectively subjected to analog optical modulation on a light-emitting element using a frequency-multiplexed high-frequency signal.
The generated analog optical signal is transmitted by optical fiber,
The transmitted optical signal is converted into an electric signal by an optical receiving circuit. Such subcarrier multiplexed analog optical transmission is a transmission system that utilizes the characteristics of a wideband, low-loss, non-guided, low-crosstalk, light-weight, small-diameter, and flexible optical fiber. It is used for batch transmission of multichannel high-frequency signals and transmission of high-frequency signals between a base station and an antenna for mobile communication.

[0003] For example, in CATV, a multi-channel video signal is modulated with carrier waves having different frequencies, respectively, and a frequency of approximately 6 MHz is set between 50 MHz and 500 MHz.
In mobile / mobile phones for mobile communication, analog and digital signals are assigned to the 800 MHz band, and digital signals are assigned to the 1.5 GHz band. In these analog optical transmissions, the above-mentioned frequency signals are collectively subjected to analog optical modulation and transmitted using the broadband characteristics of the frequency response of a semiconductor laser as a light source.

[0004] In the above-mentioned mobile communication and the like, due to the system configuration, in addition to the above-mentioned signals, a control / monitoring signal may be superimposed and transmitted for state control and monitoring of the receiving device at the transmission destination. is there. For example, in a relay amplifying device for countermeasures against blind spots of a mobile phone, the control / monitoring signal is 1200 bp.
Since a transmission speed of about s is sufficient, the control signal is subjected to modulation operation such as frequency shift keying (FREQENCY SHIFT KEYING) to perform frequency conversion to a lower band sufficiently separated from the transmission band of the high-frequency multiplexed signal. In this case, a signal is input to the light emitting element at the same time, or is superimposed as an electric signal in the audio band, and analog optical modulation is performed by using a modem in the audio band and transmitted. An optical receiving circuit that receives a control / monitoring signal together with the above-described high-frequency multiplexed signal is provided with a wide-band preamplifier.

[0005]

However, in the above-described optical receiving circuit, a wideband preamplifier is required, which causes an increase in manufacturing cost and a problem that noise is easily generated. Was. The present invention has been made in view of the above problems, and has as its object to provide an optical receiving circuit that does not require a preamplifier, can be manufactured at low cost, and can suppress generation of noise.

[0006]

SUMMARY OF THE INVENTION To achieve the above object, the present invention relates to an optical receiving circuit for receiving an optical signal obtained by analogly modulating a plurality of electric signals having different frequencies into a photodiode and converting the signal into an electric signal. A filter circuit is provided on each of the anode side and the cathode side of the photodiode to extract electric signals having different frequencies.

The optical signal is an optical signal obtained by subjecting a high-frequency electric signal and a low-frequency electric signal to analog optical modulation at the same time, and the high-frequency electric signal is the above-mentioned high-frequency multiplexed signal (main transmission signal).
In addition, the low frequency electric signal is represented by a control / monitoring signal. More specifically, in a case where the present invention is applied to mobile communication, the high-frequency electric signal is a radio high-frequency signal, and the low-frequency signal is a voice band signal having a maximum frequency of about 3 kHz.

The filter circuit includes a low-pass filter connected to one of the anode and the cathode of the photodiode, and a high-pass filter connected to the other of the anode and the cathode. More specifically, this filter circuit is a combination of a well-known coil L and a capacitor C, that is, a coil that extracts a high-frequency electric signal through a capacitor C connected in series and a coil that connects a low-frequency output in series. It is configured to retrieve through L.

In the light receiving circuit according to the present invention, a signal whose phase is inverted is simultaneously generated on the anode side and the cathode side of the photodiode, and a high frequency signal is output from one of the anode and the cathode, and a low frequency signal is output from the other. It is taken out through. For this reason, it is not necessary to provide a preamplifier, so that the device can be manufactured at low cost. In addition, since no preamplifier is provided, the risk of generating noise is reduced.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing an optical receiving circuit according to one embodiment of the present invention. Note that this embodiment is applied to the above-described relay amplifying apparatus for countermeasures against blind spots in mobile communication, but the description of the peripheral configuration is omitted.

In FIG. 1, reference numeral 1 denotes a photodiode, and the photodiode 1 has a load impedance 2 on the anode side.
And the cathode side has a load impedance of 3
It is connected to the backward bias power source V _B via. The photodiode 1 is irradiated with light W (optical signal) obtained by subjecting the high-frequency electric signal and the low-frequency electric signal to analog light modulation collectively, and a reverse current according to the illuminance of the optical signal W flows.

The photodiode 1 has an anode connected to a high-pass filter 4 in parallel with the load impedance 2, and a cathode connected to a low-pass filter 5 in parallel with the load impedance 3. The high-pass filter 4 is
It is connected to a signal amplifier (terminal a in the figure) not shown through the high frequency amplifier 6. The high-pass filter 4 has the aforementioned 80
A high frequency signal in the 0 MHz band or 1.5 GHz band is selectively output to the high frequency amplifier 6. The high frequency amplifier 6 has 8
A signal having characteristics suitable for amplifying a high-frequency signal in a 00 MHz band or a 1.5 GHz band is used, and an output signal of the high-pass filter 4 is amplified and output to a terminal a.

The low-pass filter 5 is connected to a relay controller (terminal b in the figure) (not shown) via a low-frequency amplifier 7. The low-pass filter 5 selectively outputs the above-mentioned low frequency signal of about 1200 Hz to the low frequency amplifier 7 from the signal generated at the cathode of the photodiode 1. The low-frequency amplifier 7 is suitable for amplifying a low-frequency signal of about 1200 Hz. The low-frequency amplifier 7 amplifies the output signal of the low-pass filter 5 and outputs it to the terminal b.

In this embodiment, an optical signal W is applied to the photodiode 1 via an optical cable, and a reverse current corresponding to the illuminance of the optical signal W flows through the photodiode 1, and the inside of the photodiode 1 Due to the resistance, signals having different phases are generated at the anode and the cathode, respectively. A main transmission signal, which is a high-frequency signal, is taken out from the anode side of the photodiode 1 by the high-pass filter 4 and amplified by the amplifier 6 and input to the relay amplifier a. Is taken out, amplified by the amplifier 7, and input to the relay controller b.

That is, the optical receiving circuit according to this embodiment can take out the high-frequency main transmission signal and the low-frequency control / monitoring signal from the anode side and the cathode side of the photodiode 1 at the same time. Do not need. For this reason, generation of noise can be suppressed, the circuit configuration can be simplified, and the manufacturing cost can be reduced.

In this embodiment, the main transmission signal, which is a high-frequency signal, is taken out from the anode side of the photodiode 1 and the control / monitoring signal, which is a low-frequency signal, is taken out from the cathode side. A control / monitoring signal may be provided by providing a filter, and a main transmission signal may be provided by providing a high-pass filter on the cathode side.

FIG. 2 is a circuit diagram of an optical receiving circuit according to another embodiment of the present invention. The same parts as those of the optical receiving circuit according to the embodiment of FIG. 1 described above are denoted by the same reference numerals, and description thereof is omitted.

This embodiment shows a case where the control / monitoring signal is a signal modulated by a voice band modem, for example, a 1300 Hz and 2400 Hz FSK signal. As shown in the figure, the cathode of the photodiode 1 is connected to the backward bias power source V _B via a high frequency choke coil L1, the reverse bias power supply V _B terminal of the high-frequency choke coil L1 is grounded via a bypass capacitor C1 You. Then, the high-frequency amplifier 6 is connected to the cathode of the photodiode 1 via the coupling capacitor C3, and the terminal of the coupling capacitor C3 on the high-frequency amplifier 6 side is grounded via the load resistor R1, and is connected to the high-frequency amplifier 6. You.

The high-frequency choke coil L1 has a sufficiently high impedance for a high-frequency main transmission signal, a sufficiently low impedance for a low-frequency voice band signal, and an inductance of about 1 uH. Bias capacitor C1
Is for avoiding noise mixed in from a reverse bias power supply. The coupling capacitor C3 has a sufficiently low impedance for the main transmission signal and a sufficiently high impedance for the voice band signal, and has a capacitance of about 10 to 100 pF. The load resistor R1 is used as a load resistor for a high-frequency signal that is a main transmission signal.

The anode of the photodiode 1 is connected to a capacitor C2 and a choke coil L connected in series.
2 is grounded via a load resistor R2, and a low frequency amplifier 7 is connected between the high frequency choke coil L2 and the load resistor R2 via a coupling capacitor C4. The capacitor C2 is for grounding a high-frequency signal generated on the anode side, and has the same capacitance as the coupling capacitor C3 described above. The high-frequency choke coil L2 is high with respect to the main transmission signal, like the high-frequency choke coil L1 described above.
What has low impedance with respect to a voice band signal and an inductance of about 1 pH is used. The load resistance R2 is a load resistance for a voice band signal, and
The coupling capacitor C4 allows a voice band signal to pass therethrough and has a capacitance of about 1 to 100 uF.

In this embodiment, a high-frequency choke coil L1, a coupling capacitor C3 and a load resistor R1
Functions as a high-pass filter, and the capacitor C
2. The high-frequency choke coil L2, the load resistor R2, and the coupling capacitor C4 function as a low-pass filter.
Therefore, as in the above-described embodiment, the main transmission signal, which is a high-frequency signal, and the low-frequency control / monitoring signal can be simultaneously extracted from the cathode side of the photodiode 1.

[0022]

As described above, according to the optical receiving circuit of the present invention, a high-pass filter is provided on one of the anode and the cathode of the photodiode, and a low-pass filter is provided on the other, so that high-frequency signals and low-frequency signals can be simultaneously transmitted. Therefore, a preamplifier or the like is not required even when a low-frequency signal is superimposed on a high-frequency signal for optical transmission, so that manufacturing cost is reduced and noise can be reduced.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an optical receiving circuit according to an embodiment of the present invention.

FIG. 2 is a circuit diagram of an optical receiving circuit according to another embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 1 photodiode 2 load impedance 3 load impedance 4 high-pass filter 5 low-pass filter 6 high-frequency amplifier 7 low-frequency amplifier C1 capacitor C2 capacitor C3 capacitor C4 capacitor L1 choke coil L2 choke coil R1 resistance R2 resistance R3 resistance R4 resistance W optical signal

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location H04B 10/26 10/14 10/04 10/06

Claims (1)

[Claims] 1. An optical receiving circuit for receiving an optical signal obtained by subjecting a plurality of electric signals having different frequencies to analog light modulation to a photodiode and converting the signal into an electric signal, wherein filter circuits are respectively provided on an anode side and a cathode side of the photodiode. An optical receiving circuit provided to extract electric signals having different frequencies.