JPH11355218A - Optical burst cell signal reception circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical burst cell signal reception circuit which is highly sensitive and has a broad dynamic range. SOLUTION: An avalanche photodiode 1 as a photoelectric converter converts an inputted optical burst cell signal into a burst cell signal of an electric signal. An avalanche photodiode driving circuit 2 supplies the avalanche photodiode 1 with a bias voltage. A preamplifier 3 amplifies the burst cell signal from the avalanche photodiode 1. A level detection circuit 4 detects a voltage level of the amplified burst cell signal. An AGC circuit 5 which instantaneously responds and amplifies a voltage value of the burst signal to be inputted up to a specified voltage value. A discrimination/timing extraction IC 6 is composed of a discrimination circuit for discriminating whether a level of the signal is '1' or '0' and a timing extraction circuit for extracting a clock signal from the burst cell signal at high speed. A bypass circuit 7 is generated between terminals of the avalanche photodiode 1 and bypasses a charged and discharged current. A switch 8 connects an anode of the avalanche photodiode 1 to either the preamplifier 3 or the bypass circuit 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a passive double
The present invention relates to an optical burst cell signal receiving circuit for upstream signals of a star (PDS) optical network.

[0002]

2. Description of the Related Art FIG. 2 shows a configuration of a conventional optical burst cell signal receiving circuit. The optical burst cell signal receiving circuit shown in FIG. 6 includes a photoelectric conversion circuit 105, a preamplifier 106,
It comprises a GC (Auto Gain Control) circuit 107 and an identification / clock extraction circuit 108. Here, the input optical burst cell signals having different light levels are amplified to a certain level by the AGC circuit 107 which responds instantaneously at the same speed as the signal speed, and then are discriminated and reproduced by the discrimination / clock extraction circuit 108. .

[0003]

FIG. 7 is a schematic block diagram of an optical access network of the passive double star system.
(A). An optical transmission line L via a star coupler 101 is connected between the subscribers # 1 to #n (n is a natural number) and the station 100. For example, subscriber #
The upstream optical burst cell signals output from 1, the subscriber # 2 and the subscriber #n become signals arranged in time series as shown in FIG. 7B when input to the receiving circuit of the station 100.

The upstream signal receiving circuit installed in the station 100 converts an optical burst cell signal into a burst cell signal, which is an electric signal, and an amplifier that amplifies the converted burst cell signal to a predetermined level. A circuit, a clock extraction circuit for rapidly extracting a clock signal from the amplified burst cell signal, and a signal level of “1” or “1”.
And an identification circuit for identifying whether it is 0 ”.

Here, the optical burst cell signals output from the subscribers # 1 to #n are based on the distance between each of the subscribers # 1 to #n and the star cover 101 and the star coupler 101. By the loss according to the branching ratio, etc.
Generally, the optical level differs for each optical burst cell signal. Such an optical burst cell signal receiving circuit includes:
When the number of subscribers, that is, the number of branches increases, and when the distance between the subscriber # 1 to the subscriber #n and the station 100 increases, it is required to improve the reception sensitivity and expand the dynamic range.

In a receiving circuit using an avalanche photo diode (hereinafter referred to as APD) as a photoelectric conversion circuit, a large improvement in receiving sensitivity can be obtained.
However, for an optical burst cell signal having a large input signal, there has been a problem that the level of an electric signal input to the identification circuit becomes large and reception becomes difficult. For this reason, the situation where the dynamic range is reduced rather than the receiving circuit using the PIN-PD often occurs.

The present invention has been made under such a background, and has as its object to provide an optical burst cell signal receiving circuit having high sensitivity and a wide dynamic range.

[0008]

According to the first aspect of the present invention,
In the optical burst cell signal receiving circuit, a circuit for receiving an optical burst cell signal having a different light level,
Detecting means for detecting the light level of the optical burst cell signal, an avalanche photodiode, and an amplifier circuit for amplifying a signal photoelectrically converted by the avalanche photodiode to a voltage signal of a predetermined level, and An avalanche photodiode driving circuit for changing a multiplication factor of the avalanche photodiode within at least the first few bytes of the burst cell signal according to an optical level of the optical burst cell signal; and A bypass circuit for bypassing a current generated due to a change in multiplication factor, a first opening / closing means for opening / closing the bypass circuit, and a second opening / closing means disposed between the avalanche photodiode and the amplifier circuit And characterized in that:

According to a second aspect of the present invention, there is provided the optical burst cell signal receiving circuit according to the first aspect. The avalanche photodiode driving circuit changes the multiplication factor of the avalanche photodiode in a stepwise manner according to the light level of the optical burst cell signal input.

According to a third aspect of the present invention, in the optical burst cell signal receiving circuit according to the first or second aspect,
The driving circuit of the avalanche photodiode,
According to the magnitude of the input optical signal, the avalanche photo
It is characterized in that the multiplication factor of the diode is changed to two values.

According to a fourth aspect of the present invention, in the optical burst cell signal receiving circuit according to any one of the first to third aspects, a means for splitting an input optical signal and a photoelectric converter as an optical level detecting means are provided. The multiplication factor of the avalanche photodiode is changed by feedforward control.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a configuration of an optical burst cell signal receiving circuit according to one embodiment of the present invention. In this figure, reference numeral 1 denotes an avalanche photodiode as a photoelectric converter, which converts an input optical burst cell signal into a burst cell signal which is an electric signal.

An avalanche photodiode (APD) driving circuit 2 supplies a bias voltage to the avalanche photodiode 1. Further, the avalanche photodiode driving circuit 2 increases the multiplication factor for the burst cell having a small input signal level because the multiplication factor of the avalanche photodiode 1 changes according to the change of the bias voltage. On the other hand, for a signal having a large input signal level, the set value of the bias voltage is changed for each burst cell so as to reduce the multiplication factor.

Therefore, the avalanche photodiode driving circuit 2 reduces the difference between the voltage levels of the burst cell signals output from the avalanche photodiode 1 and reduces the dynamic level of the avalanche photodiode 1 as a receiving circuit. Expand the range. The avalanche photo diode driving circuit 2
The adjustment of the bias voltage for the change in the multiplication factor is completed in a time within several bits of the burst cell signal. Here, the adjusted amplification factor of the avalanche photodiode 1 is maintained at a constant value during the input of at least one burst cell signal.

Reference numeral 3 denotes a preamplifier, which amplifies a burst cell signal from the avalanche photodiode 1. A level detection circuit 4 detects the voltage level of the amplified burst cell signal, that is, the light level of the input optical burst cell signal. 5 is an AG that responds instantly
The C circuit amplifies the voltage value of the input burst signal to a constant voltage value.

The avalanche photodiode driving circuit 2 and the AGC circuit 5 perform a reset operation at a guard time between burst cell signals, and wait for a burst cell signal to follow. 6 is identification / timing extraction I
C, which comprises an identification circuit for identifying whether the signal level is "1" or "0", and a timing extraction circuit for extracting a clock signal from a burst cell signal at high speed.

Reference numeral 7 denotes a bypass circuit, which is an avalanche circuit.
Generated between the terminals of the photodiode 1 and the AGC circuit 5
Bypass the charging / discharging current that causes malfunction of the device. The charging / discharging current between the terminals of the avalanche photodiode 1 is generated when the multiplication factor of the avalanche photodiode 1, that is, when the bias voltage is switched according to the signal level of the input optical burst cell signal.

8 is an avalanche photodiode 1
And a switch provided between the preamplifier 3 and the bypass circuit 5, and connects the anode of the avalanche photodiode 1 to one of the input terminal of the preamplifier 3 and the input terminal of the bypass circuit 7. . The switch 8 includes a switch A and a switch B. For example, according to a timing chart shown in FIG.
The connection between the anode of the avalanche photodiode 1 and either the input terminal of the preamplifier 3 or the input terminal of the bypass circuit 5 is switched by the switches A and B.

Next, an example of the operation of the embodiment will be described with reference to FIGS. FIG. 3 is a diagram illustrating the relationship between the input optical signal level and the multiplication factor of the avalanche photodiode 1 for explaining the operation of the avalanche photodiode 1 according to the embodiment. For example, assume that the optical level of the input burst cell signal has changed to a high level. At this time, that is, at a time before the time t1, the switch B of the switch 8 is "ON",
Switch A is "off".

The avalanche photodiode 1
The input optical burst cell signal is converted into a burst cell signal and output to the preamplifier 3. And preamplifier 3
Amplifies the input burst cell signal at a predetermined amplification factor, and outputs the amplified burst cell signal to the level detection circuit 4. As a result, the detection circuit 4 detects that the optical level of the optical burst cell signal has increased, and outputs the detection signal including the level data to the avalanche photodiode driving circuit 2.

Next, the avalanche photodiode driving circuit 2 adjusts the bias voltage applied to the avalanche photodiode 1. Then, the avalanche photodiode driving circuit 2 outputs a control signal to the switch 8 to turn off the switch B at time t1 and turn on the switch A at time t2. Thereby, the charging / discharging current generated between the terminals of the avalanche photodiode 1 during the adjustment of the bias voltage can be prevented from leaking into the preamplifier 3.

As a result, the anode of the avalanche photodiode 1 is disconnected from the input terminal of the preamplifier 3 and connected to the input terminal of the bypass circuit 7. Then, at time t3, the avalanche photodiode driving circuit 2 determines the input optical signal level and the avalanche photomultiplier shown in FIG.
The bias voltage applied to the avalanche photodiode 1 is set to “H” based on the relationship with the multiplication factor of the diode 1.
Adjust "L" level from level.

The charging / discharging current generated between the terminals of the avalanche photodiode 1 at the time t3 is adjusted flows to the bypass circuit 7. Then, at time t4 after a lapse of time sufficient for the charging / discharging current to finish flowing, the avalanche photodiode drive circuit 2 turns off the switch A and turns on the switch B. This allows
The multiplication factor of the avalanche photodiode 1 becomes a value corresponding to the light level of the optical burst cell signal input, and the burst cell signal input to the AGC circuit 5 has a voltage value within a predetermined voltage level range.

The bias voltage usually reaches several tens of volts, and the voltage amplitude required to change the multiplication factor is several volts to one volt.
It reaches 0V. Therefore, based on the relationship between the continuous input optical signal level and the multiplication factor of the avalanche photodiode 1 shown in FIG. 3A, the multiplication factor changes at high speed in accordance with the input optical signal level. It will be difficult to make it happen.

Therefore, as shown in FIGS. 3 (b) and 3 (c), a method of switching the multiplication factor of the avalanche photodiode 1 step by step becomes effective. In this case, a large change occurs in the output signal level of the avalanche photodiode 1 at the light input level near the switching boundary, but it can be covered by the dynamic range of the AGC circuit 5 provided at the subsequent stage as shown in FIG. it can.

Here, the relationship between the input optical signal level and the multiplication factor of the avalanche photodiode 1 shown in FIG. 3B changes stepwise, and the input optical signal level is a predetermined value. , And the value of the multiplication factor of the avalanche photodiode 1 corresponding to each of the ranges is given. In addition, the relationship between the input optical signal level and the multiplication factor of the avalanche photodiode 1 shown in FIG.
-th "is set. If the value is equal to or less than the threshold value, the multiplication factor of the avalanche photodiode 1 is set to" M2 ".
Is "M1".

As described above, one embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and a design change or the like may be made without departing from the gist of the present invention. The present invention is also included in the present invention. For example, as a second embodiment, it is also possible to measure the optical level of an input optical burst cell signal by using the photoelectric conversion means 10 shown in FIG. 5 instead of the level detection circuit 4 of the first embodiment. It is. The avalanche photodiode driving circuit 2 'differs from that of the one embodiment in that a level determining function is operatively added internally.

A detection method using the photoelectric converter 10 will be described. The photoelectric conversion means 10 branches a part of the input optical burst cell signal by the coupler 11 and converts the part of the optical signal into an avalanche photodiode driving circuit 2 '.
Output to The avalanche photodiode driving circuit 2 ′ has a relationship between the optical level of the input optical signal and the input optical signal level stored therein and the multiplication factor of the avalanche photodiode 1 shown in FIG. The multiplication factor is changed by the feed forward control based on. The detection method described above is directly applied to avalanche photo
Since the diode drive circuit 2 ′ determines the light level,
This is effective in improving the switching speed of the multiplication factor.

Here, as the photoelectric converter 10, a PIN
A photodiode, an avalanche photodiode, or the like is applicable. An optical coupler or the like can be used as the coupler 11 for branching the input signal.

As described above, according to the present invention, the multiplication factor of the avalanche photodiode 1 is increased in order to solve the problem that the dynamic range is reduced, which is a problem in the conventional burst signal receiving circuit using the avalanche photodiode. By instantaneously changing the optical burst cell signal according to the input level of the input optical burst cell signal, it is possible to realize an optical burst cell signal receiving circuit having high sensitivity and a wide dynamic range.

[0031]

According to the optical burst signal receiving circuit of the present invention, even when the level of the input optical burst cell signal changes for each optical burst cell, the level of the input optical burst cell signal is reduced. By changing the multiplication factor of the avalanche photodiode accordingly, there is an effect that high sensitivity and a wide dynamic range can be simultaneously realized.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an optical burst cell signal receiving circuit according to an embodiment of the present invention.

FIG. 2 is a timing chart showing an operation of the switch 8 shown in FIG.

FIG. 3 is a diagram showing a relationship between an input optical signal level and a multiplication factor of the avalanche photodiode 1 shown in FIG.

FIG. 4 is a diagram showing a dynamic range of the AGC circuit 5 shown in FIG.

FIG. 5 is a block diagram showing a configuration of an optical burst cell signal receiving circuit according to a second embodiment of the present invention.

FIG. 6 is a block diagram showing a configuration of a conventional optical burst cell signal receiving circuit.

FIG. 7 is a schematic configuration diagram of a passive double star type optical access network.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 avalanche photo diode 2 avalanche photo diode (APD) drive circuit 3 preamplifier 4 level detection circuit 5 AGC circuit 6 identification / timing extraction IC 7 bypass circuit 8 switcher A, B switch

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI H03F 3/08 (72) Inventor Atsushi Kusaka 20-1 Sakuragaoka-cho, Shibuya-ku, Tokyo Inside NTT Electronics Corporation (72) Invention Person Takanori Fujisawa 20-1 Sakuragaoka-cho, Shibuya-ku, Tokyo Inside NTT Electronics Corporation

Claims (4)

[Claims] 1. A circuit for receiving optical burst cell signals having different optical levels, comprising: detecting means for detecting the optical level of the optical burst cell signal; an avalanche photodiode; and the avalanche photodiode. An amplification circuit for amplifying the signal photoelectrically converted by the amplifying circuit into a voltage signal of a predetermined level; and a multiplication factor of the avalanche photodiode according to an optical level of the input optical burst cell signal. An avalanche photodiode driving circuit that changes within a few bytes, a bypass circuit that bypasses a current generated due to a change in a multiplication factor of the avalanche photodiode, and a first opening / closing unit that opens and closes the bypass circuit. Between the avalanche photodiode and the amplifier circuit Optical burst cell signal receiving circuit characterized by comprising comprises a second switching means which is location. 2. The avalanche photodiode driving circuit changes a multiplication factor of an avalanche photodiode stepwise according to an optical level of the optical burst cell signal inputted. 2. The optical burst cell signal receiving circuit according to 1. 3. The avalanche photodiode driving circuit changes a multiplication factor of the avalanche photodiode into a binary value according to the magnitude of an input optical signal. 3. The optical burst cell signal receiving circuit according to 2. 4. An avalanche photomultiplier according to claim 1, further comprising means for splitting an input optical signal as means for detecting an optical level, and a photoelectric converter.
4. The optical burst cell signal receiving circuit according to claim 1, wherein the multiplication factor of the diode is changed.