JPH06318908A - Burst signal detecting circuit - Google Patents

Abstract

PURPOSE:To detect the arrival of a burst signal with a different amplitude for each ONU(optical network unit) provided with a DC component in the burst multiplex transmission system of a PDS(passive double star) system in a short time. CONSTITUTION:An NRZ burst signal (a) outputted from an optical receiver 1 is turned to a signal (b) by performing DC cut-off at a capacitor 2. By providing a phase circuit 3 to apply phase transition to the signal (b) and calculating difference between the signal (b) and a phaser output signal (c) by using a differential amplifier 4, a bipolar signal (d) canceled the DC component is provided. A counter circuit 8 is operated by the bipolar signal (a) and after the prescribed number of pulses are counted, a burst detect signal (k) is outputted.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a PDS (Passive Doub)
The present invention relates to a receiving circuit in a burst multiplex transmission system such as a le Star) system, and particularly to a burst signal detecting circuit for detecting arrival of a burst signal.

[0002]

2. Description of the Related Art The PDS transmission system shown in FIG. 3 is one system that constitutes an optical subscriber system, and is an SLT (Subs)
O installed from the criber line terminal)
A multiplexing node such as a star coupler is provided on the way to the NU (Optical Network Unit) to connect a plurality of ONUs and SLTs. A plurality of ONUs share the same optical fiber between the SLT and the multiplexing node. As shown in FIG. 3, the signal from the SLT to the ONU is transmitted in a broadcast form as a time division multiplexed signal.

On the other hand, a burst signal is transmitted from the ONU to the SLT, and at the SLT receiving point, the burst signals from a plurality of ONUs are aligned so as not to overlap each other. Therefore, the ONU controls and transmits its own burst transmission timing so as not to collide with burst signals from other ONUs at the SLT reception point. Further, a preamble as shown in FIG. 4 is added to the signal from the ONU to the SLT to identify the start position of the burst, and in addition to controlling the burst transmission timing, a guard time is provided in order to prevent collision of each burst. Has been. Since the PDS transmission method is a transmission method using light, signal transmission from the ONU and SLT is performed using a light emitting element such as an LD (Laser Diode). A scrambled NRZ code is used as the transmission code from the viewpoint of transmission efficiency.

On the other hand, on the receiving side (SLT), PD (Photo
A light receiving element such as a diode) performs optical / electrical conversion to obtain an electric signal, and an amplifier amplifies it to a level required for subsequent processing. At present, between the optical element and the amplifier, there is no choice but to couple them with a capacitor, because the DC drift of the light receiving element is large, and if they are directly connected, the operating point of the amplifier exceeds the allowable range. Therefore, the zero potential point of the amplifier output waveform varies depending on the number of multiplexed burst signals and the amplitude.

[0005]

The received waveform at the SLT is as shown in FIG. 4, where the A section shows the case where the distance to the ONU is short, and the B section shows the case where the distance to the ONU is long. To receive this signal waveform and detect the beginning of the burst,
It is necessary to detect the average DC component of each burst from the DC blocked unipolar burst signal (FIG. 4) and convert it to a received burst signal and convert it to a bipolar burst signal.

The reason is that the difference between the amplitudes of the burst signals is 30 dB to 40 dB depending on the distance to the ONU, and if it is attempted to process the unipolar signal with the DC cut off, the dynamic range of the amplifier used must be extremely widened. I won't. For example, if the minimum level signal is amplified to 1V, the maximum level signal becomes 30 to 100V, and 30 to 100V is also required as the saturation point of the amplifier. If saturation occurs in the amplifier, the minimum level signal disappears with a limiter applied (Fig. 5).
(A)). On the other hand, if it can be converted into a bipolar signal, it is sufficient that the minimum level signal can be output as the saturation point of the amplifier. The signal of maximum level is naturally subject to large amplitude limitation, but the information near the zero crossing of the waveform is not lost, so
There is no problem in detecting a burst signal (FIG. 5 (b)).

Next, in the PDS method, the end position and the start position of the burst are usually fixed at predetermined positions on the time slot. However, when the ONU is installed, a "burst for measurement" having a short burst length is set prior to full-scale operation. O
It is sent from the NU and the transmission line delay time is measured. In this case, it is uncertain at which position on the time slot the "measurement burst" appears, and the burst start position must be detected by some method. It is necessary that the detector does not erroneously detect due to line noise. The present invention has been made in view of such circumstances, and it is an object of the present invention to provide a burst signal detection circuit that detects arrival of burst signals including a DC component and having different amplitudes for each ONU in a short time. It is an issue.

[0008]

In order to solve the above-mentioned problems, in a burst signal detection circuit of the present invention, a phase circuit for giving a predetermined phase transition to a received signal is provided, and a received signal is generated by a differential amplifier. By taking the difference between the phaser output signals, a bipolar signal in which the DC component is canceled is obtained. The bipolar circuit operates the counter circuit to output a burst detection signal after counting a predetermined number of pulses.

[0009]

According to the burst signal detecting circuit constructed as described above, the head of the burst signal can be detected reliably and in a short time.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. (First Embodiment) FIG. 1 (a) is a block diagram, FIG. 1 (b).
Shows the time chart. The NRZ burst signal a, which is the output of the optical receiver 1, is DC blocked by the capacitor 2,
It becomes the signal b. The signal b is input to the phase circuit 3, and a signal c whose phase has shifted by a predetermined amount is obtained from the output. The differential amplifier 4 receives the signal b and the signal c at its inputs, and the burst signal d in which the DC component is canceled is taken out from the output. The counter circuit 8 operates by using the signal d as a count input, and sets the output signal k from the counter circuit 8 to a high level when the counting of a predetermined number is completed. FIG. 1B shows an example in which four positive pulse pulses of the signal d are counted and detected. The counter circuit 8 is reset by the burst signal end signal detected by another means (not shown).

(Second Embodiment) FIG. 2A shows a block diagram and FIG. 2B shows a time chart thereof. The NRZ burst signal a, which is the output of the optical receiver 1, is blocked by the capacitor 2 for direct current and becomes a signal b. The signal b is input to the phase circuit 3, and a signal c whose phase has shifted by a predetermined amount is obtained from the output. The differential amplifier 4 receives the signal b and the signal c at its inputs, and extracts the bipolar signals d and e from which the DC components have been canceled out. The signal d is a positive phase output, and the signal e is a negative phase output. The signal d is connected to the positive phase input of the first comparator 5 and the negative phase input of the second comparator 6, and the signal e is the negative phase input of the first comparator 5 and the positive phase input of the second comparator 6. Connected to phase input.

As a result, the signal f which identifies the positive polarity pulse in the signal d appears at the output of the first comparator 5, and the second
At the output of the comparator 6, the signal g that identifies the negative polarity pulse in the signal d appears. The signal g and the signal f are respectively input to the OR circuit 7, and the double frequency signal h obtained by combining the signals g and f is taken out from the output thereof. Counter circuit 8
Operates with the double frequency signal h as a count input, and sets the output signal k from the counter circuit 8 to a high level when the counting of a predetermined number is completed. In FIG. 2B, the double frequency signal h
An example is shown in which the detection is performed by counting the four pulses of. Therefore, the second embodiment can detect the arrival of the burst signal in a shorter time than the first embodiment.

[0013]

As described above, in the burst signal detecting circuit of the present invention, the phase circuit 3 for phase shifting the received signal is used.
A differential amplifier 4 which receives the output and the received signal and outputs a pulse in which the DC component is canceled, and a counter 5 which counts the output pulse by a predetermined number. Therefore, the arrival of the burst signal can be detected in an extremely short time.

[Brief description of drawings]

FIG. 1A is a block diagram showing a first embodiment of the present invention, and FIG. 1B is a time chart of each point.

FIG. 2A is a block diagram showing a second embodiment of the present invention, and FIG. 2B is a time chart of each point.

FIG. 3 is a configuration diagram showing an outline of a PDS system.

FIG. 4 is a waveform diagram of a received burst signal output from a PDS optical receiver.

5A shows an operation example in which a unipolar burst signal is amplified, and FIG. 5B shows an operation example in which a bipolar burst signal is amplified.

[Explanation of symbols]

 Three-phase circuit. 4 Differential amplifier. 8 counters.

Claims (1)

[Claims] 1. A phase circuit (3) for giving a phase shift to a received signal, and a differential circuit which receives the output of the phase circuit and the received signal at each input terminal and outputs a signal in which a DC component is canceled. A burst signal detection circuit comprising an amplifier (4) and a counter (8) which receives the differential amplifier output, counts a predetermined number of pulses, and generates a burst signal detection output.