JPH0345046A - Optical communication system - Google Patents

Abstract

PURPOSE:To receive an NRZ data while a bit error rate and a pulse width distortion are minimized by controlling a threshold voltage of an optical reception circuit when an initializing signal whose mark rate is 1/2 is received and keeping the set threshold voltage when a signal other than the initializing signal is received. CONSTITUTION:The system consists of an optical transmission circuit 1 receiving a binary NRZ signal from an NRZ(non return zero) data input terminal 8 and receiving a switching signal from a switching signal input terminal 7, an optical reception circuit 3 connecting to an output of the optical transmission circuit 1 and an NRZ data output terminal 14 connecting to the output of the optical reception circuit 3. Then the binary NRZ data and an initializing signal whose mark rate is 1/2 are selected and sent and when the initializing signal is received, the threshold voltage is adjusted so as to minimize the bit error rate and the pulse width distortion corresponding to the reception signal level. When a signal other than the initializing signal is received, the set threshold voltage is kept even when the signal is changed. Thus, the dispersion in the transmission loss is large and the NRZ data including the DC component is received while the bit error rate and the pulse width distortion are minimized.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention is applied to optical transmission. The present invention is a binary NRZ (No.
The present invention relates to an optical communication system for transmitting n Return to Zero (non-zero return) data.

〔overview〕

In an optical communication system in which an optical transmission circuit and an optical reception circuit are connected via an optical transmission line, the present invention controls the dark value voltage of the optical reception circuit when an initialization signal with a mark rate of 1/2 is received. By holding the set threshold voltage without performing any control when a signal other than the initialization signal is received, the bit error rate and pulse width distortion are minimized for NRZ data that has large variations in transmission loss and contains DC components. It is designed so that it can be received in the following state.

[Conventional technology]

Binary NRZ data contains DC components due to continuous data “1” level or continuous data “0” level, so AC coupling cannot be used in the transmitting circuit and receiving circuit, so DC coupling is used. need to use it.

Conventionally, an optical transmission circuit for binary NRZ data consists of an optical transmitting circuit that converts the electrical signal of the binary NRZ data into an optical signal, and an optical receiving circuit that converts the received optical signal into an electrical signal. was composed of a PIN photodiode, an amplifier circuit, and a voltage comparison circuit with a fixed threshold voltage.

[Problem that the invention seeks to solve]

The conventional NRZ data optical concealed transmission circuit described above is
Since the threshold voltage of the voltage comparison circuit that discriminates between "0" and "1" is fixed, the bit error rate deteriorates as the received signal level increases and the distortion of the output pulse width increases.

The present invention aims to eliminate such drawbacks, and provides a method that can transmit NRZ data that has large variations in transmission loss and includes DC components while minimizing bit error rate and pulse width distortion. shall be.

[Means for solving problems]

The present invention includes an optical transmission circuit, an optical transmission line for transmitting a transmission signal of the optical transmission circuit, and an optical reception circuit for receiving the optical signal from the optical transmission line, and transmits NRZ data on the optical transmission line. In the optical communication system, an initialization signal generation circuit that generates an initialization signal with a mark rate of 1/2, binary NRZ data to be input, and the initialization signal are selected in the optical transmission circuit. and a selection circuit for transmitting data to the optical transmission line, and when the optical receiving circuit receives the initialization signal, the dark value voltage is set so that the bit error rate and pulse width distortion are minimized in accordance with the received signal level. The present invention is characterized by comprising a dark value control circuit that adjusts the voltage and, when a signal other than the initialization signal is received, holds the threshold voltage set by the initialization signal and supplies it to a voltage comparison circuit that discriminates the signal.

[Effect]

Binary NRZ data and an initialization signal with a mark rate of 1/2 are selected and transmitted, and when the initialization signal is received, the bit error rate and pulse width distortion are minimized in accordance with the received signal level. Adjust the threshold voltage to . As a result, the dark value voltage of the voltage comparison circuit that performs reception determination is set correctly. When a signal other than the initialization signal is received, the set threshold voltage is maintained even if the signal changes.

Thereby, NRZ data with large variations in transmission loss and including DC components can be received in a state where the bit error rate and pulse width distortion are minimized.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings. The figure is a block diagram showing the configuration of an embodiment of the present invention.

In the embodiment of the present invention, the binary NR data is input from the NRZ data input terminal 8.
An optical transmitting circuit 1 which manually inputs a Z signal and a switching signal from a switching signal input terminal 7, an optical receiving circuit 3 connected to the output of this optical transmitting circuit 1 via an optical transmission line 2, and this optical receiving circuit. and an NRZ data output terminal 14 connected to the output of the circuit 3.

The optical transmission circuit 1 includes an initialization signal generation circuit 6 and a selection circuit for manually inputting NRZ data from an NRZ data input terminal 8, an output signal from the initialization signal generation circuit 6, and a switching signal from a switching signal input terminal 7. It includes a circuit 4 and an electrical/optical conversion circuit 5 that manually inputs the output signal of the selection circuit 4 and outputs it to the optical transmission line 2.

The optical receiving circuit 3 also includes an optical/electrical conversion circuit IO that inputs the output signal of the optical transmission line 2, an initialization signal detection circuit 13 that inputs the output signal of the optical/electrical conversion circuit 10, and an optical/electrical conversion circuit 10 that inputs the output signal of the optical/electrical conversion circuit 10. A threshold control circuit 12 which manually inputs the output signal of the conversion circuit 10 and the output signal of the initialization signal detection circuit 13 inputs the output signal of the optical/electrical conversion circuit 10 and the output signal of the threshold control circuit 12 and outputs NRZ data. and a voltage comparison circuit 11 that outputs to a terminal 14.

Next, the operation of the embodiment of the present invention configured as described above will be described; the initialization signal generation circuit 6 generates an initialization signal with a mark rate of 1/2. Here, the simplest data “0” and “1”
” is considered to be an initialization signal. The selection circuit 4 selects either the NRZ data or the initialization signal using the switching signal, and the electrical/optical conversion circuit 5 selects either the NRZ data or the initialization signal.
Output to.

The electric/optical conversion circuit 5 inputs a light emitting element (for example, a light emitting diode or a laser diode) to ○N or ○FFL in response to a binary electric signal, and inputs an optical signal to the optical transmission line 2.

The optical signal propagated through the optical transmission line 2 is transferred to the optical-to-electrical conversion circuit 1
Enter 0. The optical/electrical conversion circuit 10 converts an optical signal into a current using a PIN photodiode or an avalanche photodiode, further performs current/voltage conversion, and a voltage comparison circuit 11 amplifies the voltage to a comparable level.

The initialization signal detection circuit 13 identifies whether the received signal is an initialization signal or other signals, and outputs a signal that activates the threshold control circuit 12 only when the initialization signal is received. When the threshold control circuit 12 is activated by the initialization signal detection circuit 13, the threshold voltage of the voltage comparison circuit 11 is adjusted to an optimal value in accordance with the output signal level of the optical/electrical conversion circuit 10.

The optimum value is the value at which the bit error rate of the NRZ output data of the optical receiving circuit 3 is minimized and the pulse width distortion is minimized.

Due to variations in the optical output level of the electrical-to-optical conversion circuit 5, changes and variations in loss due to the length of the transmission line 2, variations in the gain of the optical-to-electrical conversion circuit 10, or deterioration, optical
The output voltage level of the electrical conversion circuit 10 varies greatly.

The threshold voltage is adjusted according to the change. Generally, the optimal value of the threshold voltage is the two values of the high level value and low level value of the received signal.
The value is close to 1/1.

If a signal other than the initialization signal is received, the initialization signal detection circuit 13 does not activate the dark value control circuit 12. The threshold control circuit 12 holds and outputs the threshold voltage immediately before deactivation. Since the threshold voltage does not change even if NRZ data including DC components is manually input, NRZ data can be received with optimal characteristics.

The voltage comparison circuit 11 compares the output level of the optical/electric conversion circuit 10 and the output dark value voltage of the threshold value control circuit 12, and discriminates between data "1" and data "0".The initialization signal sets the mark rate to 2. The initialization signal detection circuit 13 and threshold value control circuit 12 can be simplified by reducing the mark rate to 1/2.The mark rate does not necessarily have to be 1/2, but can be used as long as it is a constant value.

〔Effect of the invention〕

As explained above, according to the present invention, the threshold voltage of the optical receiver circuit is controlled when an initialization signal with a mark rate of 1/2 is received, and when a signal other than the initialization signal is received, the control is performed. By maintaining the set threshold voltage without
This has the effect of allowing data to be received with minimum bit error rate and pulse width distortion.

[Brief explanation of drawings]

The figure is a block diagram showing the configuration of an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Optical transmission circuit, 2... Optical transmission line, 3... Optical receiving circuit, 4... Selection circuit, 5... Electrical/optical conversion circuit, 6... Initialization signal generation circuit , 7... Switching signal input terminal, 8... NRZ data input terminal, 10... Optical.
Electrical conversion circuit, 11... Voltage comparison circuit, 12... Threshold control circuit, 13... Initialization signal detection circuit, 14...
・NRZ data output terminal.

Claims (1)

[Claims] 1. An optical transmission circuit, an optical transmission line for transmitting a transmission signal of this optical transmission circuit, and an optical reception circuit for receiving an optical signal from this optical transmission line, In an optical communication system for transmitting NRZ data, the optical transmission circuit includes an initialization signal generation circuit that generates an initialization signal with a mark rate of 1/2, and a binary NR input circuit.
a selection circuit that selects the Z data and the initialization signal and transmits the selected signal to the optical transmission line; A threshold control circuit that adjusts the threshold voltage so that pulse width distortion is minimized, and when a signal other than the initialization signal is received, maintains the threshold voltage set by the initialization signal and applies it to the voltage comparison circuit that discriminates the signal. An optical communication system characterized by the following.