Avt. Cartaxo et Aa. Dealbuquerque, JITTER IN THE SQUARE SYNCHRONIZER ON DIRECT-DETECTION OPTICAL COMMUNICATIONS .3. NUMERICAL RESULTS CONCERNING WHITE CIRCUIT NOISE, IEE proceedings. Optoelectronics, 141(6), 1994, pp. 394-400
Theoretical assessment of the square synchroniser performance, develop
ed in a previous paper, is used to present and discuss numerical resul
ts in the presence of white circuit noise. This fully analytical metho
d permits the optimal design (i.e. minimising timing jitter) of square
synchronisers, taking into account all the relevant parameters, for d
irect detection optical communication systems. A thorough physical exp
lanation of the presented results and their relevance for practical re
ceiver design is provided. The work is increasingly important nowadays
because multigigabit per second transmission rates are being used on
direct detection optical systems. It is shown that, for low signal-to-
noise ratios and under quite general conditions, the performance of th
e square synchroniser is better in a signal shot-noise-dominant situat
ion (typical of long-distance communications with APD receivers), foll
owed by the white-circuit-noise-dominant situation (typical of long-di
stance communications with PIN receivers), and is worst for the dark c
urrent-noise-dominant situation (typical of germanium APD receivers).
The noise contribution to square synchroniser performance can be very
high. The timing jitter properties respecting the circuit noise domina
nt situation usually hold also on the signal shot-noise dominant situa
tion, except for a very narrow (compared with the bit period) optical
pulse shape incident on the photodetector.