Design Of The 1.25Gbps Burst-mode Receiver Module For EPON System

Recent years, with the development of the Broad band, EPON, as a practical and effective resolving method to realize FTTH, has been studied largely. But the receiving of the optical burst-mode signal, as the key technology to realize the EPON system, has not been resolved well no matter in China or abroad. The traditionary burst-mode receiver technology for lower speed signal generally applies the method of DC-coupling. Because the method of DC-coupling could reflect the change of the burst signal quickly. But for the EPON burst signal which speed is as fast as 1.25Gb/s, by DC-coupling ,on the one side it must setup the proper threshold for the different signal packet in shorter interval, on the other side it must could reset the signal level timely so that it could receive the following signal packet well. These are both the technology problem to forbid the DC-coupling receiving, so that the chip for DC-coupling EPON burst receiving still has not been designed successfully.By the regulation of the EPON protocol 802.3ah, describing the characteristic of the EPON frame and data format detailedly, we designed the EPON burst-mode receiver module successfully by the method of AC-coupling. This paper applies two schemes to realize the burst-mode receiver module.The first scheme: using the general preamplifier for receiving the consecutive signal. In order to reflect for the burst signal timely, we discard the AGC circuit in the chip. The testing result shows that if we choose the proper the coupling capacitance, we could receive the burst signal correctly by this method. And the dynamic range could reach about -15dB. But because the AGC lose its function, It is hard to get higher overload optical power for the module.The second scheme: applying DC cancellation in the preamplifier. By feed the DC component of the signal out of the transimpedance amplifier back to the input of the preamplifier, we could control the signal current flowing into the transimpendance, so that the DC component in the signal is cancelled. As a result no matter the higher power optical signal or the low power optical signal, their DC components are on the same level. Applying the scheme, the influence on the receiving characteristic from the coupling capacitance is less, so that it makes the sensitivity of the module improved little. But the overload optical power gets improved largely. It could reach -1dBm and dynamic range reaches more than 25dB.In the meantime the factors which influence the signal receiving are described detailedly, such as jitter, the value of Q, SNR, data format and guarding time and so on.The result showed that the optical receiver module, which we had designed, has very high sensitivity and wider dynamic range. This module could meet the need of the EPON system. The method of AC-coupling avoids the technological problems which have to be resolved in the process of designing DC-coupling burst-mode optical receiver. In the EPON burst-mode applications, thisAC-coupling optical burst-mode receiver module could be an effective and cheapalternative method.