Time Division Multiple Access (TDMA) using a high-speed packet signal for high-speed multimedia signal transmission has been actively studied. One of techniques for high-speed packet service is an optical subscriber network for efficiently providing various multimedia contents. Such an optical subscriber network uses a passive optical network (PON) technique.
In the PON technique, a single optical line terminal (OLT) and a plurality of optical network units (ONUs) are configured in a point-to-point (PTP) scheme. The PON technique is classified into APON (or BPON), EPON, and GPON according to protocols. The APON (ATM-PON) technique is based on an ATM protocol. The EPON (Ethernet-PON) technique provides uplink/downlink bandwidth of up to 1 Gbps through a cheap Ethernet and efficiently provides an Internet Protocol (IP) service through an Ethernet frame having a variable length. Gigabit-PON (GPON) efficiently transmits variable-length IP service and TDM service using a newly defined GPON encapsulation method (GEM) frame structure. In addition, the GPON transmits an ATM protocol without any additional overhead.
In order to reduce a subscriber cost, a central station of the PON system uses a single optical receiver to receive packet signals from a plurality of subscribers. Therefore, the received packet signals have different magnitudes and phases. These signals are referred to as burst signals. The burst signals are received through a burst mode receiver.
In a conventional PTP optical communication system, a decision threshold voltage is fixed to a constant by analog (AC) coupling an output of a linear channel to a decision circuit. In order to receive burst data using the optical receiver, an idle time must increase between packets. The idle time is a sum of a guard time and a preamble time. However, if the idle time increases, a packet transmission efficiency is reduced. When a capacity of a coupling condenser is reduced in order to decrease the idle time, another device for encoding/decoding outgoing data is required. In recent years, burst mode receivers have been developed which can process a plurality of different input signals within a short idle time and have a wide dynamic range.
According to the APON and GPON standards, the burst mode receiver has an external reset signal provided from a higher network layer. However, according to the EPON standard, the burst mode receiver has no external reset signal. In addition, an automatic gain controller (AGC) of the burst mode receiver forms a feedback loop to continuously control a gain of a transimpedance amplifier (TIA) according to an input level. Therefore, a frequency response of the TIA is affected by a characteristic of the feedback loop having a high sensitivity with respect to a process variation. The frequency response of the TIA is not smooth but flat in an entire operation range, causing a poor waveform in the output of the TIA. The burst mode receiver having the burst-based AGC using the external reset signal is not suitable for the EPON standard because the EPON system does not provide a reset.
Therefore, the PON system needs to generate the reset signal inside the receiver in order to obtain a high dynamic range within a short guard time. However, the conventional burst-based AGC and burst mode receiver are not suitable for application to an internal TO-can assembly because they have an internal reset signal have a large chip size.