AC Coupling Circuit DC Balanced Patterns Optical Networks
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Solution Overview
Problem
Existing AC coupling techniques in high-speed optical networks, such as Gigabit PON, face issues with baseline wander and data loss due to biased DC levels and the use of capacitors, particularly when transmitting long sequences of identical bits, leading to inefficient data transmission and loss of information during laser activation or deactivation.
Innovation Solution
Implementing a method that uses DC balanced patterns before and after high-speed burst data signals to enable AC coupling, ensuring that the AC coupling circuit maintains signal integrity and does not alter the burst data, by generating a fill-in pattern when no data is transmitted, a second pattern to enable the optical transmitter, and a third pattern to disable it, all while maintaining DC balance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If AC coupling circuit with capacitors is used to remove biased DC level, then DC level filtering is improved, but baseline wander occurs and data loss happens during long sequences of identical bits
Solution Approach 1:
The patent applies preliminary action by transmitting a first DC-balanced training sequence before the actual data transmission. This training sequence pre-charges the coupling capacitors and establishes the correct baseline voltage level, preventing baseline wander during subsequent data transmission. The MAC module generates this training sequence with equal numbers of 0s and 1s to ensure DC balance before switching to normal data mode.
Solution Approach 2:
The patent implements periodic action by inserting DC-balanced sequences (training sequences and idle sequences) at regular intervals during data transmission. These periodic DC-balanced sequences reset the baseline voltage level and recharge the coupling capacitors, preventing cumulative baseline wander effects during long transmissions. The idle sequences between burst transmissions also maintain DC balance to prepare for the next transmission.
2Reliability
If DC balanced codes are used to decode transmitted data, then baseline wander is reduced, but data loss occurs during the beginning of burst and decoding complexity increases
Solution Approach 1:
The patent extracts the DC-balancing function from the data payload itself and places it in dedicated training sequences and idle sequences. Instead of requiring DC-balanced codes for the entire transmission including data, the solution separates the DC-balancing requirement to specific control sequences, allowing the actual data to be transmitted in its original format without complex DC-balanced encoding or decoding.
Solution Approach 2:
The patent introduces DC-balanced training sequences as an intermediary between the data source and the AC coupling circuit. These training sequences act as a mediator that prepares the AC coupling circuit for incoming data by establishing proper baseline levels, eliminating the need for complex DC-balanced decoding of the actual data payload.
3Productivity
If low-logic value signal is transmitted when no data is output, then transmitter disabling is achieved, but baseline wander occurs during laser activation and deactivation
Solution Approach 1:
The patent applies preliminary action by transmitting a DC-balanced idle sequence before the actual data burst transmission. This idle sequence pre-charges the coupling capacitors and establishes the correct baseline voltage level, ensuring that when the laser is activated for data transmission, the baseline is already stabilized and no wander occurs during the transition.
Solution Approach 2:
The patent changes the parameter of the idle signal from a simple low-logic value to a DC-balanced sequence with equal numbers of 0s and 1s. This parameter change ensures that the idle sequence maintains zero DC offset, preventing baseline wander during laser activation and deactivation while still serving the function of indicating no data transmission.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively transmits high-speed burst data signals without data loss, ensuring the AC coupling circuit does not alter the burst data, and maintains signal integrity, addressing the limitations of existing techniques by preventing baseline wander and ensuring accurate data transmission.
Implementation Method 1
an AC coupling circuit 230 is utilized to interface between the MAC module 210 and the optical transceiver 220. The AC coupling circuit 230 is comprised of serial capacitors and resistors connected in the data path between the MAC module 210 and the optical transceiver 220. The AC coupling is required to filter and block DC and low frequency signals.
Implementation Method 2
use of coupling capacitors may cause base line wander problems to occur when a long string of information is repeatedly included in a sequence of identical bits
Data Source
AI summary
A method for enabling alternating current (AC) coupling of high-speed burst data signals transmitted by an optical network unit (ONU). The method comprises generating a first data pattern to be sent to an optical transceiver through an AC coupling circuit, wherein the first data pattern is a direct current (DC) balanced pattern; generating a second data pattern to be sent to the optical transceiver through the AC coupling circuit, wherein the second data pattern is output prior to transmission of a high-speed burst data signal; and generating a third data pattern to be sent to the optical transceiver through the AC coupling circuit, wherein the third data pattern is output posterior to the transmission of the high-speed burst data signal.