Idle Sequence in a Serial Link Optimized to Reduce Electromagnetic Interference
Original Publication Date: 1995-Dec-01
Included in the Prior Art Database: 2005-Mar-31
Barrett, WM: AUTHOR [+2]
A method and apparatus for pseudo-randomizing the idle sequence in a fiber optic communication link is disclosed. This is done for the purpose of reducing the Electromagnetic Interference (EMI) levels of the system involved.
Idle Sequence in a Serial Link Optimized to Reduce
A method and
apparatus for pseudo-randomizing the idle sequence
in a fiber optic communication link is disclosed. This is done for
the purpose of reducing the Electromagnetic Interference (EMI) levels
of the system involved.
In a fiber
optic communication link, the "data" being
transmitted can typically be classified into two groups:
1. Actual or real data, that comes in bursts. This is usually
termed a packet or frame of data. A packet contains
information surrounded by data containing: delimiters,
addressing/routing information, error-correction bits, etc.
2. Idle or null data. This is what is transmitted between the
packets of information. The main purpose of this null data
(herein called the "idle sequence") is to maintain sufficient
transitions (0's -> 1's and 1's -> 0's) so that the receiving
can continue to extract the clock from the bit stream (i.e.,
maintain bit synchronization).
method of generating the idle sequence is to
constantly transmit a specific "byte" of information. Since the main
objective is to have a high transition rate, one possible idle byte
would be one with alternating 1's and 0's (i.e., '0101010101'b if
10-bit encoded bytes are utilized). Regardless of the specific byte
pattern used during the idle sequence, the fact that a constant
pattern is repetitively transmitted introduces the exposure of
increased EMI levels coming from the transmitting and receiving ends
of the communication link.
described in this report presents the idea of
pseudo-randomizing the idle sequence. Instead of transmitting a
constant idle pattern (i.e., repeating a specific byte), the idle
pattern should always be changing (i.e., adjace...