PAM5 method
The PAM5 method is a Multi Level Coding( MLC) used in Gigabit Ethernet over TP cables. In order to be able to transmit Gigabit Ethernet over Cat-5 cables, it is necessary to keep the transmission frequency below 100 MHz at the intended bandwidth of 250 Mbps.
The PAM5 coding is a quaternary coding in which two bits are transmitted as dibits with four different voltage levels in each case. The bit combinations 00, 01, 10 and 11 have four different voltage values during transmission and thus correspond to four dibits. The fifth state is given at a transmission level of zero and is used for error correction in this method.
The two-bit combination results in a transmission rate of 125 MDibits/s for a data rate of 250 Mbit/s and, since two dibits are transmitted for each signal cycle, a transmission frequency of 62.5 MHz reduced by half.
Since the transmitted signals are ground on the cables, decoding the dibits is not without problems. PAM5 is used in 100Base- T2 and 1000Base-T.