Work out bit error rate from snr instantly with clear inputs, formula shown and shareable results.
Bit error rate follows the Gaussian tail: BER = Q(sqrt(SNR)) for NRZ. PAM4 packs two bits per symbol but its eyes are a third the height, costing about 9.5 dB of SNR — the fundamental trade that makes PAM4 harder despite doubling throughput per baud.
BER from SNR
BER = Q(sqrt(SNR)); PAM4 suffers a 9.54 dB amplitude penalty versus NRZ
Three eyes stacked in the same amplitude means each is one third the height, and 20log10(3) is 9.54 dB of SNR penalty.
It doubles the bits per symbol, halving the Nyquist frequency and therefore the channel loss, which above about 25 GBaud more than compensates for the SNR penalty.