An SNR-Enhanced 8-Ary (SNRE-8) Modulation Technique for Wireline Transceivers Using Pulse Width, Position, and Amplitude Modulation

This article presents a novel eight-ary modulation technique with improved signal-to-noise ratio (SNR) compared to conventional pulse amplitude modulation 8 (PAM-8). The proposed SNR-enhanced 8-ary (SNRE-8) scheme modulates pulse width, position, and amplitude to improve the SNR. The proposed SNRE-8 modulation leverages the wireline channel loss to perform the modulation. Digital decoding of mutually exclusive eyes generated by the proposed SNRE-8 modulation further improves the eye margin at the receiver. A 27-Gb/s transceiver is implemented in a 65-nm CMOS process employing the proposed modulation. A PAM-8 transmitter is implemented on the same chip for comparison purposes. Compared to the PAM-8 modulation, the proposed SNRE-8 modulation shows an average SNR improvement of 10.6 dB at the near-end eye at the cost of 6.6% eye width reduction. With the aid of a time-domain feed-forward equalizer (FFE) and a continuous-time linear equalizer (CTLE), the proposed SNRE-8 transceiver achieves a bit error rate (BER) of
$10^{-8}$
on a 9-dB loss channel with an energy efficiency of 5.39 pJ/bit.