Double-edge pulsewidth modulation for multidrop backplanes

Multilevel signaling, such as pulse amplitude modulation (4-PAM), has been actively surveyed in the band-limited channels with sharp frequency roll-off. Due to the longer symbol period, multilevel signalling requires a lower channel bandwidth and offers a better spectral efficiency. This paper discusses a different type of multilevel modulation - double-edge pulsewidth modulation (DPWM), which encodes symbols into time domain on both rising/falling transition edges. DPWM offers the same spectral efficiency achieved by 4-PAM and resolves the dynamic range constrain for 4-PAM in advanced CMOS technology. In this paper, we demonstrate the benefits of using DPWM in the multidrop bus backplanes which form the channels with sharp attenuation dips because of multiple impedance discontinuities.