Adaptive compensator for simultaneous switching noise in multi-channel transmitters

Abstract

Bandwidth of memory interface is growing to be wider, with increasing requirements on low I/O power consumption and immunity to simultaneous switching noise (SSN). Low-swing voltage-mode transmitters are an attractive choice regarding their low power consumption, but exhibits a trade-off in lowered immunity to SSN. Low-dropout (LDO) regulator and decoupling capacitor (de-cap), are conventionally utilized to attenuated the SSN in multi-channel transmitters, but the power distribution network (PDN) impedance cannot be perfectly flattened in all frequency range, and de-cap exhibits considerable amount of area especially in the sub-micron process. In this paper, SSN in multi-channel transmitters with LDO regulated supply is analyzed and a switching capacitor (SC) based pull-up current ($I_PU$) compensation technique is proposed to lower the SSN in all frequency range. A sign-sign LMS (SS-LMS) based adaptation technique is also proposed to enable on-chip adaptation on deciding the optimal strength of $I_PU$ compensation. Results from a simulation with $28nm$ CMOS on 4 parallel TXs shows that SSN is decreased from $9.8mV_rms$ to $2.3mV_rms$ utilizing only $20pF$ de-cap, with the proposed compensation technique.