Comparative Bypass Networks

SERDES transmit power supplies:

  • 13 X2Y® Capacitors replace 38 0402 caps
  • Plane inductance saturation for each supply is achieved w/ 2 X2Y® capacitors

Comparative Bypass Networks

X2Y vs. MLCCs
MLCC Design
MLCC Design
X2Y Design
X2Y® Design
Transmit Analog: VCCH

X2Y® Design

  • – 2 x 330uF tantalum caps
  • + 2 MLCCs + 7 X2Y®
  • – 1D < 80mOhms
  • equivalent resistive to 250MHz
    • Ignores spatial effects and IC parasitics
    • Spatial effects dominate above 10MHz
Transmit Analog: VCCH
Impedance Comparisons w/o IC

2-3X lower impedance 20MHz-100MHz w/ 7 caps instead of 20

  • >2.5:1 Higher FRES
  • 2.5:1 reduction in Q

Impedance Comparisons w/o IC

Original VCCTX and X2Y® Networks
Measured VCCTX Networks vs Simulated Shorted perimeter

Original network, FDTIM

  • LBYPASS decreases with increasing freq.
  • Near 20MHz about LTOTAL about 220pH
  • Die / bypass PRF near 200MHz
  • Bypass / PCB PRF near

X2Y® network selective zeroes

  • Lower LBYPASS @ 20MHz up
  • Zero for Die / bypass PRF
  • Zero for PCB / bypass PRF
VCCTX PCB / Bypass Resonance
Measured VCCTX Networks vs Simulated Shorted perimeter

Original network

  • @ relatively low PRF

X2Y® Network

  • Lower distributed L of 6/7 X2Y® caps raises to 580MHz
  • Suppressed w/ single 100pF rated X2Y®
    • Good suppression w/ conventional caps difficult due to high Q
  • Measured results, PRF completely suppressed
3.125Gbps Performance PRBS7

X2Y® Redues jitter to 32ps p-p jitter

  • vs 49ps in reference design

3.125Gbps Performance PRBS7 1 minute captures

X2Y® improves better eye amplitude >5%

  • 870mV pp @ sample point vs 820mV pp reference

3.125Gbps Performance PRBS7 870mV 1 minute captures

3.125Gbps Performance PRBS23

Shows same improvements in jitter and eye amplitude:

  • X2Y® 32ps p-p jitter vs 49ps in reference design
  • X2Y® 870mV pp vs 820mV pp in reference design

3.125Gbps Performance PRBS23 1 minute captures