Calculation of Test Receiver Parameters.

IBM CMOS6SF LVPECL Driver and Receiver

NOTE: in AC coupled simulations, this driver gave very assymetric results, with transmission line reflections. Source termination was used to significantly reduce these effects.

From the IBM spec sheet:

• Vdd = 3.3V (Core Vdd = 2.5V)
• V(common mode) = 1.85V to 2.15V (2.00V nominal)
• deltaV(driver) min=600mv, max=1100mv
• f(max) = 1000MHz, T(trans) = .25ns (not spec'd, calculated at 1/4 cycle time)

Calculate receiver deltaV with source termination for DC path:

• deltaV(max) = .5 * deltaV(driver)(max) = .5*1100mv = 550mv
• deltaV(min) = .8 * .5 * deltaV(driver)(min) = .8*.5*600mv = 240mv
  NOTE: if source termination is not required, both of these voltages are doubled.

Calculate hysteresis voltages and times:

• T(hyst) = 5 * T(trans) = 5*.25ns = 1.25ns
• V(hyst-edge) = .7 * deltaV(min) = .7*240mv = 168mv
• V(hyst-level) = .5 * V(hyst_edge) = .5*168mv = 84mv
  NOTE: if source termination is not required, both of these voltages are doubled.

Looking up values from Table 2 and Table 3 of P1149.6 Standard:

• HP_LP_Ratio = 2
• HP_Mult = 18
• LP_Mult = 9

Calculating the time constants:

• T(lp) = LP_Mult * T(hyst) = 9*1.25ns = 11.25ns
• T(hp) > HP_LP_Ratio * T(lp) = 2*11.25ns = 22.5ns
• T(test) > 3 * T(lp) = 3*11.25ns = 33.75ns

Calculating the R's and C's:

• Unless otherwise stated, R(bias) = 10Kohm to Vtt (= V(common mode))
• For normal board coupling (cap before termination):
  • Low-pass: C = 1pf, R = (11.25e-9)/(e-12) = 11.25Kohm
  • High-pass: R = 50ohm, C > (225e-10)/50 = 450pf
    (for "High frequency" simulations, C = 20nf)
• For board coupling with cap after termination, no source termination:
  • Low-pass: C = 1pf, R = (11.25e-9)/(e-12) = 11.25Kohm
  • High Pass: R = 10Kohm||11.25Kohm = 5294ohm, C > (225e-10)/5294 = 4.25pf
    (for "High Frequency" simulations, C=1000pf)
• For "on-chip" coupling, no low pass filter, no source termination:
  • HP_Mult = 6
  • T(hp) = 6*(1.25e-9) = 7.5ns
  • Assume C = 1pf (note: at this level, there will be voltage sharing between this capacitor and the inputs of the receivers.
  • High Pass: R = (7.5e-9)/(e-12) = 7500 Ohms