Spring 2012, Apr 4 . . . Spring 2012, Apr 4 . . . ELEC 7770: Advanced VLSI Design ELEC 7770: Advanced VLSI Design (Agrawal) (Agrawal) 1 ELEC 7770 ELEC 7770 Advanced VLSI Design Advanced VLSI Design Spring 2012 Spring 2012 Power and Ground Power and Ground Vishwani D. Agrawal Vishwani D. Agrawal James J. Danaher Professor James J. Danaher Professor ECE Department, Auburn University ECE Department, Auburn University Auburn, AL 36849 Auburn, AL 36849 [email protected]http://www.eng.auburn.edu/~vagrawal/COURSE/E77 70_Spr12
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Spring 2012, Apr 4...ELEC 7770: Advanced VLSI Design (Agrawal)1 ELEC 7770 Advanced VLSI Design Spring 2012 Power and Ground Vishwani D. Agrawal James J.
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ReferencesReferences Q. K. Zhu, Q. K. Zhu, Power Distribution Network Design for VLSIPower Distribution Network Design for VLSI, Hoboken, New , Hoboken, New
Jersey: Wiley, 2004.Jersey: Wiley, 2004. M. Popovich, A. Mezhiba and E. G. Friedman, M. Popovich, A. Mezhiba and E. G. Friedman, Power Distribution Power Distribution
Networks with On-Chip Decoupling CapacitorsNetworks with On-Chip Decoupling Capacitors , Springer, 2008., Springer, 2008. C.-K. Koh, J. Jain and S. F. Cauley, “Synthesis of Clock and C.-K. Koh, J. Jain and S. F. Cauley, “Synthesis of Clock and
Power/Ground Network,” Chapter 13, L.-T. Wang, Y.-W. Chang and K.-Power/Ground Network,” Chapter 13, L.-T. Wang, Y.-W. Chang and K.-T. Cheng (Editors), T. Cheng (Editors), Electronic Design AutomationElectronic Design Automation, Morgan-Kaufmann, , Morgan-Kaufmann, 2009. pp. 751-850.2009. pp. 751-850.
J. Fu, Z. Luo, X. Hong, Y. Cai, S. X.-D. Tan, Z. Pan, “J. Fu, Z. Luo, X. Hong, Y. Cai, S. X.-D. Tan, Z. Pan, “VLSI On-Chip VLSI On-Chip Power/Ground Network Optimization Considering Decap Leakage Power/Ground Network Optimization Considering Decap Leakage Currents,” Currents,” Proc. Asia and South Pacific Design Automation Conf.Proc. Asia and South Pacific Design Automation Conf. , , 20052005 , pp. 735-738., pp. 735-738.
Decoupling CapacitorDecoupling Capacitor A capacitor to isolate two electrical circuits.A capacitor to isolate two electrical circuits. Illustration: An approximate model:Illustration: An approximate model:
where where αα and and ββ are technology parameters. are technology parameters.
RdRd == VL(t)/IgateVL(t)/Igate
Because V(t) is a function of time, Rd is Because V(t) is a function of time, Rd is difficult to estimate. The decoupling difficult to estimate. The decoupling capacitance is simulated in spice.capacitance is simulated in spice.
Increase wire width to reduce resistance:Increase wire width to reduce resistance: Control voltage drop for given currentControl voltage drop for given current Reduce resistive lossReduce resistive loss
Reduce wire width to reduce wiring area.Reduce wire width to reduce wiring area. Minimum width restricted to avoid metal Minimum width restricted to avoid metal
Where n = number of branches in power networkwi = metal width of ith branchsi = length of ith branchρ = metal resistivityCi = maximum current in ith branchxi = voltage drop in ith branch
Subject to several conditions.
Condition 1: Voltage DropCondition 1: Voltage Drop
Where wi = metal width of ith branchsi = length of ith branchρ = metal resistivityCi = maximum current in ith branchxi = voltage drop in ith branchW = minimum line width
Condition 3: Metal MigrationCondition 3: Metal Migration
Do not exceed maximum current to wire-width ratio:
Ci / wi = xi /(ρ si) ≤ σi
Where wi = metal width of ith branchsi = length of ith branchρ = metal resistivityCi = maximum current in ith branchxi = voltage drop in ith branchσi = maximum allowable current density
Initial charge on Cd, QInitial charge on Cd, Q00 = Cd VDD = Cd VDD
I(t): current waveform at a nodeI(t): current waveform at a node T: duration of currentT: duration of current Total charge supplied to load:Total charge supplied to load:
Assume that charge is completely supplied by Cd.Assume that charge is completely supplied by Cd. Remaining charge on Cd = Cd VDD – QRemaining charge on Cd = Cd VDD – Q Voltage of supply node = VDD – Q/CdVoltage of supply node = VDD – Q/Cd For a maximum supply noise For a maximum supply noise ΔΔVDDmax,VDDmax,