2. VLSI Basic Hiroaki Kunieda Dept. of Communication and Integrated Systems Tokyo Institute of Technology VLSI Design with Verification Specification System Design System Verification Logic Design Logic Verification Layout Design Layout Verification RTL Netlist Mask Data Test Data 1.3 Logic Gate Logic Gate Class Static Logic CMOS Logic Pseudo NMOS Logic NMOS Logic Dynamic Logic CMOS Domino Logic Characteristics Logic Delay Rise Time Fall Time Fan-in/ Fan-out Power Consumption Logic Theory [Completeness] •Function {|}=NAND function: complete •1: a|(a|a) = a|a’ = 1 •0: {a|(a|a}|{a|(a|a)} = 1|1 = 0. •a’: a|a = a’. •ab: (a|b)|(a|b) = ab •a+b: (a|a)|(b|b) = a’|b’=a+b •NOR function: complete •AND and OR function: not complete [Irredundant] no literal can be removed. redundant Ab+ab’=a Data sheet for 45nm Process Parameter Symbols Data Oxide Thickness Tox 1.3 (1.7) nm Unit MOS Capacitor Cox 15.67 fF/um2 Gate Capacitor (W=250nm, L=25nm) Cg 0.160 fF Sheet registance Rsheet 875 Ω/□ Relative permittivity εr 2.3 Vacuum permittivity ε0 8.85418782 pF/m NMOS On current(L=35nm) Ion(n) 1360uA/um PMOS Off current (L=35nm) Ion(p) 1070uA/um Off leak current (L=35nm) Ioff 100nA/um Data sheet for 45nm Process Parameter Symbols Data Power Supply Voltage VDD 1.0 V Gain factor K 7.81 uA/V2 Threshold voltage Vth 0.4 V Gate delay Tau 10 psec Unit on resistor (L=35nm) Ro 220.6 Ω-um Unit Capacitor (L=35nm) Co 45.3 fF/um Wire R Rline 500 Ω/mm Wire C Cline 300 fF/mm #layer for wire #layer 12 MOS “MOS” : sandwich structure of Metal, Oxide, and Silicon (semiconductor substrate). The positive voltage on the polysilicon forms gate attracts the electron at the top of the channel. The threshold voltage (Vt) collects enough electrons at the channel boundary to form an inversion layer (p -> n). Field Oxide Gate Oxide Transistor Parasitics Cg: gate capacitance = 0.9fF/μm2 (2 μprocess) Cgs/Cgd: source/drain overlap capacitance =Cox W (Cox: gate/bulk overlap capacitance) A Simple Transistor Model Linear region Vds Vgs Vt W 1 2 Id k ' [(Vgs Vt )Vds Vds ] L 2 Saturated region Id nMOS transistor become on by applying high voltage to gate to provide current. pMOS transistor becomes on by applying low voltage to gate to provide current Vds Vgs Vt 1 W k ' [(Vgs Vt ) 2 ] 2 L Static Complementary Gates VDD Pullup network (pMOS) •output is connected to VDD Ro/W CoW Ro/W CoW VSS Pulldown network (nMOS) •Output is connected to VSS Pull up Pull down Vin-Vout DC Characteristics VOH Noise Margin NML = VIL-VOL NMH = VOH-VIH VIH VOL VIL CMOS NAND & NOR Pullup network (pMOS) •output is connected to VDD when ab=0. VDD VSS Pulldown network (nMOS) •Output is connected to VSS when ab=1. Relation between nMOS and pMOS Dual graph And Or Inverter (AOI) gate (ab+c)’ Adders si =aibici =(aibi)ci = Pici ci+1=aici+bici+aibi=(aibi)ci+aibi =Pici+Gi 1.3 Gate Delay and Wire Delay Gate Delay (delay model) Let’s suppose that Wp = 2 Wn which makes the same pull up and pull down current with ON-resistance of, Ro/W where Ro is the resistance per unit width. (ex. 200 Ωum) Either one Becomes On. CoW Load capacitance consisting of drain junction capacitance is corresponded by the area of the drain such as CoW where Co is the capacitance per unit width (ex. 50 fF/um) Ro/W Ro/W CoW Input capacitance is also represented by CoW L=35 nm=0.035 um (45nm) Gate Delay Pull up current is represented by VDD/Ron(p). Pull down current is represented by VDD/Ron(n) Gate Delay (W=0.35um, L=0.035um) CoW Ro/W Either one Becomes On. = (Ro/W) x (CoW) Ro/W Ro/W = Ro Co CoW CoW Ro/W = 200 Ωum x 50 pF/um CoW Pull up Pull down = 10 psec Pull up/down currents are represented by ON resistance, which are reversely corresponded by the channel width W. 2 stage gates without load Either one Becomes On. CoW1 Ro/W1 Either one Becomes On. Ro/W1 The first term represents the delay of the 1st stage, where the output charge and the input charge of the 2nd stage is pull up or down by the current driven by the 1st gate. Both charge and current corresponds to the size or the channel width w. Ro/W2 Ro/W2 CoW2 CoW1 CoW2 Delay = 1st stage delay + 2nd stage delay = (Ro/W1) (CoW1+CoW2) + (Ro/W2)(CoW2) = RoCo (2+W2/W1) = 10 psec x 3 = 30 psec The second term represents the delay of the 2nd stage. Without any load to the gates, the delay becomes identical to, which depends on the process. 2 stage gates with load Load Capacitance is total sum of input capacitance CoWload Delay = 1st stage delay + 2nd stage delay = (Ro/W1) (CoW1+CoW2) + (Ro/W2)(CoW2+CoWload) = RoCo (2+W2/W1+Wload/W2) Case 1. W2=W1, Load=10W1 Delay = 10 psec (2+1+10) = 130.0 psec Case 2. W2=3W1, Load=10W1 Delay = 10 psec (2+3+3.33) =83.3 psec Wires Delay Elmore Delay Model Delta1=r1 x (C1+---+Cn) =n tc Delta2=r2 x (C2+----+Cn) =(n-1)tc DeltaN=rn x Cn =tc total=Delta1+ ----- + DeltaN =[n(n+1)/2] tc Wire Delay Rline=2.0 Ω-um Cline=0.3 fF/um Ro=200 Ω*um Co= 50 fF/um W1=W2=0.35u Line=2N um Delay=(R0/W1) (CoW1+CoW2+ClineLine) +(RlineLine) (CoW2+(Cline/2)Line) =200 x (2x50f + 2xN)+2 x (10f+0.5N) = 50 nsec + 26*N nsec (line =2xN um) Delay = Ro/W1 (CoW1+CoW2) =2.5K x 20fF =50.0 nsec (line=0) Wire Delay Rline=500 Ω/um Cline=300 fF/um Ro=25 kΩ*um Co=0.5 fF/um W1=W2=0.35u Line=0.5um Delay=(R0/W1) (CoW1+CoW2+ClineLine) +(Ro/W1+RlineLine) (CoW2+(Cline/2)Line) =50K x (0.5 f + 50K x (0.25+0.125) = 37.5 nsec + 18.8 nsec =56.3 nsec (line =0.5 um) Delay = Ro/W1 (CoW1+CoW2) =50K x 0.5fF =25 nsec (line=0) 1.4 Flipflop and Memory Switch Logic Logic 0 transfer Logic 1 transfer Latch Charge sharing: the stored data of A is connected to the latch’s output. Additional buffer may be required to drive output load. Clocked Inverter tristate inverter produces restored output or HiImpedance Z Used as latch circuit Latch D Flip-flop Operation Scan in DFF Functional Schematic of DFF with Scan 31 ACSEL Lab University of California, Davis Memory Structure Read-Only Memory (ROM) Random Access Memory (RAM) Static RAM (SRAM) Dynamic RAM (DRAM) Static RAM Cell •Read •Precharge bit and bit’ •Asert Select line •Write •Bit and bit’ lines are set to desired values. •Select is set to 1. RAM Cell Write set bit line Read Precharge firstly bit line Activate word line 1.5 Data Path and Control Circuit Data Path 1 Control Sequential Logic Circuit Data Path 2 0 1 2 3 4 5 6 7 DA1 DB1 * DC1 DA2 DB2 * DC2 LoadA 1 0 0 0 1 0 0 0 RegA * DA1 DA1 DA1 DA1 DA2 DA2 DA2 LoadB 0 1 0 0 0 1 0 0 RegB * * DB1 DB1 DB1 DB1 DB2 DB2 LoadC 0 0 1 0 0 0 1 0 RegC * * * DC1 DC1 DC1 DC1 DC2 BUS During Clk=2, adder operation must be completed within 1 clock. 1.6 Design and Verification