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EE415 VLSI Design Harris Semiconductor Field Trip to Harris Semiconductor Monday (February 28th) Leave at 9:00 AM from Stocker There will be a class on the 25th!! Will discuss Quiz 3 Tour from ~1:30 PM to 4 PM Arrive in Athens after 8PM Bring cash for food No MAKE-UP please
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EE415 VLSI Design Read 4.1, 4.2 Start Reading 4.3 (dynamic CMOS) COMBINATIONAL LOGIC
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EE415 VLSI Design As long as Fan-out Capacitance dominates Progressive Sizing: Can Reduce Delay by more than 30%! Example 4.3: no sizing: t pHL = 1.1 nsec with sizing: t pHL = 0.81 nsec Fast Complex Gate - Design Techniques
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EE415 VLSI Design Fast Complex Gate - Design Techniques Transistor Ordering
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EE415 VLSI Design Fast Complex Gate - Design Techniques Improved Logic Design
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EE415 VLSI Design Fast Complex Gate - Design Techniques Buffering: Isolate Fan-in from Fan-out C L C L Read Example 4.5
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EE415 VLSI Design Ratioed Logic V DD V SS PDN In 1 2 3 F R L Load Resistive N transistors + Load V OH = V DD V OL = R DN R + R L Asymmetrical response Static power consumption t pLH = 0.69 R L C L V DD
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EE415 VLSI Design Ratio Based Logic Problems with Resistive Load I L = (V DD – V out) / R L Charging current drops rapidly once V out starts to rise Solution: Use a current source! Available current is independent of voltage Reduces t pLH by 25%
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EE415 VLSI Design Load Lines of Ratioed Gates
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EE415 VLSI Design Active Loads
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EE415 VLSI Design Active Loads Depletion mode NMOS load V GS = 0 I L ~ (k n, load / 2) (|V Tn |) 2 Deviates from ideal current source Channel length modulation Body effect V SB != V DD varies with V out reduces |V Tn |, hence I L for increasing V out
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EE415 VLSI Design Active Loads Pseudo-NMOS load No body effect, V SB = 0V V GS = - V DD, higher load current I L = (k p / 2) (V DD - |V Tn |) 2 Larger V GS causes pseudo-NMOS load to leave saturation mode sooner than NMOS
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EE415 VLSI Design Pseudo-NMOS For Vin = V DD : NMOS linear PMOS saturated Read PP 206, 207, Example 4.6
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EE415 VLSI Design Pseudo-NMOS NAND Gate V DD GND Out
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EE415 VLSI Design Improved Loads Standby mode reduces power dissipation
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EE415 VLSI Design Improved Loads (2) Dual Cascode Voltage Switch Logic (DCVSL)
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EE415 VLSI Design Example B AA B BB Out XOR-NXOR gate
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EE415 VLSI Design Pass-Transistor Logic I n p u t s Switch Network Out A B B B N transistors No static consumption
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EE415 VLSI Design NMOS-only switch V TN
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EE415 VLSI Design Solution 1: Transmission Gate A B C C A B C C
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EE415 VLSI Design Resistance of Transmission Gate
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EE415 VLSI Design Pass-Transistor Based Multiplexer GND V DD In 1 In 2 SS S S
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EE415 VLSI Design Transmission Gate XOR
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