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ESE370: Circuit-Level Modeling, Design, and Optimization for Digital Systems
Day 23: November 2, 2012 Pass Transistor Logic: part 2 (Cascading without Buffers) Penn ESE370 Fall DeHon
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Previously Penn ESE370 Fall DeHon
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Two XOR Gates Penn ESE370 Fall DeHon
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Today Pass Transistor Circuit Transmission gates Tristate gates
Output levels Cascading Series pass transistors? Delay Transmission gates Tristate gates Penn ESE370 Fall DeHon
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Cascading Pass Transistors
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Chain without Inverters
What if we did this? Penn ESE370 Fall DeHon
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Extract key path Penn ESE370 Fall DeHon
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t=0 (after Vin transition 10)
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t=4t (after Vin transition 10)
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t=∞ (after Vin transition 10)
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Focus on Pass tr Vgs? Operation mode? Current flow?
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Voltage of Chain What is voltage at output?
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How compare Compare Penn ESE370 Fall DeHon
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DC Analysis Penn ESE370 Fall DeHon
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DC Analysis – chain of 6 Penn ESE370 Fall DeHon
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Conclude Can chain any number of pass transistors and only drop a single Vth Penn ESE370 Fall DeHon
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Transient Penn ESE370 Fall DeHon
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Closeup Penn ESE370 Fall DeHon
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Capacitance What is Capacitance per stage (@y)?
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Delay Delay as a function of chain length?
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Compare CMOS Buffered Pass TR Unbuffered Pass TR Delay Area
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Pass TR Tree What if we did this? Penn ESE370 Fall DeHon
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Path What’s different about this? Penn ESE370 Fall DeHon
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Gate Cascade? What are voltages? Penn ESE370 Fall DeHon
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Demonstration Circuit
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SPICE TODO show spice results of voltages
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Demonstration Chain Penn ESE370 Fall DeHon
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Spice Penn ESE370 Fall DeHon
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Conclude Cannot cascade degraded inputs into gates.
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Midterm 2 Topics Tau-model Logic Elmore-delay Scaling Energy and power
Estimation and optimization Elmore-delay Energy and power Dynamic and static Logic CMOS Ratioed Pass transistor Scaling Noise Margins No clocking Except to motivate delay targets and power calculations Note: 2010 midterm and 2011 midterm2 Penn ESE370 Fall DeHon
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Time Permitting… Penn ESE370 Fall DeHon
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Other Gates Penn ESE370 Fall DeHon
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Other gates What does this do? B A More examples in book.
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Pass Rail-to-Rail Penn ESE370 Fall DeHon
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Transmission Gate Voltage levels at output?
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Bus Drivers Penn ESE370 Fall DeHon
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Tristate Driver Penn ESE370 Fall DeHon
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Tri-State Drivers Penn ESE370 Fall DeHon
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Idea There are other circuit disciplines
Can use pass transistors for logic Even chains of pass transistors Sometimes gives area or delay win Do not cascade as easily as CMOS Penn ESE370 Fall DeHon
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Admin Project Daylight Savings Time change this weekend
Due Saturday Daylight Savings Time change this weekend …get an extra hour to study for… Midterm 2: Nov. 7th Evening Wednesday Penn ESE370 Fall DeHon
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