Berkeley ELENG 141 - Lecture 6 Inverter Delay Optimization (13 pages)

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Lecture 6 Inverter Delay Optimization



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Lecture 6 Inverter Delay Optimization

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Pages:
13
School:
University of California, Berkeley
Course:
Eleng 141 - Introduction to Digital Integrated Circuits
Introduction to Digital Integrated Circuits Documents

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EE141 Fall 2009 Digital Integrated Circuits Lecture 6 Inverter Delay Optimization EE141 EECS141 Lecture 6 1 1 Announcements Lab 2 Mon Tues Lab 3 Fri Homework 3 due Thursday Homework 4 due next Thursday EE141 EECS141 Lecture 6 2 2 Class Material Last lecture Overview of Semiconductor Memory Today s lecture Inverter Delay Optimization Reading 5 4 5 5 EE141 EECS141 3 Lecture 6 3 Inverter Chain In Out CL For some given CL How many stages are needed to minimize delay How to size the inverters Anyone want to guess the solution EE141 EECS141 Lecture 6 4 4 Careful about Optimization Problems Get fastest delay if build one very big inverter So big that delay is set only by self loading Likely not the problem you re interested in Someone has to drive this inverter EE141 EECS141 Lecture 6 5 5 Engineering Optimization Problems in General Need to have a set of constraints Constraints key to Making the result useful Making the problem have a clean solution For sizing problem Need to constrain size of first inverter EE141 EECS141 Lecture 6 6 6 Delay Optimization Problem 1 You are given A fixed number of inverters The size of the first inverter The size of the load that needs to be driven Your goal Minimize the delay of the inverter chain Need model for inverter delay vs size EE141 EECS141 7 Lecture 6 7 Inverter Delay Minimum length devices L 0 09 m Assume that for WP 2WN 2W approximately equal resistances RN RP approx equal rise and fall delays tpHL tpLH Analyze as an RC network L L RP Rsq p RN Rsq n WP WN 2W W RW Delay tpHL ln 2 RNCL tpLH ln 2 RpCL Loading on the previous stage Cin 3WC g EE141 EECS141 Lecture 6 8 8 Inverter Delay CP 2WCg L RW Rsq n W 2W Cint 3WCd W Cint CL Cin 3WC g CN WCg Replace ln 2 with k a constant Delay kRWCint kRWCL Delay kRsq n L W 3WCd kRsq n L W CL EE141 EECS141 9 9 Lecture 6 Inverter with Load CP 2WCg Delay 2W W Cint CL Load CN WCg Delay kRW Cin Cint Cin CL Cin 3kLRsq nCg Cd Cg CL 3WCg Delay Internal Delay Load EE141 EECS141 Lecture 6 10 10 Delay



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