EE 330 Lect 38 Fall 2011

EE 330 Lect 38 Fall 2011 - EE 330 Lecture 38 Digital...

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EE 330 Lecture 38 Digital Circuits Characterization of the CMOS Inverter
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Hierarchical Digital Design Domains: Behavioral: Structural : Top Bottom Physical Bottom Up Design Top Down Design Review from Last Lecture
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Representation of Digital Systems Standard Approach to Digital Circuit Design 1. Behavioral Description Technology independent 2. RTL Description (Register Transfer Level) (must verify (1) (2)) 3. RTL Compiler Registers and Combinational Logic Functions 4. Logic Optimizer 5. Logic Synthesis Generally use a standard call library for synthesis (sublevels 6-8 not shown on this slide) 8 – level representation Review from Last Lecture
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Representation of Digital Systems Standard Approach to Digital Circuit Design 1. Behavioral Description Technology independent 2. RTL Description (must verify (1) (2)) 3. RTL Compiler Registers and Combinational Logic Functions 4. Logic Optimizer 5.Logic Synthesis Generally use a standard call library for synthesis HDL Review from Last Lecture
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Logic Optimization • Number of Gates • Number or Levels of Logic • Speed • Delay • Power Dissipation • Area • Cost • Peak Current What is optimized (or minimized) ? Depends Upon What User Is Interested In  Review from Last Lecture
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The basic logic gates The characteristics of any gate logic family can be expressed rather simply in terms of the characteristics of the basic inverter in that logic family Review from Last Lecture
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Desirable and/or Required Logic Family Characteristics 1. High and low logic levels must be uniquely distinguishable (even in a long cascade) 2. Capable of driving many loads (good fanout) 3. Fast transition times (but in some cases, not too fast) 4. Good noise margins (low error probabilities) 5. Small die area 6. Low power consumption 7. Economical process requirements Review from Last Lecture
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Desirable and/or Required Logic Family Characteristics 8. Minimal noise injection to substrate 9. Low leakage currents 10. No oscillations during transitions 11. Compatible with synthesis tools 12. Characteristics do not degrade too much with temperature 13. Characteristics do not vary too much with process variations Are some of these more important than others? Yes ! – must have well-defined logic levels for circuits to even function as logic Review from Last Lecture
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What are the logic levels for a given inverter of for a given logic family? V H =? V L =? Can we legislate them ? Some authors choose to simply define a value for them Simple and straightforward approach But what if the circuit does not interpret them the same way they are defined !!
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What are the logic levels for a given inverter of for a given logic family? V H =? V L =? Can we legislate them ? Some authors choose to define them based upon specific features of inverter Analytical expressions may be complicated But what if the circuit does not interpret them the same way they are defined !!
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EE 330 Lect 38 Fall 2011 - EE 330 Lecture 38 Digital...

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