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ECE382 (Spring 00):Large-Scale Digital Integrated Circuit Design

ECE382 (Spring 00):Large-Scale Digital Integrated Circuit Design. Professor Naresh Shanbhag Department of Electrical and Computer Engineering University of Illinois at Urbana-Champaign Urbana, IL-61801. Lecture 8 : MOSFET Small Signal Models. 2. =. =. I. I. s. ,. P. P. s. ,. D. ,.

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ECE382 (Spring 00):Large-Scale Digital Integrated Circuit Design

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  1. ECE382 (Spring 00):Large-Scale Digital Integrated Circuit Design Professor Naresh Shanbhag Department of Electrical and Computer Engineering University of Illinois at Urbana-Champaign Urbana, IL-61801 Lecture 8 : MOSFET Small Signal Models

  2. 2 = = I I s , P P s , D , scaled D , original D , scaled D , original = PD PD . scaled original After scaling Before scaling = = I sI , P sP , D , scaled D , original D , scaled D , original 3 = PD s PD . scaled original Review: Deep Submicron Effects • Scaling types: constant field, constant voltage and hybrid • constant field: • constant voltage:Reliability problems such as electro migration, hot-carrier degradation and oxide break down. • Small geometry effects: short-channel and narrow-channel effects SCALING

  3. Review: Deep Submicron Effects(contd..) • Small geometry effects: short-channel and narrow-channel effects • short-channel effects: velocity saturation, mobility degradation and Vtreduction. • narrow-channel effects: Vt increase. • Impact on MOSFET I-V properties: reduction in saturation current, increase in subthreshold current.

  4. Outline • Motivation: • analog blocks exist (sense amps in memories) and more are appearing in digital systems (PLLs). • high-speed digital design (low-swing differential logic, gain vs. bandwidth vs. noise-immunity trade-offs) brings in analog design issues (analog view of digital design). • present use of small signal models in digital design are restricted to computing gains.Reliability problems such as electro migration, hot-carrier degradation and oxide break down. • Today’s class: • MOS small signal models: saturation, linear and cut-off regions • Example

  5. V GS2 C C GD DB V GS1 I D C C GS SB V DS SMALL SIGNAL MODEL Saturation Region • Instantaneous gate-to-source voltage • : DC bias, : small time-varying signal • Two small signal quantities: transconductance and output resistance. • : (small-signal) transconductance

  6. Saturation Region(contd..) • : output resistance

  7. C GD d g C DB V g V g V r gs m gs s sb ds C GS S C V SB sb b MOS small signal model in saturation and linear Saturation Region • Need to include body-effect if : • : (small-signal) transconductance due to body-bias

  8. Saturation Region(contd..)

  9. GATE SOURCE DRAIN (n+) (n+) CHANNEL SUBSTRATE(p-Si) Saturation Capacitances • Gate-to-source cap: • Gate-to-drain cap: • Source-to-bulk: (bias-dependent) • Drain-to-bulk: (bias-dependent)

  10. V GS2 C C GD DB V GS1 I D C C GS SB V DS SMALL SIGNAL MODEL g m Linear Region • : (small-signal) transconductance • As is small in linear region, hence can be assumed to be zero.

  11. Linear Region(contd..) • output resistance • Capacitances: • Gate-to-source/drain: • Source/drain-to-bulk: Same expression as in saturation.

  12. C GD d g C DB V gs C GS S C V SB sb b MOS small signal model in cut-off Cut-off Region • Infinite . Need to account for it if subthreshold conduction is non-trivial as in deep submicron technologies. • only capacitances remain. • Gate-to-source/drain: • Source/drain-to-bulk: Same expression as in saturation. • Gate-to-bulk:

  13. Quiz (in SWF)

  14. Example (in SWF)

  15. Summary • MOSFET small signal models: • saturation region: • linear region: • cut-off: and assuming subthreshold conduction is negligible. • Above small signal model parameters derived from long-channel equations. Not valid in deep submicron. Please continue for more examples

  16. Advanced Interactivity features in Flash • Flash, the tool used to generate the SWF files allows many advanced interactivity features • Many of these are either not possible in other tools or too difficult to implement or result in large file sizes. • Next few slides demonstrate some of these features

  17. Code explanations • Following two slides demonstrate animated description of sample Verilog and VHDL code • After the animated description, user enters the interactive mode and explore the code by rollover on highlighted regions • You can press the “End of the scene” button on the lower panel to skip animation and directly enter the rollover mode

  18. Hierarchical Diagrams • Flash is well known for designing innovative interactive user interfaces • In this example, the DSP block diagram can be explored hierarchically. • The ALU is used here to demonstrate this feature. Click on the blinking arrow

  19. Motorola DSP 56002

  20. Other innovative uses • Another nice feature allows user to drag and drop items and place them at the correct place. • In this example, this feature has been used to test user’s understanding

  21. Drag and Drop example

  22. Animation • Animations can be used to high-retention content. It makes concepts easier to grasp as well. • A very simplistic animation is presented here. (It has been taken from Java learning content and is used here just for illustration) • Use the Next button on the panel to play the animation in stages.

  23. End of Hybrid-Format presentation

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