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4 bit Versatile CMOS Rate Multiplier

4 bit Versatile CMOS Rate Multiplier

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4 bit Versatile CMOS Rate Multiplier

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  1. 4 bit Versatile CMOS Rate Multiplier Hardik Parikh Akshay Bhat Alex Jose Swastick Biswas Advisor: Dave Parent DATE: 05/11/2005

  2. Agenda • Abstract • Introduction • What is a Rate Multiplier and applications • Cumulative adder Principle • Improvements made to make the circuit versatile • Project Highlight • Project Details • Results • Cost Analysis • Conclusion

  3. Abstract We designed a 4-bit rate multiplier that operates at 200 MHz and uses 18.9mW of Power and occupies an area of 380 x 200 mm2

  4. Introduction • Rate Multiplier: A digital circuit that multiplies the incoming clock by a ratio to give an output pulse rate: where, P and Q are integers and P < Q This is not a frequency divider as numerator P is not one • Application: * Arithmetic & Mathematic Functional generation * PCM systems * Motor Control Systems * Vector Generation & Interpolation * Frequency Synthesizer

  5. Introduction Clock Reset P (Clock) D Register Q Full Adder Capacity = Q Cumulative Adder Principle P

  6. Introduction Clock Reset P (Clock) 4bitD Register Q c_out 4 bit Adder (CLA) D select 4 bit Multiplexer (2:1) 24 – Q + P Adder (CLA) Cin = 1 P 1’s Complement Q

  7. Project highlight • Programmable rates that broaden the application area considerably • High speed implementation through Carry look ahead adders • Optimally spaced output pulse distribution • Cascadable in multipliers of 4 bits • Most of the standard industry chips are BCD rate multipliers. This rate multiplier is more versatile as the denominator Q is programmable.

  8. Project Details Functional Verification Architecture Style Sizing, Schematics, Simulation Floor Planning Layout & Verification Post extraction simulation

  9. Architecture Style Option 1: Standard AOI

  10. Architecture Style Example: Carry out c4 = G3 + P3G2 + P3P2G1 + P3P2P1G0 + P3P2P1P0C0 Option 2: Using minimum transistors

  11. Architecture Style Option 3: Combination of AOI and Boolean Gates.

  12. Longest Path Calculation Clock Reset P (Clock) 4bitD Register Q 4 bit Adder (CLA) D 4 bit Multiplexer (2:1) Assuming that P and Q do not change Adder (CLA) Cin = 1 P 1’s Complement Q

  13. Longest Path Calculations TP = 5 nsec / 9 = 0.555 n sec

  14. Schematic

  15. And D ff (input) CLA 1 Mux CLA 2 D ff (input) CLA 1 Mux CLA 2 CLA 1 Mux CLA 2 D ff (input) D ff (input) CLA 1 Mux CLA 2 D ff (input) D ff (Register) D ff (Register) D ff (input) Floor Plan D ff (input) D ff (Register) D ff (Register) D ff (Sync.) D ff (input)

  16. Layout • Features: • Vdd and Ground lines interleaved to save area • Efficient routing and negligible empty space • Approximately squarish. The 4 hours spent on floor planning was worth it!

  17. Verification net-lists match !

  18. Simulation 1

  19. Simulation 2

  20. Power Analysis

  21. Cost Analysis • Time spent on each phase of the project in man hours • Verifying logic: 10 • Schematic, sizing and verifying timing: 40 • Layout: 140 • Post extracted timing: 5

  22. Lessons Learned • Have a rough idea of DRC rules before sizing the transistors. We underestimated the DRC minimum metal spacing only to find that the design became too tight. • Before starting layout spend time on making a floor plan • Document your design • Using Cell based design makes life easy! It reduces debug time • Time management is the key between success and failure!

  23. Summary • This project gave us a good overview of Digital CMOS Circuit Design. • Rate-multipliers can be used for low power frequency synthesizers.

  24. Acknowledgements • Thanks to Cadence Design Systems for the VLSI lab • Thanks to Professor Dr. Parent for his timely advice.