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Understanding CMOS Inverter Characteristics and Transistor Operations in VLSI Design

This lecture by Prof. Sherief Reda from Brown University focuses on the design and implementation of VLSI systems, specifically the operation of NMOS and PMOS transistors. It explores DC transfer characteristics based on varying input voltages (Vin) and how altering PMOS width affects inverter performance, including noise margins. The discussion encompasses ideal and non-ideal transistor characteristics, inverter DC transfer characteristics, and practical simulation aspects with SPICE and L-Edit software, providing insights into effective VLSI design and analysis.

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Understanding CMOS Inverter Characteristics and Transistor Operations in VLSI Design

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  1. Design and Implementation of VLSI Systems (EN1600) lecture09 Prof. Sherief Reda Division of Engineering, Brown University Spring 2008 [sources: Weste/Addison Wesley – Rabaey/Pearson]

  2. Summary of transistor operation NMOS transistor PMOS transistor

  3. DC transfer characteristics

  4. Vin = 0 PMOS on (linear), NMOS off

  5. PMOS on (linear), NMOS on (saturation) • Vin = 0.2VDD

  6. PMOS on (linear ~ sat) and NMOS (sat) • Vin = 0.4VDD

  7. Vin = 0.6VDD PMOS on (sat) NMOS on (linear)

  8. Vin = 0.8VDD PMOS on (off ~ linear) and NMOS on (linear)

  9. Vin = VDD NMOS on (linear) and PMOS cut off

  10. Summary of voltage transfer function A B C E D

  11. Noise margins

  12. desired regions of operation CMOS inverter noise margins

  13. V V V in3 in3 in3 V in V out What is the impact of altering the PMOS width in comparison to the NMOS width on the DC char? I , | I | dsn dsp V in3 V V DD out If we increase (decrease) the width of PMOS compared to NMOS  for the same input voltage, a higher (lower) output voltage is obtained

  14. Impact of skewing transistor sizes on inverter noise margins • Increasing (decreasing) PMOS width to NMOS width increases (decreases) the low noise margin and decreases (increases) the high noise margin

  15. Pass transistor DC characteristics • As the source can rise to within a threshold voltage of the gate, the output of several transistors in series is no more degraded than that of a single transistor

  16. Summary • Ideal transistor characteristics • Non-ideal transistor characteristics • Inverter DC transfer characteristics • Simulation with SPICE and integration with L-Edit

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