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Lecture 8 Transistors

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  1. Lecture 8Transistors CSCE 211 Digital Design • Topics • Review: • Combinational Circuits • Decoders • Multiplexers • Breadboards, LEDs • Components on integrated circuit (ICs) • Transistors • CMOS • Readings 5.4, 5.7 September 29, 2014

  2. Hot Batteries • You should regularly check your batteries “slightly warm” is OK but hot indicates that your circuit has a short circuit. • Unplug quickly and check. • Look for direct lines Vcc to GND. • Remember you need 330 ohm resistors in series with LEDs and that includes segments of the seven segment display. • Recheck sections of the breadboard.

  3. Transistor: Water Flow Model Water flow in B raises the plunger so that water can flow from C to E. Small flow turns on and off bigger flow. Put signal on B, transfer signal C to E Reference: http://www.satcure-focus.com/tutor/page4.htm

  4. Transistor Terminology • Conductor – electrons easily passed from one atom to next (copper every atom has loose electron) • Insulator – electrons tightly tied down to atoms, no flow • Semiconductor – by adding impurities (doping) can be changed to increase conductivity • Silicon wafer – used for IC circuits • N-type - silicon doped with boron (excess electrons) • P-ype - silicon doped with phosphorous (excess “holes” lack of electrons)

  5. Transistor Reference: http://www.intel.com/education/transworks/

  6. Transistor Reference: http://www.intel.com/education/transworks/

  7. Transistor Put Positive charge on gate. This attracts electrons into gap. This allows electrons to pass freely through the gap. Reference: http://www.intel.com/education/transworks/

  8. Transistor Reference: http://www.intel.com/education/transworks/

  9. Transistor Take positive charge off Gate This stops attracting electrons. This shuts off the flow. Reference: http://www.intel.com/education/transworks/

  10. N channel transitor

  11. P channel Transistor

  12. CMOS Inverter

  13. CMOS NAND

  14. What’s This?

  15. High impedance • High impedance is the state of an output terminal which is not currently driven by the circuit; neither high nor low • Like an unconnected wire • It is also known as hi-Z, tri-stated, or floating http://en.wikipedia.org/wiki/High_impedance

  16. Tri-state Buffer In the tri-state buffer the enable input (B) acts as a switch Note if B is enabled then C=A and if B is not enabled then C = High-impedance http://en.wikipedia.org/wiki/Three-state_logic

  17. Tri-state Buffer Implementation • .

  18. Transmission Gates (Fig 3.45) A is the input; B the output

  19. 2-to-1 Mux from transmission gates • .