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Small Signal Model MOS Field-Effect Transistors (MOSFETs)

Small Signal Model MOS Field-Effect Transistors (MOSFETs). 1. Quiz No 3 DE 27 (CE). 20-03-07. R out. Draw small signal model (4) Find expression for R out (2) Prove v o /v sig = ( β 1 α 2 R C )/(R sig +r π ) (4).

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Small Signal Model MOS Field-Effect Transistors (MOSFETs)

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  1. Small Signal Model MOS Field-Effect Transistors (MOSFETs) 1

  2. Quiz No 3 DE 27 (CE) 20-03-07 Rout. • Draw small signal model (4) • Find expression for Rout(2) • Prove vo/vsig = (β1α2RC)/(Rsig+rπ)(4).

  3. A traveler once came to the mosque to see the prophet.After greeting the prophet he was asked where he was from. The traveler replied that he came from very farjust to get a few questions answered. Following is thedialogue between the traveler and the prophet.Traveler: I do not want adhaab to be written in my account. Prophet: behave well with your parentsTraveler: I want to be known amongst people as anintelligent person. Prophet: fear Allah always.Traveler: I want to be counted amongst Allah's favorites.Prophet: recite Quran every morning and evening. Traveler: I want my heart to always be enlightened.(roshan and munawer) Prophet: never forget death

  4. Traveler: I never want to be away from Allah's blessing. Prophet: always treat fellow creatures well.Traveler: I never want to be harmed by my enemies. Prophet: always have faith in only Allah.Traveler: I never want to be humiliated. Prophet: becareful of your actions.Traveler: I wish to live long. Prophet: always do sila-rahm. (Goodness towards blood relations)Traveler: I want my sustenance to increase. Prophet: always be in wudhoo.Traveler: I wish to stay free of adhaab in the grave.Prophet: always wear pure (paak) clothes. Traveler: I never want to burn in hell.Prophet: control your eyes and tongue.

  5. Traveler: how do I get my sins forgiven? Prophet: always ask forgiveness from Allah with a lot of humility.Traveler: I want people to respect me always. Prophet: never extend your hands of need at people.Traveler: I want to always be honored. Prophet: never humiliate or put down anyone.Traveler: I don't want to be squeezed by fishare qabr.(Squeezing in the grave) Prophet: recite sura e mulk often.Traveler: I want my wealth to increase. Prophet: recite sura e waqia every night.Traveler: I want to be safe and at peace on day of judgment. Prophet: do zikr of Allah from dusk to night.Traveler: I want to be in full attention and concentration during namaaz. Prophet: always do wudhoo with concentration and attention

  6. Enhancement-type NMOS transistor:

  7. Figure 4.2 The enhancement-type NMOS transistor with a positive voltage applied to the gate. An n channel is induced at the top of the substrate beneath the gate.

  8. Enhancement-type NMOS transistor:

  9. MOSFET Analysis iD = iS, iG = 0

  10. Large-signal equivalent-circuit model of an n-channel MOSFET : Operating in the saturation region.

  11. Large-signal equivalent-circuit model of an p-channel MOSFET : Operating in the saturation region.

  12. Large Signal Model : MOSFET

  13. Transfer characteristic of an amplifier

  14. Conceptual circuit utilized to study the operation of the MOSFET as a small-signal amplifier. The DC BIAS POINT To Ensure Saturation-region Operation

  15. Signal Current in Drain Terminal

  16. Total instantaneous voltages vGSand vD

  17. Small-signal ‘π’ models for the MOSFET

  18. Common Source amplifier circuit Example 4-10

  19. Small Signal ‘T’ Model : NMOSFET

  20. Small Signal Models ‘T’ Model

  21. Single Stage MOS Amplifier

  22. Amplifiers Configurations

  23. Common Source Amplifier (CS) :Configuration

  24. Common Source Amplifier (CS) • Most widely used • Signal ground or an ac earth is at the source through a bypass capacitor • Not to disturb dc bias current & voltagescoupling capacitors are used to pass the signal voltages to the input terminal of the amplifier or to the Load Resistance • CS circuit is unilateral – • Rin does not depend on RL and vice versa

  25. Small Signal Hybrid “π” Model (CS)

  26. Small Signal Hybrid “π” Model : (CS)

  27. Small-signal analysis performed directly on the amplifier circuit with the MOSFET model implicitly utilized.

  28. Common Source Amplifier (CS) Summary • Input Resistance is infinite (Ri=∞) • Output Resistance = RD • Voltage Gain is substantial

  29. Common-source amplifier with a resistance RSin the source lead

  30. The Common Source Amplifier with a Source Resistance • The ‘T’ Model is preferred, whenever a resistance is connected to the source terminal. • ro(output resistance due to Early Effect) is not included, as it would make the amplifier non unilateral & effect of using ro in model would be studied in Chapter ‘6’

  31. Small-signal equivalent circuit with ro neglected.

  32. Small-signal Analysis.

  33. Voltage Gain : CS with RS

  34. Common Source Configuration with Rs • Rs causes a negative feedback thus improving the stability of drain current of the circuit but at the cost of voltage gain • Rs reduces id by the factor • (1+gmRs) = Amount of feedback • Rs is called Source degeneration resistance as it reduces the gain

  35. Small-signal equivalent circuit directly on Circuit

  36. A common-gate amplifier based on the circuit

  37. Common Gate (CG) Amplifier • The input signal is applied to the source • Output is taken from the drain • The gate is formed as a common input & output port. • ‘T’ Model is more Convenient • ro is neglected

  38. A small-signal equivalent circuit

  39. A small-signal Analusis : CG

  40. A small-signal Analusis : CG

  41. Small signal analysis directly on circuit

  42. The common-gate amplifier fed with a current-signal input.

  43. Summary : CG • 4. CG has much higher output Resistance • CG is unity current Gain amplifier or a Current Buffer • CG has superior High Frequency Response.

  44. A common-drain or source-follower amplifier.

  45. Small-signal equivalent-circuit model

  46. Small-signal Analysis : CD

  47. (a) A common-drain or source-follower amplifier :output resistance Rout of the source follower.

  48. (a) A common-drain or source-follower amplifier. : Small-signal analysis performed directly on the circuit.

  49. Common Source Circuit (CS)

  50. Common Source Circuit (CS) With RS

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