MOS-Field Effect Transistors - Electronics II - Lecture Slides | EENG 3520, Study notes of Electronics

Download MOS-Field Effect Transistors - Electronics II - Lecture Slides | EENG 3520 and more Study notes Electronics in PDF only on Docsity! Dr. Shengli Fu Department of Electrical Engineering University of North Texas 1 EENG 3520: Electronics II Lecture 3 Dr. Shengli Fu Dr. Shengli Fu Department of Electrical Engineering University of North Texas 2 4. MOS Field-Effect Transistors 4.1 Physical Structure and Physical Operation Figure 4.1 Physical structure of the enhancement-type NMOS transistor: (a) perspective view; (b) cross-section. Typically L = 0.1 to 3 μm, W = 0.2 to 100 μm, and the thickness of the oxide layer (tox) is in the range of 2 to 50 nm. Dr. Shengli Fu Department of Electrical Engineering University of North Texas 5 5. Bipolar Junction Transistor 5.1 Physical Structure and Physical Operation Dr. Shengli Fu Department of Electrical Engineering University of North Texas 6 5. Bipolar Junction Transistor 5.1 Physical Structure and Physical Operation (cont.) Mode EBJ CBJ Cutoff Reverse Reverse Active Forward Reverse Reverse Active Reverse Forward Saturation Forward Forward BJT Modes of Operation > 0.5 V Dr. Shengli Fu Department of Electrical Engineering University of North Texas 7 5. Bipolar Junction Transistor 5.1 Physical Structure and Physical Operation (cont.) TBE VvSC B e Iii / ββ == BCE iii += TBETBE Vv S Vv SCE eIeIii // )/(11 α β β β β = + = + = α αβ β βα α − = + = = 1 1 EC ii Dr. Shengli Fu Department of Electrical Engineering University of North Texas 10 5. Bipolar Junction Transistor Assumption: • Only DC voltage are applied • |VBE| = 0.7 V (Active mode) • |VBE| = 0.7 V, |VCE| = 0.2 V (Saturation mode) Analysis Method: In which mode is the transistor operating? Assume one mode Determine voltage and current Check for consistency. Assume active mode, check vCB: > -0.4V (npn) < 0.4V (pnp) Assume saturation, IC/IB < β, or βforced < β 5.4 BJT Circuits at DC Dr. Shengli Fu Department of Electrical Engineering University of North Texas 11 5. Bipolar Junction Transistor Example 5.5: To determine the voltages at all nodes and the currents through all branches. Assume that the transistor β is specified to be at least 50. 1. Assume active: VBE = 0.7V, VE = 6 – 0.7 = 5.3 V 2. IE = 5.3 / 3.3 = 1.6mA 3. IC = αIE = (50/51)IE ≅ 1.6 mA 4. VC = 10 – 1.6 x 4.7 = 2.48 V < VB 1. Assume saturation: VBE = 0.7V, VE = 6 – 0.7 = 5.3 V 2. IE = 5.3 / 3.3 = 1.6mA 3. VCE = 0.2 V, VC = VE + VCE = 5.3 + 0.2 = 5.5 V 4. IC = (10 – 5.5) / 4.7 = 0.96 mA 5. IB = IE – IC = 1.6 – 0.96 = 0.64 mA 6. βforced = IC / IB = 0.96 / 0.64 = 1.5 < 50 Dr. Shengli Fu Department of Electrical Engineering University of North Texas 12 5. Bipolar Junction Transistor 5.5 Biasing in BJT Amplifier Circuits Goals: To establish a constant dc current IC in the collector of the BJT • Insensitive to variations in temperature and to the large variations in the value of β • To allow for maximum output signal swing Two obvious Examples: TBE VV SC eII /= Small VBE, Large IC BCCB RVI /)7.0( −≅ IC depends on β Dr. Shengli Fu Department of Electrical Engineering University of North Texas 15 5. Bipolar Junction Transistor Figure 5.47 (a) A BJT biased using a constant-current source I. (b) Circuit for implementing the current source I. R VVVI BEEECCREF −−− = )( SAME VBE R VVVII BEEECCREF −+ == CURRENT MIRROR 5.5 Biasing in BJT Amplifier Circuits (cont.) Dr. Shengli Fu Department of Electrical Engineering University of North Texas 16 5. Bipolar Junction Transistor 5.6.1 Small Signal Models Dr. Shengli Fu Department of Electrical Engineering University of North Texas 17 5. Bipolar Junction Transistor 5.6.1 Small Signal Models (cont.)