tailieunhanh - Bài giảng Thiết kế vi mạch số: Chương 2 - TS. Trương Quang Vinh

Bài giảng "Thiết kế vi mạch số - TS. Trương Quang Vinh" gồm các nội dung sau: Vận hành bóng bán dẫn, đặc điểm I-V, đặc điểm C-V, đặc điểm chuyển DC và một số nội dung khác. | Lecture 2: MOS Transistor Theory 1. 2. 3. 4. MOS transistor operation I-V characteristics C-V characteristics DC transfer characteristics 2: MOS Transistor Theory 1 1. MOS Transistor Operation So far, we have treated transistors as ideal switches An ON transistor passes a finite amount of current – Depends on terminal voltages – Derive current-voltage (I-V) relationships Transistor gate, source, drain all have capacitance – I = C (∆V/∆t) -> ∆t = (C/I) ∆V – Capacitance and current determine speed 2: MOS Transistor Theory CMOS VLSI Design 4th Ed. 2 1 MOS Capacitor Gate and body form MOS capacitor V Vt + - g s + - Vgd = Vgs d n+ Vds = 0 n+ p-type body b Vgs > Vt + - g s + - d n+ n+ Vgs > Vgd > Vt Ids 0 Vt g + - + - Vgd Vgs-Vt p-type body b 2: MOS Transistor Theory CMOS VLSI Design 4th Ed. 7 2. I-V Characteristics In Linear region, Ids depends on – How much charge is in the channel? – How fast is the charge moving? 2: MOS Transistor Theory CMOS VLSI Design 4th Ed. 8 4 Channel Charge MOS structure looks like parallel plate capacitor while operating in inversions – Gate – oxide – channel Qchannel = CV Cox = εox / tox C = Cg = εoxWL/tox = CoxWL V = Vgc – Vt = (Vgs – Vds/2) – Vt polysilicon gate W tox n+ L n+ SiO2 gate oxide (good insulator, εox = ) gate Vg + + Vgs Cg Vgd drain source Vs Vd channel + n+ n+ Vds p-type body p-type body 2: MOS Transistor Theory CMOS VLSI Design 4th Ed. 9 Carrier velocity Charge is carried by eElectrons are propelled by the lateral electric field between source and drain – E = Vds/L Carrier velocity v proportional to lateral E-field – v = µE µ called mobility Time for carrier to cross channel: – t=L/v 2: MOS Transistor Theory CMOS VLSI Design 4th .