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Transcript
Small Signal Model MOS Field-Effect Transistors (MOSFETs) 1 Quiz No 3 DE 27 (CE) 20-03-07 Rout. (a) (b) (c) Draw small signal model (4) Find expression for Rout (2) Prove vo/vsig = (β1α2RC)/(Rsig+rπ) (4). 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 far just to get a few questions answered. Following is the dialogue between the traveler and the prophet. Traveler: I do not want adhaab to be written in my account. Prophet: behave well with your parents Traveler: I want to be known amongst people as an intelligent 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 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. 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 Enhancement-type NMOS transistor: 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. Enhancement-type NMOS transistor: MOSFET Analysis iD = iS, iG = 0 Large-signal equivalent-circuit model of an n-channel MOSFET : Operating in the saturation region. Large-signal equivalent-circuit model of an p-channel MOSFET : Operating in the saturation region. Large Signal Model : MOSFET Transfer characteristic of an amplifier Conceptual circuit utilized to study the operation of the MOSFET as a small-signal amplifier. The DC BIAS POINT To Ensure Saturation-region Operation Signal Current in Drain Terminal Total instantaneous voltages vGS and vD Small-signal ‘π’ models for the MOSFE Common Source amplifier circuit Example 4-10 Small Signal ‘T’ Model : NMOSFET Small Signal Models ‘T’ Model Single Stage MOS Amplifier Amplifiers Configurations Common Source Amplifier (CS) :Configuration 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 & voltages coupling 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 Small Signal Hybrid “π” Model (CS) Small Signal Hybrid “π” Model : (CS) Rin RG R o ro || RD vo vo v gs Gv vsig v gs vsig RG v gs vsig RG Rsig vo g m v gs ro || RD || RL RG vo Gv g m ro || RD || RL v gs RG Rsig Small-signal analysis performed directly on the amplifier circuit with the MOSFET model implicitly utilized. Rin RG R o ro || RD RG vo g m ro || RD || RL v gs RG Rsig Common Source Amplifier (CS) Summary • Input Resistance is infinite (Ri=∞) Rin RG • Output Resistance = RD R o ro || RD • Voltage Gain is substantial RG vo g m ro || RD || RL R R v gs sig G Common-source amplifier with a resistance RS in the source lead 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’ Small-signal equivalent circuit with ro neglected. i vg 1 RS gm Small-signal Analysis. Rin RG Ro RD Voltage Gain : CS with RS vo vo vgs vi Gv vsig vgs vi vsig vo g m v gs RD || RL 1 gm vi v gs vi 1 1 g m RS RS gm RG vi vsig RG Rsig RG g m RD || RL vo Gv vsig RG Rsig 1 g m RS 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 Small-signal equivalent circuit directly on Circuit A common-gate amplifier based on the circuit 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 A small-signal equivalent circuit A small-signal Analusis : CG vi vi 1 Rin ii g m vi g m Rout RD A small-signal Analusis : CG Gv vo v v o i vsig vi vsig vo g m vi RD || RL 1 gm vsig Rin vi vsig vsig 1 Rin Rsig 1 g m Rsig Rsig gm Gv vo g R || RL m D vsig 1 g m Rsig Small signal analysis directly on circuit The common-gate amplifier fed with a current-signal input. Summary : CG 4. CG has much higher output Resistance 5. CG is unity current Gain amplifier or a Current Buffer 6. CG has superior High Frequency Response. A common-drain or source-follower amplifier. Small-signal equivalent-circuit model Small-signal Analysis : CD (a) A common-drain or source-follower amplifier :output resistance Rout of the source follower. Rout 1 1 ro || gm gm (a) A common-drain or source-follower amplifier. : Smallsignal analysis performed directly on the circuit. Common Source Circuit (CS) Common Source Circuit (CS) With RS Common Gate Circuit (CG) Current Follower Common Drain Circuit (CD) Source Follower Summary & Comparison Small Signal Model Small Signal Model VBE=0.7 V β =200 K’n(W/L)=2mA/V2 Vt=1V Figure P6.123 DC Analysis Figure P6.123