Qbc bjt c ib bfib qbe excess carriers in base plus

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Unformatted text preview: iD qSB qG: Gate charge; a function of vGS, MOSFET: n-channel B vDS, and vBS. qDB: D-B junction depletion charge qSB: S-B junction depletion charge Lecture 13 - Slide 6 Clif Fonstad, 10/03 (exaggerated for impact) iC The Early Effect: BJT: npn -1/l = -V A 0.2 V vCE iD MOSFET: n-channel vDS Clif Fonstad, 10/03 -1/l = -V A Lecture 13 - Slide 7 Active Length Modulation - the Early Effect: MOSFET MOSFET: We begin by recognizing that the channel length decreases with increasing vDS and writing this dependence to first order in vDS: L Lo(1 lvDS) and 1/L (1 + lvDS)/Lo K = (W/L) e Cox* Inserting the channel length variation with vDS into K we have: K Ko (1 + lvDS) where K (W/Lo) e Cox* Thus, in saturation: iD Ko (vGS VT)2 (1 + lvDS)/2a Clif Fonstad, 10/03 Lecture 13 - Slide 8 Active Length Modulation - the Early Effect: BJT BJT: We begin by recognizing that the base width decreases with increasing vCE and writing this dependence to first order in vCE: wB* wBo*(1 lvCE) and 1/wB* (1 + lvCE)/wBo* Then we note that in a modern BJT the emitter defect is the more important factor: bF = (1 dB)/(dE + dB) 1/dE = (De/Dh)(NDE/NAB)(wE*/wB*) Inserting the base width variation with vCE into bF we have: bF bFo(1 + lvCE) where bFo (De/Dh)(NDE/NAB)(wE*/wBo*) Thus, in the F.A.R.: iC bFo(1 + lvCE)iB Clif Fonstad, 10/03 Lecture 13 - Slide 9 Output Characteristics Saturation iC BJT: npn Forward Active Region iC bF iB iC bF(1 + lvCE)iB Cutoff vCE 0.2 V MOSFET: Linear iD or...
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This note was uploaded on 07/20/2009 for the course CSAIL 6.012 taught by Professor Prof.cliftonfonstadjr. during the Fall '03 term at MIT.

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