121B_1_bjt

Base emitter depletion charge qbf aq wb 0 ndx is the

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: harges induced in the base are the electrons in the depletion region, the other half being imaged in the collector. i.e., QBimg I c xc 2 sat Jason Woo QBimg VBE qI C xc = kT 2 sat EE121B Spring 2010 49 Similarly, C b c = Q B is the depletion capacitance of the base-collector junction VBC i rb c = bc vbc is due to the reversed biased base-collector junction current Also gm vb e = ic ic 1 gm = * ib rbe * with vbe = ib rbe Recall ic = * ib VA ro = IC VCB is the Early effect factor: = 1 + VA Also: Jason Woo and VA is the Early voltage 50 EE121B Spring 2010 Finally, if we ac ground the collector terminal (tie to the ac emitter). ic gm rbe h fe = = ib qI c qI c xc 1 + j rbe C bedep + + C b c B + kT kT 2 sat That is, the cut-off frequency for current gain, fT, ic (T ) T =1 fT = with ib (T ) 2 can be derived to be: rbe xc 1 C bedep + C b c + B + EC = 2 fT gm rb e 2 sat ( ) In the case where there is other parasitic capacitance, Cp, between the base-collector and the base-emitter junctions xc 1 kT C b edep + C bc + C p + B + = 2 f...
View Full Document

{[ snackBarMessage ]}

Ask a homework question - tutors are online