DIOD E AND ITS APPLI AT C I O N: T h diod is a p-t p, y intin s ic, n-typ diod consis ting of a naow lay of p- typ smiconducto and a naow lay of n-typ smiconducto, wi th a thick gion of intins ic o b twn thm. vy lightly n-dopd smiconduct o matial sandwic hd S ilicon th smicon ducto nomally usd capability i t off s h igh sistivly th b caus of i ts pow handling tinsic gion. B ut, now Gallium Asnid ( Ga A s) al so b ing u sd. M tal lay s a attach d puposs. It s m ain applica t ions a micowav switching modul ation. -a-days contact diod acts as a mo o MHz. w ith a n lss odinay at f quncis up to about 100 A t hi gh fqunc i s, i t cass t o ctify n acts a s a vaiab l sistanc quiv alnt c icuit a sistanc-voltag chaactis tics. In ' th q uivalnt c i cuit, Land C psn t packag inductanc capac itanc p p spctivly. R is th b ulk smic onducto lay psnt spctiv j unction sistanc Wh n th b ias vaid o n th f om a typica l v alu of 6 K u nd J co ntact sista n c. R. an d C. capacitan c of tinsic lay., its micowav si stanc. R changs
n gativ b ias to phap s 5 Q mou ntd ac oss a 50 Q co-a xial l, i t whn bias no t back-bia s d, so t hat p ow fl ow wi ll not b p ositiv. Th u s, if signif cant i ly lo ad this intf d wit. now wad b iasd, i ts sis tanc do ps significantly t o 5Q, s o of p ow fl ctd hadly any is tans m ittd; th switch. l in wh n i t h H o wv, if th t hat mos t is a cting a s a APPLICATION O F DIODE AS SING LE POL E SWITCH: A can b u sd ith a si singl-p ol, singl-thow RF switch. Th s ci cuits a show n blow. s o a sh unt confi guation t o m a w ith b ias nt woks
I n is s confi guation s witch O N w hn l f o wad iasd B O FF w hn i t vs b iasd. B ut, shu nt confi guation of w ad b iasing th diod " cuts-o ff' th tansmissio n f om inpu t t o tansmission and vs biasing th outpu t. i mpdanc at RF opa ting fquncy and RF h igh R F impdanc. T h DC b locks sh ould hav a c hok inducto diod nsus vy low s shou ld h av v y Idall y, a at tnuation s witch shoul d hav z o ins tion l oss O N stat inf it OFF s tat. Ra listic switch ing lm n ts, of co u s, sul t som instion l oss ON s tat an d fit a ttnuation OFF stat d u t o non-z o wad bias sistanc. Similal y, vs bi as s hunt capa cito no t infit & non-z o stion los s sults. Bcaus of lag bakdown vol tag ( = 500 volt s ) compa d t o odinay, dio d c an b bias d at hig h ngativ gio n so t s ignal, supimpos d on d. c. cannot m ak th dvic wad bias d. h at a n lag a. c.
Fowa d B ias: Whn diod f o wad i b a s d, capacito s C C. a lmost b hav a s op n c icuits s o t hat quivaln t ci cuit can now b simplifi d w h Rf ot t al wad sista nc of g ivn.. T h diod impdanc Z d of diod g ivn R vs b ias: W hn tinsic lay C. bco ms signifi cant and R v s b iasd, capacitanc of b quiva lnt vs sistanc simplifi d quivalnt cicuit vs b iasd can b co nstuctd as show n. T h impdanc Z d of diod und vs b i as, thn g ivn R vs b ias: W hn tinsic lay C. bco ms significan t and v s b iasd, capacitanc of R b quiva lnt vs sistanc simplifi d quivalnt cicuit vs b iasd can b co nstuctd ; T h impdanc Z d of diod und vs b i as, thn g ivn