Analysis and Design of Analog Integrated Circuits UQSTC Diffusion Capacitance Positive bias:v +va 2kT I=Ag( W。 Dn)exp W kT IF is the diffusion current. 2019/9/3 UESTC Luo Ping 16
Analysis and Design of Analog Integrated Circuits 2019/9/3 UESTC Luo Ping 16 • Diffusion Capacitance 2 F D qI C kT 0 0 ( )exp p n n p D F p n D p D n qV I Aq W W kT IF is the diffusion current. Positive bias : D d v v
Analysis and Design of Analog Integrated Circuits Summary Characterized the reverse bias operation of the PN junction PN junction has a barrier potential o The breakdown voltage is proportional to Emax2 The PN junction depletion region acts like a voltage depen- dent capacitance Applications of the reverse biased PN junction Isolate transistor from the material they are built in Rectifier Variable capacitors Reference voltage source 2019/9/3 UESTC Luo Ping 17
Analysis and Design of Analog Integrated Circuits 2019/9/3 UESTC Luo Ping 17 Summary Characterized the reverse bias operation of the PN junction * PN junction has a barrier potential Ψo * The breakdown voltage is proportional to Emax 2 * The PN junction depletion region acts like a voltage dependent capacitance Applications of the reverse biased PN junction * Isolate transistor from the material they are built in * Rectifier * Variable capacitors * Reference voltage source
Analysis and Design of Analog Integrated Circuits 1.2 Large-Signal and Small-Signal Models of Bipolar Transistors 1.2.1 How the BJT works 1.Physical Aspects of a NPN BJT B Depletion Depletion B Region Region Depletion Depletion Region Region The emitter-base depletion region is generally smaller in width because the doping level is higher and base-emitter junction is generally forward-biased. 2019/9/3 UESTC Luo Ping 18
Analysis and Design of Analog Integrated Circuits 2019/9/3 UESTC Luo Ping 18 The emitter-base depletion region is generally smaller in width because the doping level is higher and base-emitter junction is generally forward-biased. 1. Physical Aspects of a NPN BJT 1.2.1 How the BJT works 1.2 Large-Signal and Small-Signal Models of Bipolar Transistors
Analysis and Design of Analog Integrated Circuits UsTC 2.Carrier Concentrations of the NPN BJT Carrier Pp(x)-np(x)=N Concenuat Depletion nnE Region nnC nn(Wa)=n,ea)≈ Depletion PncC PnE Emitter Collector.◆ X=0 x=WB ic =-inc =-(inE-inr)=-(iE-ipE-ipr) Assume the base-emitter junction is forward biased and the base-collector junction is reverse biased. 2019/9/3 UESTC Luo Ping 19
Analysis and Design of Analog Integrated Circuits 2019/9/3 UESTC Luo Ping 19 2. Carrier Concentrations of the NPN BJT Assume the base-emitter junction is forward biased and the base-collector junction is reverse biased. (0) exp( ) 0 T BE p p V v n n ( ) exp( ) 0 0 T BC p B p V v n W n N n (x) p (x) A p p p p NA p (x) n (x) ( ) ( ) C nC nE nr E pE pr i i i i i i i
Analysis and Design of Analog Integrated Circuits UOsTC 1.2.2 Large Signal Model of BJT 1.Large-signal models in the forward-active region ic=-inc=-(inE -inr)=-(iE -ipE -ipr) ”,(0)=nacp(）一nn（W,)="ep()=0 n(x) Jn=qD( =90,0 dx 4e 1,=94DB2=9 AD22 W: n=npoN WENA QB 2019/9/3 UESTC Luo Ping 20
Analysis and Design of Analog Integrated Circuits 2019/9/3 UESTC Luo Ping 20 (0) exp( ) 0 T BE p p V v n n ( ) 0 exp( ) 0 T BC p B p V v n W n ) ( ) ( dx dn x J qD p n n ) (0) ( B p n n W n J qD ) exp( ) (0) ( 0 T BE B n p B p C n V v W qAD n W n i qAD exp( ) T BE C S V v i I B n p S W qAD n I 0 i p NA n n 0 2 B n i B A n i S Q qAD n W N qAD n I 2 2 1.2.2 Large Signal Model of BJT ( ) ( ) C nC nE nr E pE pr i i i i i i i 1. Large-signal models in the forward-active region