ECE 145A / 218 C, notes set 3: Two-Port Parameters

Transcription

1 class notes, M. odwell, copyrihted 9-4 ECE 45A / 8 C, notes set 3: Two-Port Parameters Mark odwell University of California, anta Barbara rodwell@ece.ucsb.edu , fax

2 Device Descriptions for Circuit Desin class notes, M. odwell, copyrihted 9-4 Equivalent - circuit model physically based cludes dependence upon DC bias & frequency often cludes device size dependence weakness : necessary simplified, hence some errors - Port Model matrix of tabular data need one model for each bias pot,each frequency hue data sets required. medium for both (a) measured data and (b) E/M simulation data - port methods also useful for eneral network theory.

3 HBT equivalent-circuit model class notes, M. odwell, copyrihted 9-4 be / m f f b base c collector B bb C cbx C cbi c C mo I C BE IC ( nkt / q) be be m be e - c m mo e c (typically~.8) C be,diff = m f C e ex E We will cover this more detail soon

4 FET Equivalent-Circuit Model class notes, M. odwell, copyrihted 9-4 We will cover this more detail soon G D D D G i C d m s G ds d D W C s s C db G C sb s C k m o C G d s ds i v T eq k o eq NW ~ / W m eff NW or NW (.3.5)fF/ m T NW k T o eq W C C d s sb db s / NW NW NW th ~ s W N / NW N end G i C s Increase f max us - short ate fers - ample substratecontacts C d s s m s C sb G ds D C db

5 class notes, M. odwell, copyrihted 9-4 -Port Descriptions ( 3-Wire Network or Device) Box miht conta : a transistor, a passiveelement, a subcircuit The termal characteri stics relate the variables,, I, and I. There are derees of freedom. Any twovariables can be set as the* dependent variables*. The rema two variables, the* dependent variables*, can then be writtenas functions of the dependent variables.

6 class notes, M. odwell, copyrihted 9-4 Two-Port Parameters: epresent Device or Network

7 class notes, M. odwell, copyrihted 9-4 Admittance Parameters ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( Y Y Y Y I I etc., e ) (, e ) ( Frequency - doma description : t t e I t i e t v taken as implicit. is DC bias voltaes. written as functions of Currents are

8 class notes, M. odwell, copyrihted 9-4 Admittance Parameters Example: imple FET Model I I Y Y Y Y By spection: Y s d d Y i ( C C ) m C d G ds C C d

9 Impedance Parameters class notes, M. odwell, copyrihted 9-4 I I oltaes are writtenas functions of currents. Example : By spection: 3 3 i easy!

10 Hybrid Parameters: Old and Obscure class notes, M. odwell, copyrihted 9-4 I h h h h I This is certaly an odd choice of dependent variables.

11 Hybrid Parameter Example: imple BJT Model class notes, M. odwell, copyrihted 9-4 I note: h h m be h h I / be be ~ I b By spection: / H C C be be be be ce This is related toshort - circuit current a.

12 hort-circuit Current Ga class notes, M. odwell, copyrihted 9-4 short - circuit current a I I I I put short-circuited. I I put short-circuited h f frequency at which h * extrapolates * to. "short - circuit current - a cutoff frequency". For thehihly simplified model on the prior pae, if, f m / C be.

13 Defition of -parameters... with a's and b's class notes, M. odwell, copyrihted 9-4 amplifier - parameters are riorously defed terms of the wave amplitudes on transmission les connected to the device under test b a b a...where thea' s and b's are the wave amplitudes. : a / and b /

14 class notes, M. odwell, copyrihted 9-4 Defition of -parameters... with +'s and -'s amplifier We can also write " " waves travel towards the - port;"-" waves travel away.

15 De-Mystify -Parameters class notes, M. odwell, copyrihted 9-4 At port, and I At port, and I If ( Y we know therelationship between [ I or parameters), wecan calculate ( parameters)., I the relationship between [ ] and [,, ]: ] and [, ]:

16 How to Compute -parameters quickly: class notes, M. odwell, copyrihted 9-4 If then, hence Now Def, so as theput impedance iven,

17 class notes, M. odwell, copyrihted 9-4 Input impedance = Input eflection Coefficient Not that Note that reflection coefficien t ( of specifyput impedance. ) is a method iven reflection coefficien t is theput impedance reflection coefficien t that theload is impedance.

18 class notes, M. odwell, copyrihted 9-4 Output impedance = Output eflection Coefficient The same analysis & comments clearly applies to. By symmetry, Note that reflection coefficien t ( of specificy put impedance. en en ) is a method iven en reflection coefficien t is the put impedance that theenerator reflection coefficien t is impedance.

19 Comput : Example class notes, M. odwell, copyrihted 9-4 Given 5, what is? 54 o by similar aruments, /4 4 4

20 class notes, M. odwell, copyrihted 9-4 Comput. / hence /, ) /( and we have Given en s en s en s s en T T : et en - hence, we have Given en en en en ) / ( o

21 elat amplifier Gas to -parameters class notes, M. odwell, copyrihted 9-4 These relationships allow us todevelop a simpler way of fd the - parameters : v v en enerator load..which is simply **how much bier * thesinal became upon* sertion * of the amplifier the5 Ohm system. is called the* sertion a *.

22 elat amplifier Gas to -parameters class notes, M. odwell, copyrihted 9-4 en=o =o en By symmetry v v en enerator load

23 class notes, M. odwell, copyrihted 9-4 elat amplifier Gas to -parameters and en=o =o en and can be directly related toput and put impedances / / / / tells us the... practice, we do not need to plu to the formulas : know the by themith chart, where, where load enerator, becuase the formula is one - to-one and is neatly represented

24 class notes, M. odwell, copyrihted 9-4 elat amplifier Gas to -parameters and (,) (,) and / / / /, where, where wedo not need to plu to the formulas : themith chart is a plot of this formula, so the mith chart plots i at thesame time load enerator freq (.GHz to.ghz)

25 Example of work with -parameters class notes, M. odwell, copyrihted 9-4 en=o C =o m en...easy!!! mo C / / / / o,, where where / C fity

26 class notes, M. odwell, copyrihted 9-4 Example of work with -parameters etc ", " the importance of...this illustrates where, / / where, / / / / / o o o o o C C C C C C C en=o =o en C

27 db((,)) Why do we care ab impedances matched to 5 Ohms? class notes, M. odwell, copyrihted tand ripplesof waves on transmission les theform exp( f ) cause a/phase must have short transmission les, or theles must be well - termated freq, GHz. Either we