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這是小弟寫的文章 編講義用的 歡迎高手同行找碴:1 }# w! z" Q' Q3 W8 c: Z" i
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This section highlights the importance of an accurate pre-determined DC compact model.\cite{dc!!!}8 m. A D4 b: F/ e# {
For compact model developers, extraction of the DC parameters always needs to be carried out before the extraction of AC ones.
! g% k$ C" {, eFor devices measurement, DC measurement has to be carried out before AC measurement.! L# b' g2 z/ l6 A [7 `6 A" \8 {
For modern IC designers, DC analysis needs to be carried out before AC analysis.\cite[4.6.4]{smith!}
$ Q% L7 L, M# k% t) GFor SPICE-like simulators, DC simulation also needs to be swept first and then follows by AC simulation.\cite{nlz!}
" `; F1 o8 R" C* G: V- [2 oFrom the device-level perspectives,
, T- P' L& y! s% _a set of equations which describe the terminal characteristics of DUT are written in a compact model." r( A8 K$ w( T* l9 t0 e
The equations are solved by SPICE-like simulators.0 \. f( Y, V+ ^' v9 ~6 K7 {
The procedure of establishing equations, describing device's electrical characteristics, in a compact model0 M4 L. n2 F+ ?; H. I0 C
and have them solved by SPICE-like simulators is termed as: Device Characterization.; @, }0 e+ T- @+ |8 i- c' H
The fully Characterizations are treated by two independent steps:1 m' y" m3 p$ D* O' T, p
(1)DC Characterization or DC parameters extraction# Z( d" b) e2 Z$ K# R8 I7 _& t( v( p% u8 r
(2)AC Characterization or AC parameters extraction5 n8 t$ r' a( _. K
Characterizing a nonlinear electronics component always begins with
3 \. y2 K$ Q) X: l, J8 IDC characterization and follows by the AC characterization.
+ a7 r* k& i6 H% x1 o% w3 lBecause the AC model is origined from the linearization of the DC model at an indicated operating point.
1 N) H$ K! a- L8 W9 ~' z9 a8 N5 \6 rAccordingly, accuracy is highly required in DC characterization because of its piority in the procedure of parameter extraction .
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' V- _2 Y2 v, \; o- P; W7 cFrom the circuit-level perspectives,,- k+ E6 x6 \2 k! y' A
Circuit analysis refers to solving a circuit with KVL and KCL.
6 n5 K5 J1 J6 B) w, G( TTo be more specific, it means solving out nodes voltages and branches currents of each element in a circuit.1 T, g) g7 S. `* T( V0 Q
As the source of stimulus can be systematically separated into DC sources and AC sources,$ O4 w* ^+ }3 \1 ~# k' d7 m8 F
the unknown/solutions of the circuit are also separated into DC part and AC part.; n/ \0 ^7 L M# T. B
Analyzing a circuit is treated in two independent meansA)DC analysis (B)AC analysis
3 @% T- O5 @- Y3 SThe separation between DC analysis and AC analysis greatly simplified a complex circuit.5 i+ k* S' T5 ]) A6 E4 ?3 Q
DC analysis is being carried out before AC analysis.
$ m. Z' Z2 ] dDC analysis determines the Q-point, including each node voltage and branch current.
; E. H' z9 i0 |AC analysis gives the frequency response, including bandwidth and gain.. V, |7 h0 z) i" D1 N; n7 x
Before performing AC Analysis, the DC operating point needed to be calculated from DC analysis first.
' l& v" j: n3 y# T: j, v a' jThis is to construct a linear small-signal model for the nonlinear component.* p; M# c: d4 Y; u# X3 }
So, the small signal (AC) response is highly dependent upon the presetting (DC) bias condition . h. f3 r! R2 B; J2 V
; s! |% d2 T1 {8 M; I9 uDC simulation in analog SPICE-like simulator, aims for computing the equilibrium points,
' @- e! j5 J/ \. E. Y* `which are the calculated DC node voltages and DC branch currents in a circuit.3 K& J# Y. }6 W: Q) d
They are the DC solutions of the DC equivalent equation/circuit.
! y! `/ d8 d; V6 `5 U+ V6 D0 AA circuit will only reach its equilibrium if its stimulus is off; v7 Q1 O+ A0 k4 i+ U1 d- {! \
and the independent sources are remain constantly employed. D8 L! x! G. d+ p/ M
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There is an important reason why a given electronics circuit always5 n+ o* u" d6 J# H1 z6 M
need to be reduced into a DC equivalent circuit (large-signal model)" E* \0 i. ?/ x$ G6 F6 r
and followed by an AC equivalent one(small-signal model).) d$ I' x" u O& w" u1 E) f
It has to do with the present of an active component in the circuit.! e8 e9 U1 J. z4 W* r# W
The active component is a nonlinear element.So, it will have to be linearized.
$ p7 N/ ~0 J7 _4 e$ ]' u8 }( ^The employment of active elements, like transistors, make the circuit a nonlinear algebra system.
5 J5 U4 ~) J3 ?' W" qNormally, the nonlinear equation can only be solved by means of iterative methods,
) j: Y4 t& S& [2 h+ nsuch as Newton-Raphson algorithm \cite{nlz!}. This algorithm transforms the solutions
9 Z7 h6 }- y2 l- M5 @$ u$ D/ Iof the nonlinear equation into a sequence of linear equation.
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