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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:0 n9 N) ]$ U9 O6 o
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This section highlights the importance of an accurate pre-determined DC compact model.\cite{dc!!!}( L U2 ~( b: l
For compact model developers, extraction of the DC parameters always needs to be carried out before the extraction of AC ones.
: M, ~# X( \7 v& I/ L) `- YFor devices measurement, DC measurement has to be carried out before AC measurement.
$ K* u% q3 i, i0 j0 ~' |: uFor modern IC designers, DC analysis needs to be carried out before AC analysis.\cite[4.6.4]{smith!}
; e$ J* N3 r4 LFor SPICE-like simulators, DC simulation also needs to be swept first and then follows by AC simulation.\cite{nlz!}
. s, p3 h+ g; P: Z( s% i. g1 x, xFrom the device-level perspectives,
$ s8 ^' H2 U& w% e- La set of equations which describe the terminal characteristics of DUT are written in a compact model.. d+ }& y. \- I7 A j8 U
The equations are solved by SPICE-like simulators.; k2 e4 B. h3 w; J5 `
The procedure of establishing equations, describing device's electrical characteristics, in a compact model
' l5 J; H# G+ u' {1 cand have them solved by SPICE-like simulators is termed as: Device Characterization.5 m! o8 x' c; c" U
The fully Characterizations are treated by two independent steps:
& P# ~( r" n5 q* |(1)DC Characterization or DC parameters extraction
) ]/ x# Z8 E+ b; s3 }3 i(2)AC Characterization or AC parameters extraction
! O4 D1 C& B" t9 y1 ^- z4 sCharacterizing a nonlinear electronics component always begins with" {. N+ B3 x4 b9 p
DC characterization and follows by the AC characterization.
2 ?: ~2 F1 v/ s6 FBecause the AC model is origined from the linearization of the DC model at an indicated operating point.8 { B0 d9 I' |0 Q7 s
Accordingly, accuracy is highly required in DC characterization because of its piority in the procedure of parameter extraction ., l3 B) J. [! Y, F4 c; s4 Q
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From the circuit-level perspectives,,- O, ]# s7 ]. i$ M0 T! |8 T
Circuit analysis refers to solving a circuit with KVL and KCL.
& h u% j( R1 D& N, gTo be more specific, it means solving out nodes voltages and branches currents of each element in a circuit.
( @+ }6 I/ n4 o. C0 Z$ ~As the source of stimulus can be systematically separated into DC sources and AC sources,( T: M/ G* [1 d5 z' v9 ` ]! l5 b
the unknown/solutions of the circuit are also separated into DC part and AC part.
8 @* }) i1 i5 D# wAnalyzing a circuit is treated in two independent meansA)DC analysis (B)AC analysis
, f R( q$ x3 qThe separation between DC analysis and AC analysis greatly simplified a complex circuit.: |+ N( Z% [' A3 i% c
DC analysis is being carried out before AC analysis.
" _1 d. i' f5 U% G9 a# i9 gDC analysis determines the Q-point, including each node voltage and branch current.
6 @$ n6 X, W5 P- o r# M" E% ~7 bAC analysis gives the frequency response, including bandwidth and gain.4 u; K4 [& _" [& p7 ~8 L
Before performing AC Analysis, the DC operating point needed to be calculated from DC analysis first." h. j0 [, ~: X+ h3 C" n
This is to construct a linear small-signal model for the nonlinear component.& F* K* M3 J% [( o" y3 K/ y
So, the small signal (AC) response is highly dependent upon the presetting (DC) bias condition .$ o) y5 k7 E' T: w- m0 o
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DC simulation in analog SPICE-like simulator, aims for computing the equilibrium points,
0 Y" p8 Y% x& T7 c( bwhich are the calculated DC node voltages and DC branch currents in a circuit.6 t+ m( \: l+ r6 ]: J, \
They are the DC solutions of the DC equivalent equation/circuit.: b# F @) a5 c
A circuit will only reach its equilibrium if its stimulus is off4 U \ x, p% j" [
and the independent sources are remain constantly employed.
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, w7 F* j9 u) p1 n6 ^! ]6 q; G2 fThere is an important reason why a given electronics circuit always1 a8 z9 _- ?9 x& E: o) j
need to be reduced into a DC equivalent circuit (large-signal model)! N a8 {5 `2 V! W. m5 |( b
and followed by an AC equivalent one(small-signal model).
" P* i! x7 {& r0 ^8 C0 W2 uIt has to do with the present of an active component in the circuit.& N g. l5 `7 e# ?) I3 P
The active component is a nonlinear element.So, it will have to be linearized.
[$ x, Q9 t' S" g; r+ u+ I' MThe employment of active elements, like transistors, make the circuit a nonlinear algebra system.: i6 r7 l+ E+ d( H
Normally, the nonlinear equation can only be solved by means of iterative methods,1 Y* v+ \7 Z j- R5 _0 Y# F1 V
such as Newton-Raphson algorithm \cite{nlz!}. This algorithm transforms the solutions
2 ]- F. i& s% a# yof the nonlinear equation into a sequence of linear equation.4 G9 ]/ g( {" }4 A1 f2 ?. A
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