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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: w+ M! d; u% c1 d$ z, e$ v
4 {8 I! G; S: e- o* }This section highlights the importance of an accurate pre-determined DC compact model.\cite{dc!!!}
! C8 ?/ ^0 H! I7 {/ o& XFor compact model developers, extraction of the DC parameters always needs to be carried out before the extraction of AC ones.
( D, Z" X& p- g" Q1 x) gFor devices measurement, DC measurement has to be carried out before AC measurement. x$ s3 [5 H3 W, u9 g
For modern IC designers, DC analysis needs to be carried out before AC analysis.\cite[4.6.4]{smith!}; U I. {- D, n3 z# `
For SPICE-like simulators, DC simulation also needs to be swept first and then follows by AC simulation.\cite{nlz!}
- }2 Q8 e- T0 ~$ K* NFrom the device-level perspectives,9 Z! U3 Q; N% Q0 A0 I
a set of equations which describe the terminal characteristics of DUT are written in a compact model.
1 R7 j- }2 K) X9 j" }3 o# xThe equations are solved by SPICE-like simulators. ]. o2 v0 W! ~4 a8 X
The procedure of establishing equations, describing device's electrical characteristics, in a compact model0 y/ f' o" \0 P2 o. M
and have them solved by SPICE-like simulators is termed as: Device Characterization.7 y4 F! H) {2 Z1 N, {1 i) K% v! N1 x
The fully Characterizations are treated by two independent steps:
8 P0 O! i. T* ?: K0 a7 b(1)DC Characterization or DC parameters extraction; W8 j) d. T, q
(2)AC Characterization or AC parameters extraction& N& o" B! Z6 o
Characterizing a nonlinear electronics component always begins with
9 `) R+ Q, A" G5 P1 cDC characterization and follows by the AC characterization.
- F% K, |+ [- n" L e$ \Because the AC model is origined from the linearization of the DC model at an indicated operating point.
/ s7 D. z" U( \Accordingly, accuracy is highly required in DC characterization because of its piority in the procedure of parameter extraction .4 S" J) j& R" K* b- |, s/ v% `8 t0 `! @
; d+ \, w9 p( }& N. {8 ZFrom the circuit-level perspectives,,
! n9 d j$ m: u/ d+ k4 {) yCircuit analysis refers to solving a circuit with KVL and KCL.
. j$ \, R4 C6 ]( S2 b* I: S$ sTo be more specific, it means solving out nodes voltages and branches currents of each element in a circuit. l* f8 F) x. `- n. h
As the source of stimulus can be systematically separated into DC sources and AC sources,
9 P8 Z* G p5 T) u/ Zthe unknown/solutions of the circuit are also separated into DC part and AC part. ^% x* l9 J6 w
Analyzing a circuit is treated in two independent meansA)DC analysis (B)AC analysis
2 {6 o6 A1 V% hThe separation between DC analysis and AC analysis greatly simplified a complex circuit.. w% i0 W) G' C
DC analysis is being carried out before AC analysis.
' N( X+ R! Y9 c2 A9 ]. X( ^" ?DC analysis determines the Q-point, including each node voltage and branch current.
5 N* j$ O* ?0 ~- R4 BAC analysis gives the frequency response, including bandwidth and gain.# T4 D \5 m( j: ]- l
Before performing AC Analysis, the DC operating point needed to be calculated from DC analysis first.
9 _8 U' h/ L9 a! [This is to construct a linear small-signal model for the nonlinear component.0 b: a4 }; _$ [4 l3 h/ I
So, the small signal (AC) response is highly dependent upon the presetting (DC) bias condition .. j- o8 w+ G$ N' s |2 C, o9 r
! b, D, Z) D% u0 o DDC simulation in analog SPICE-like simulator, aims for computing the equilibrium points, |/ c1 y2 }( h; N2 ^6 k6 {0 V. U( M
which are the calculated DC node voltages and DC branch currents in a circuit.
8 n) [, n0 r! @5 w$ H9 eThey are the DC solutions of the DC equivalent equation/circuit.
: T! ?1 ]$ F/ u' N: ]; B" Q8 Z/ ^A circuit will only reach its equilibrium if its stimulus is off$ ^' Y. S+ [! r6 {6 E# N$ y0 i9 o
and the independent sources are remain constantly employed.# i. v- Y4 [/ k- j8 h4 f
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There is an important reason why a given electronics circuit always
/ b5 q1 v( j; jneed to be reduced into a DC equivalent circuit (large-signal model)4 j) C% t- s/ }# L+ Y" _
and followed by an AC equivalent one(small-signal model).
% V6 w! S' h2 _0 L! Q' {It has to do with the present of an active component in the circuit.
' p2 ^. X" E2 x9 x( M9 l/ D0 nThe active component is a nonlinear element.So, it will have to be linearized.
3 X6 N, p1 d) G( H$ nThe employment of active elements, like transistors, make the circuit a nonlinear algebra system.
% N" A/ O5 G4 t9 r& N4 yNormally, the nonlinear equation can only be solved by means of iterative methods,
0 t a7 |* f% S4 q6 t3 a% ^; y+ Bsuch as Newton-Raphson algorithm \cite{nlz!}. This algorithm transforms the solutions
% Q3 o. c2 P/ }1 H: B- Lof the nonlinear equation into a sequence of linear equation.8 j8 T% m3 t" @( p& Z
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