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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:
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This section highlights the importance of an accurate pre-determined DC compact model.\cite{dc!!!}
9 a( `% V+ ]9 G3 S u+ QFor compact model developers, extraction of the DC parameters always needs to be carried out before the extraction of AC ones.1 P2 c5 x3 _, Y7 o
For devices measurement, DC measurement has to be carried out before AC measurement. D' `( Y& V1 J% m' U9 p: z
For modern IC designers, DC analysis needs to be carried out before AC analysis.\cite[4.6.4]{smith!}
9 ?. y; ?4 p' I6 X0 ~: o7 Y' wFor SPICE-like simulators, DC simulation also needs to be swept first and then follows by AC simulation.\cite{nlz!}
T5 {8 W6 _: Z; OFrom the device-level perspectives,0 c1 Y% y/ t+ ~$ n o$ g1 |0 J
a set of equations which describe the terminal characteristics of DUT are written in a compact model.
! E- Q7 x" q3 ]The equations are solved by SPICE-like simulators.# l$ A; t- ? m: y* f$ P
The procedure of establishing equations, describing device's electrical characteristics, in a compact model' q* T- k1 T0 d- h- y! |. J/ S; f
and have them solved by SPICE-like simulators is termed as: Device Characterization.
- Y' @$ [7 ]" T/ f8 o. E. f7 RThe fully Characterizations are treated by two independent steps:
8 I; E3 k; g( k, P% v# p/ `(1)DC Characterization or DC parameters extraction
% L# P$ @) ~( v! k" _(2)AC Characterization or AC parameters extraction |+ L& H' z- M# W
Characterizing a nonlinear electronics component always begins with
0 K! h/ P$ x' ^+ o+ \: Z4 v UDC characterization and follows by the AC characterization.
6 r5 Z% G0 C4 u+ u; X& fBecause the AC model is origined from the linearization of the DC model at an indicated operating point.+ ~. ]2 e4 W) E2 I3 P
Accordingly, accuracy is highly required in DC characterization because of its piority in the procedure of parameter extraction .
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From the circuit-level perspectives,,
a- |" H) |* J) ?% ^5 sCircuit analysis refers to solving a circuit with KVL and KCL.3 i a' `% q ^& ?4 `; C
To be more specific, it means solving out nodes voltages and branches currents of each element in a circuit.
" z, g% j# I Q) \. W+ ^As the source of stimulus can be systematically separated into DC sources and AC sources,
# e3 a# V4 ~4 X h+ Z; R) Rthe unknown/solutions of the circuit are also separated into DC part and AC part.9 d) @2 a, Y5 S
Analyzing a circuit is treated in two independent meansA)DC analysis (B)AC analysis2 r+ o+ _( A4 u
The separation between DC analysis and AC analysis greatly simplified a complex circuit.2 x9 a B* n/ ^6 h; ]
DC analysis is being carried out before AC analysis.
, q1 U# l9 S' H0 X7 R! r# _DC analysis determines the Q-point, including each node voltage and branch current.2 _* p' C% p% |( l9 V
AC analysis gives the frequency response, including bandwidth and gain.
+ x; j6 {( N' x b, S E3 pBefore performing AC Analysis, the DC operating point needed to be calculated from DC analysis first.
0 L3 e0 r4 n9 l) A% qThis is to construct a linear small-signal model for the nonlinear component.
% k4 x# S) [* \$ R" `0 X( wSo, the small signal (AC) response is highly dependent upon the presetting (DC) bias condition .$ b6 _7 S9 D; H. X
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DC simulation in analog SPICE-like simulator, aims for computing the equilibrium points,
/ l# l( g4 y- ^which are the calculated DC node voltages and DC branch currents in a circuit.) H+ ~. a/ t" i- F/ _
They are the DC solutions of the DC equivalent equation/circuit.
* h- M1 S9 J. k; F% t) S, p6 n( b5 I% {A circuit will only reach its equilibrium if its stimulus is off5 L0 k! ?, ?# ~* X: {
and the independent sources are remain constantly employed.
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5 d- n) p1 b$ {# g2 \: x6 tThere is an important reason why a given electronics circuit always9 t2 m5 t* |* S _, H
need to be reduced into a DC equivalent circuit (large-signal model)! v5 d) k2 _! I* x
and followed by an AC equivalent one(small-signal model).7 c5 c6 q/ \2 t# V" F9 y
It has to do with the present of an active component in the circuit.
* F9 |$ l& T: n! A! m: N$ RThe active component is a nonlinear element.So, it will have to be linearized.
( T1 M+ L" p. a5 V6 T' WThe employment of active elements, like transistors, make the circuit a nonlinear algebra system.- @$ w, m1 J$ Z7 k! q6 S
Normally, the nonlinear equation can only be solved by means of iterative methods,
# f* ^ ~* D- n7 zsuch as Newton-Raphson algorithm \cite{nlz!}. This algorithm transforms the solutions" o7 g7 U7 ]' B1 {) C. j- r8 ^, o
of the nonlinear equation into a sequence of linear equation.. M/ t4 r8 Z% e# m4 Q N* |3 M9 ]# o
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