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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!!!}6 l3 Z, R' Z5 c' ~
For compact model developers, extraction of the DC parameters always needs to be carried out before the extraction of AC ones.( A/ b+ s1 C3 l- H$ v
For devices measurement, DC measurement has to be carried out before AC measurement.
) E- e7 P- [& O, F5 m3 PFor modern IC designers, DC analysis needs to be carried out before AC analysis.\cite[4.6.4]{smith!}
3 _/ D* I$ Q. M& @For SPICE-like simulators, DC simulation also needs to be swept first and then follows by AC simulation.\cite{nlz!}" C* b+ V9 s+ \# {8 k2 m2 o$ d
From the device-level perspectives,
8 n7 T6 [, A/ @9 i7 \: v/ za set of equations which describe the terminal characteristics of DUT are written in a compact model.0 z2 h" B m4 S4 O
The equations are solved by SPICE-like simulators.
6 S$ g# y6 P( z6 e' D9 m7 \The procedure of establishing equations, describing device's electrical characteristics, in a compact model
6 D* V) j# z! E1 G0 t/ q* F* iand have them solved by SPICE-like simulators is termed as: Device Characterization.
$ K! a! P. {/ x5 _+ d p3 nThe fully Characterizations are treated by two independent steps:
: Z( ^. b. p- x( Z9 E(1)DC Characterization or DC parameters extraction- Y2 ?0 t: }9 n$ ?" d" k) X& A
(2)AC Characterization or AC parameters extraction
% j1 ?/ `% y# x! T' xCharacterizing a nonlinear electronics component always begins with7 a( J' G) f0 U
DC characterization and follows by the AC characterization.8 d) T1 j s- W; u' t+ \* K% {
Because the AC model is origined from the linearization of the DC model at an indicated operating point.
1 y- o2 e0 D! k" p9 IAccordingly, accuracy is highly required in DC characterization because of its piority in the procedure of parameter extraction .2 I$ B' {) R( n- B
5 k$ I& C I: n y" FFrom the circuit-level perspectives,,
$ T4 [' Z2 g7 E. i9 F6 u8 ~Circuit analysis refers to solving a circuit with KVL and KCL.
: L1 q+ L" K1 K3 u) ^' STo be more specific, it means solving out nodes voltages and branches currents of each element in a circuit.
7 r: S) z: {, l; i _5 KAs the source of stimulus can be systematically separated into DC sources and AC sources,
! J, h% b# ]+ ?; f$ K5 bthe unknown/solutions of the circuit are also separated into DC part and AC part.3 t2 D7 o2 |; |1 W+ [
Analyzing a circuit is treated in two independent meansA)DC analysis (B)AC analysis/ \0 X/ d1 ~9 Y2 Z& T0 d" O9 ?/ p6 ^
The separation between DC analysis and AC analysis greatly simplified a complex circuit.
5 P0 h# D! O! L7 m& YDC analysis is being carried out before AC analysis.' e2 s) ?/ e. m2 E9 r! l P: N2 x
DC analysis determines the Q-point, including each node voltage and branch current.7 |/ z' O8 h& W. `% T3 J9 j7 P
AC analysis gives the frequency response, including bandwidth and gain.
8 n- L' C4 w Y2 \) nBefore performing AC Analysis, the DC operating point needed to be calculated from DC analysis first.
9 p. u1 r& v8 z% O1 w8 YThis is to construct a linear small-signal model for the nonlinear component.
8 g8 G, h6 g8 d: S' P0 T7 w( Y2 HSo, the small signal (AC) response is highly dependent upon the presetting (DC) bias condition ., F: P6 R; W+ B, z# G
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DC simulation in analog SPICE-like simulator, aims for computing the equilibrium points,
% Y2 n0 T9 d) L! L4 uwhich are the calculated DC node voltages and DC branch currents in a circuit.4 ~$ Y: r; s {
They are the DC solutions of the DC equivalent equation/circuit.1 s, h% U( j! ~7 x# |# v
A circuit will only reach its equilibrium if its stimulus is off' P9 N3 @: ~* y+ @* d2 ]/ O
and the independent sources are remain constantly employed.
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There is an important reason why a given electronics circuit always
* [) [( I! @) T2 Vneed to be reduced into a DC equivalent circuit (large-signal model)9 S4 x# `% h, r5 I ~$ D! H
and followed by an AC equivalent one(small-signal model).
! \. r$ |6 C0 m2 B1 L- rIt has to do with the present of an active component in the circuit.; z0 u- d- e! d+ A1 K+ \4 ~! B6 w0 g
The active component is a nonlinear element.So, it will have to be linearized.
+ j3 D3 ]+ f. W% \& O' @% ]* OThe employment of active elements, like transistors, make the circuit a nonlinear algebra system.
, z8 p& m. C1 `/ L' T; u- `Normally, the nonlinear equation can only be solved by means of iterative methods,0 q3 c+ \5 `6 G# l/ W7 H. a
such as Newton-Raphson algorithm \cite{nlz!}. This algorithm transforms the solutions8 K3 y' j- E3 f$ t7 ?+ u: y# j3 R
of the nonlinear equation into a sequence of linear equation.
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