Yüksek doğruluklu bir mosfet modelinin spice simülasyon programına dahil edilmesi
Başlık çevirisi mevcut değil.
- Tez No: 75338
- Danışmanlar: PROF. DR. HAKAN KUNTMAN
- Tez Türü: Yüksek Lisans
- Konular: Elektrik ve Elektronik Mühendisliği, Electrical and Electronics Engineering
- Anahtar Kelimeler: Benzetim, Mosfet modeli, Simulation, Mosfet model
- Yıl: 1998
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Devreler ve Sistemler Ana Bilim Dalı
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: Belirtilmemiş.
Özet
ÖZET Bu çalışmada, Ali Zeki ve Hakan Kuntman tarafından gerçekleştirilen analog tümdevre analizine uygun, yüksek doğruluklu bir MOSFET modelinin SPICE simülasyon programına dahil edilmesi konusu ele alınmıştır. Bu amaçla, SPICE3F4 olarak bilinen SPICE versiyonunun C dilinde yazılmış kodunda birtakım yeni düzenlemeler yapılmış ve modelin, mevcut SPICE MOSFET modellerine bir alternatif olarak devre simülasyonlarmda kullanılabilmesi sağlanmıştır. Modelin modifiye etmediği eleman davranışlarını modellemede mevcut MOSFET modellerinin analog tümdevre analizi için en etkini olduğu kabul edilen MOSFET LEVEL-3 modelinin eşitlikleri kullanılmıştır. vı
Özet (Çeviri)
SUMMARY IMPLEMENTATION OF AN ACCURATE MOSFET MODEL INTO SPICE SIMULATION PROGRAM 1 INTRODUCTION Computer simulation is one of the most important steps in electronic circuit design. Especially when IC design is concerned, simulation enables the circuit designer to perform a variety of analyses which otherwise would not be possible. Since simulation results are just as accurate as the device models used, modeling of semiconductor devices has been a very important field of interest among those concerning with IC design. On the other hand, MOSFETs have been the milestones of the present VLSI technology. Circuit designers need analogue MOS functional blocks for use in complete systems where digital and analogue subcircuits are manufactured on the same chip. Simultaneously with the increasing demand for accurate MOSFET models, the device dimensions have been decreasing due to the technological developments in VLSI fabrication process. Several MOSFET models have been developed to maintain the adequate accuracy for changing conditions in the technology. Among those, the model developed by Zeki and Kuntman seems to be one of the most suitable ones for computer simulation purposes since equations of this model have a low degree of complexity which in turn shortens the necessary CPU time for the simulation. Moreover, the model is able to represent the nonlinear electrical behavior of the device much more accurate than the present basic SPICE MOSFET models. Most of its parameters are of physical significance and only a few fit-in parameters are used. vnIn this thesis, implementation of the MOSFET model developed by Zeki and Kuntman into SPICE simulation program was carried out. For this purpose, the SPICE3F4 version was used. First, original model equations were introduced and then, necessary modifications due to numerical analysis techniques have been discussed. For modeling the MOSFET behaviors not given in that model, SPICE MOSFET level-3 equations were used. The accuracy of the model was demonstrated by comparing the simulation results with experimental data and SPICE level-3 MOSFET model simulation results. The new model is intended to be an alternative to the SPICE MOSFET models and their derivatives. 2 MODEL EQUATIONS The model equations which were obtained by combining the equations of Zeki-Kuntman model and SPICE level-3 MOSFET model are given in the following: Surface Inversion Potential: In the new model surface inversion potential was modified with a positive AV voltage. (f)B = 2<j>F + AV (1) AV = 6kT/q (2) Short Channel Effects: The equations used to represent the behavior of the short channel MOSFETs are given in the following: *i = 1-^- 'eff Xj,+WC i- wr \Xj+WpJ, Xj ?*? 0 ve wp ?*? 0 ise, aksi halde (3) vmwp=xd4*b-Vbs (4) 2er */>=. \qN, (5) sub ^- = 0.0831353 + 0.801 13929-^- - 0.01 1 1077 \XJ J (6) The above equations are the ones that are also used by SPICE level-3 MOSFET model. Since short channel effects were not represented by Zeki-Kuntman Model, the existing level-3 model equations were used in the new model. Body effect: In the new model, the equation used to represent the body effect in a MOS transistor's behavior is as follows: FB = M^B~VBS yFs 4J*b-V*s 1- 1 *Mb-vbs) ?+F., k2¥=0 ise, k2 = 0 ise (7) Here, k2 is a new fit-in parameter. Static feedback effect: Static feedback effect was represented using the following equation: Ku=Vfb+^b-o-Vds (8) Threshold voltage: In the new model threshold voltage was calculated using the following equation: IX' Th ~ ^bbc + Qb Cox (9) =vn +0b -ov“ +jFgTİh-rBS+FmyB -vBS) The connection between the weak and strong operation regions: Calculation of the voltage that is assumed to determine the border between the weak and the strong operation regions was carried out using the following equation: V”= r Th » kT Vn+ - I, '2“ ' tS, ' * \. B DO /IK»/» TO' If _£. f» V-^/ Cut-off region: The new model assumes a zero drain current in the cut-off region of operation. The dependance of mobility to terminal voltages: The mobility degradation due to the gate and bulk voltages were represented using the following equation. M”ı+eK-vn+2y(<ı>B-vBsyi2\ (11) Saturation Voltage The drain-source saturation voltage was calculated using the following equation: y~ = *wL“. (Vos -VT) = knQ- (VGS - VT) (12) Here, km is given byJç = _£ (13) 1 + - EC(L^-AL) where kv is a VDS independent coefficient which enables the continuity of the Sds ~ VDS curve at the nonsaturated and saturated operation regions' boundary. Velocity saturation: The factor used to modify the drain current expression when the velocity of the mobile carriers reachs to its saturation value is given by FD=- i+<r M > vSfl,*0 (14) Vsal^'eff DS where Ç is a new fit-in parameter. Channel Length Modulation: The new model uses the following equations to represent the channel length modulation if the values of xl and v^ parameters are different from zero. AL =- In A -|l/2 1 + A V DS 'Dsat ) IE. ~\”dS Vüsat* (15) A = ?\*oxXl (16) £c=- *e# (17) XIHere, x, is a fit-in parameter. If at least one of these parameters is zero the level-3 equation, i.e., AL = ^Kx2D(VDS-VDsal) ? (18) is used to represent the channel length modulation. Weak Inversion current: Subthreshold current expression is given in the following: I -I e kTx“ fl^ 1 D.weak x D.strong K \ x * 1 Here, IDstrong symbolize the value of the current that was calculated for VGS = Vm using the strong inversion current expressions. Saturation region current: The equation used to calculate the drain current in the saturation region is given by, Id -\K -Vn)2^'1* +*o), VDS >VDsat (20) where, w 0eff=T-MeffC'ox (21) and 2 -(l + fl^p Q'Dsat Bo - ^wo rv ~ ”.wo. @2) 1 + Eckir Xll3 ACCURACY LEVEL OF THE MODEL The current-voltage and conductance-voltage characteristics of an nMOS and a pMOS were simulated using the new model and the level-3 model. The results are given in figure- 1 and figure-2, respectively. 58.8 45.0 4a. a 25. a ıs. e 2.8 3-B“ ~~ 4'8 6.8 3.8 4.8 Figure 1 Current-voltage and conductance voltage characteristics for an nMOS transistor. xui-1 1,0*4 2. e 3. e 4. e 3. e 4. e -r”<n Figure 2 Current-voltage and conductance voltage characteristics for a pMOS transistor. It has been noted that the above characteristics are in accordance with the experimental data which were obtained by Zeki and Kuntman [2]. Several simulations were carried out in order to test the performance of the new model in comparison to the existing SPICE level-3 MOSFET model: A CMOS amplifier output stage, a simple OTA, a symmetrical OTA, a CCII+ and a wide range Gilbert multiplication circuit were simulated using both the level-3 model and the xivnew model. The results were seemed to appreciate the new model; it was able to give not only more accurate results than the level-3model was able to, but, it could generate those results as quick as the level-3 model, as well. 4 CONCLUSION In this study, an accurate MOSFET model was implemented into SPICE simulation program. The model equations were originally based on the Zeki- Kuntman model [2]. To simulate the effects that were not modified by Zeki-Kuntman model, level-3 SPICE MOSFET model equations were used. It has been demonstrated that the accuracy level of the new MOSFET model is better than that of the SPICE level-3 MOSFET model. Moreover, it has been noted that the CPU time required for the simulations of various analogue circuits using the new model is not more than the CPU time required for the level-3 simulations. The new model is intended to be an alternative to the basic SPICE MOSFET models and their derivatives. xv
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