summaryrefslogtreecommitdiffstatshomepage
path: root/src/lib/netlist/analog/nld_mosfet.cpp
blob: e8cbdf64bcbc6246a0cb3c91b8e3a955373281db (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
// license:GPL-2.0+
// copyright-holders:Couriersud

//
// nld_mosfet.cpp
//
// Formulas in here based on the following Sources:
//
// https://www.imperial.ac.uk/pls/portallive/docs/1/7292573.PDF
// http://www3.imperial.ac.uk/pls/portallive/docs/1/56133736.PDF
// https://people.rit.edu/lffeee/SPICE_MOSFET_Model_Intro.pdf
// https://people.rit.edu/lffeee/SPICE.pdf
// http://web.mit.edu/course/6/6.012/SPR98/www/lectures/S98_Lecture10.pdf
// http://homepages.rpi.edu/~sawyes/Models_review.pdf
// http://jaco.ec.t.kanazawa-u.ac.jp/edu/mix/pdf/3.pdf
//
// Farid N. Naim, Circuit Simulation (Wiley-IEEE Press, 2010).
// Stefan Jahn, Michael Margraf, Vincent Habchi and Raimund Jacob, "Qucs Technical Papers" (2007)
//

#include "netlist/solver/nld_solver.h"
#include "netlist/nl_setup.h"
#include "nlid_twoterm.h"

#define BODY_CONNECTED_TO_SOURCE    (1)

namespace netlist
{
namespace analog
{

	using constants = plib::constants<nl_fptype>;

	// -----------------------------------------------------------------------------
	// nld_FET - Base classes
	// -----------------------------------------------------------------------------

	/// \brief Class representing the nmos/pmos model paramers.
	///
	///  This is the model representation of the nmos model.
	///
	///  Netlist has an additional parameter caller CAPMOD:
	///
	///  CAPMOD=0: Capacitance model disabled
	///  CAPMOD=2: Meyer capacitance model
	///
	///  Typically, SPICE uses the following parameters. A "Y" in the first
	///  column indicates that the parameter is actually used in netlist.
	///
	/// | NL? |Name  |                                                            Description|Units  |Default   |Example          |
	/// |:---:|------|-----------------------------------------------------------------------|-------|---------:|----------------:|
	/// |  Y  |Vto   | Zero-bias threshold voltage                                           | V     | 0        | 1               |
	/// |  Y  |Kp    | Transconductance parameter                                            | A/V²  | 0.00002  | 0.00003         |
	/// |  Y  |Gamma | Bulk threshold parameter                                              | V^½   | 0        | 0.37            |
	/// |  Y  |Phi   | Surface inversion potential                                           | V     | 0.6      | 0.65            |
	/// |  Y  |Lambda| Channel-length modulation (level 1 and 2 only)                        | 1/V   | 0        | 0.02            |
	/// |     |Rd    | Drain ohmic resistance                                                |W|0|1|
	/// |     |Rs    | Source ohmic resistance                                               |W|0|1|
	/// |     |Cbd   | Zero-bias B-D junction capacitance                                    |F|0|20f|
	/// |     |Cbs   | Zero-bias B-S junction capacitance                                    |F|0|20f|
	/// |  Y  |Is    | Bulk junction saturation current                                      |A|0.00000000000001|1E-015|
	/// |  Y  |N     | Bulk diode emission coefficient                                       |-|1|*|
	/// |     |Pb    | Bulk junction potential                                               |V|0.8|0.87|
	/// |  Y  |Cgso  | Gate-source overlap capacitance per meter channel width               |F/m|0|0.00000000004|
	/// |  Y  |Cgdo  | Gate-drain overlap capacitance per meter channel width                |F/m|0|0.00000000004*|
	/// |  Y  |Cgbo  | Gate-bulk overlap capacitance per meter channel width                 |F/m|0|0.0000000002*|
	/// |     |Rsh   | Drain and source diffusion sheet resistance                           |W|0|10*|
	/// |     |Cj    | Zero-bias bulk junction bottom capacitance per square meter of junction area|F/m²|0|0.0002*|
	/// |     |Mj    | Bulk junction bottom grading coefficient                              |-|0.5|0.5*|
	/// |     |Cjsw  | Zero-bias bulk junction sidewall capacitance per meter of junction perimeter|F/m|0|1p*|
	/// |     |Mjsw  | Bulk junction sidewall grading coefficient                            |-|.50 level 1  .33 level 2,3||
	/// |     |Js    | Bulk junction saturation current per square-meter of junction area|A/m|0|0.00000001|
	/// |  Y  |Tox   | Oxide thickness                                                       |m|0.0000001|0.0000001|
	/// |  Y  |Nsub  | Substrate doping                                                      |1/cm³|0|4000000000000000|
	/// |     |Nss   | Surface state density                                                 |1/cm²|0|10000000000|
	/// |     |Nfs   | Fast surface state                                                    |1/cm²|0|10000000000*|
	/// |     |TPG   | Type of gate material:  +1 opp. to substrate -1 same as substrate     |Al gate|-|1|
	/// |     |Xj    | Metallurgical junction depth                                          |m|0|1µ*|
	/// |  Y  |Ld    | Lateral diffusion                                                     |m|0|0.8µ|
	/// |  Y  |Uo    | Surface mobility                                                      |cm²/V/s|600|700|
	/// |     |Ucrit | Critical field for mobility degradation (level 2 only)                |V/cm|10000|10000|
	/// |     |Uexp  | Critical field exponent in mobility degradation (level 2 only)        |-|0|0.1|
	/// |     |Utra  | Transverse field coefficient (level 2 only)                           |-|0|0.3*|
	/// |     |Vmax  | Maximum carrier drift velocity (levels 2 & 3 only)                    |m/s|0|50000|
	/// |     |Neff  | Total channel-charge exponent (level 2 only)                          |-|1|5|
	/// |     |Kf    | Flicker noise coefficient                                             |-|0|1E-026|
	/// |     |Af    | Flicker noise exponent                                                |-|1|1.2|
	/// |     |Fc    | Coefficient for forward-bias depletion capacitance formula            |-|0.5||
	/// |     |Delta | Width effect on threshold voltage(levels 2 and 3)                     |-|0|1|
	/// |     |Theta | Mobility modulation (level 3 only)                                    |-|0|0.1|
	/// |     |Eta   | Static feedback (level 3 only)                                        |-|0|1|
	/// |     |Kappa | Saturation field (level 3 only)                                       |-|0.2|0.5|
	/// |     |Tnom  | Parameter measurement temperature                                     |ºC|27|50|
	/// |  Y  |L     | Length scaling                                                        |-|100e-6||
	/// |  Y  |W     | Width scaling                                                         |-|100e-6||
	///

	class fet_model_t : public param_model_t
	{
	public:
		fet_model_t(device_t &device, const pstring &name, const pstring &val)
		: param_model_t(device, name, val)
		, m_VTO(*this,  "VTO")
		, m_N(*this,  "N")
		, m_ISS(*this,  "IS")  // Haven't seen a model using ISS / ISD
		, m_ISD(*this,  "IS")
		, m_LD(*this,  "LD")
		, m_L(*this, "L")
		, m_W(*this, "W")
		, m_TOX(*this, "TOX")
		, m_KP(*this, "KP")
		, m_UO(*this, "UO")
		, m_PHI(*this, "PHI")
		, m_NSUB(*this, "NSUB")
		, m_GAMMA(*this, "GAMMA")
		, m_LAMBDA(*this, "LAMBDA")
		, m_RD(*this, "RD")
		, m_RS(*this, "RS")
		, m_CGSO(*this, "CGSO")
		, m_CGDO(*this, "CGDO")
		, m_CGBO(*this, "CGBO")
		, m_CAPMOD(*this, "CAPMOD")
		{}

		value_t m_VTO;      //!< Threshold voltage [V]
		value_t m_N;        //!< Bulk diode emission coefficient
		value_t m_ISS;      //!< Body diode saturation current
		value_t m_ISD;      //!< Body diode saturation current
		value_t m_LD;       //!< Lateral diffusion [m]
		value_t m_L;        //!< Length scaling
		value_t m_W;        //!< Width scaling
		value_t m_TOX;      //!< Oxide thickness
		value_t m_KP;       //!< Transconductance parameter [A/V²]
		value_t m_UO;       //!< Surface mobility [cm²/V/s]
		value_t m_PHI;      //!< Surface inversion potential [V]
		value_t m_NSUB;     //!< Substrate doping [1/cm³]
		value_t m_GAMMA;    //!< Bulk threshold parameter [V^½]
		value_t m_LAMBDA;   //!< Channel-length modulation [1/V]
		value_t m_RD;       //!< Drain ohmic resistance
		value_t m_RS;       //!< Source ohmic resistance
		value_t m_CGSO;     //!< Gate-source overlap capacitance per meter channel width
		value_t m_CGDO;     //!< Gate-drain overlap capacitance per meter channel width
		value_t m_CGBO;     //!< Gate-bulk overlap capacitance per meter channel width
		value_base_t<int> m_CAPMOD; //!< Capacitance model (0=no model 2=Meyer)
	};

	// Have a common start for mosfets

	NETLIB_OBJECT(FET)
	{
	public:
		enum q_type {
			FET_NMOS,
			FET_PMOS
		};

		NETLIB_CONSTRUCTOR(FET)
		, m_model(*this, "MODEL", "NMOS")
		, m_qtype(FET_NMOS)
		{
		}

		NETLIB_IS_DYNAMIC(true)

		//NETLIB_RESETI();
		NETLIB_UPDATEI() { }

		q_type qtype() const noexcept { return m_qtype; }
		bool is_qtype(q_type atype) const noexcept { return m_qtype == atype; }
		void set_qtype(q_type atype) noexcept { m_qtype = atype; }
	protected:

		fet_model_t m_model;
	private:
		q_type m_qtype;
	};

	// -----------------------------------------------------------------------------
	// nld_QBJT_EB
	// -----------------------------------------------------------------------------

	NETLIB_OBJECT_DERIVED(MOSFET, FET)
	{
	public:
		NETLIB_CONSTRUCTOR_DERIVED(MOSFET, FET)
		, m_DG(*this, "m_DG", true)
		, m_SG(*this, "m_SG", true)
		, m_SD(*this, "m_SD", true)
		, m_D_BD(*this, "m_D_BD")
#if (!BODY_CONNECTED_TO_SOURCE)
		, m_D_BS(*this, "m_D_BS")
#endif
		, m_cap_gb(*this, "m_cap_gb")
		, m_cap_gs(*this, "m_cap_gs")
		, m_cap_gd(*this, "m_cap_gd")
		, m_phi(nlconst::zero())
		, m_gamma(nlconst::zero())
		, m_vto(nlconst::zero())
		, m_beta(nlconst::zero())
		, m_lambda(nlconst::zero())
		, m_Leff(nlconst::zero())
		, m_CoxWL(nlconst::zero())
		, m_polarity(nlconst::magic(qtype() == FET_NMOS ? 1.0 : -1.0))
		, m_Cgb(nlconst::zero())
		, m_Cgs(nlconst::zero())
		, m_Cgd(nlconst::zero())
		, m_capmod(2)
		, m_Vgs(*this, "m_Vgs", nlconst::zero())
		, m_Vgd(*this, "m_Vgd", nlconst::zero())
	{
			register_subalias("S", m_SG.m_P);   // Source
			register_subalias("G", m_SG.m_N);   // Gate

			register_subalias("D", m_DG.m_P);   // Drain

			connect(m_SG.m_P, m_SD.m_P);
			connect(m_SG.m_N, m_DG.m_N);
			connect(m_DG.m_P, m_SD.m_N);

			set_qtype((m_model.type() == "NMOS_DEFAULT") ? FET_NMOS : FET_PMOS);
			m_polarity = nlconst::magic((qtype() == FET_NMOS) ? 1.0 : -1.0);

			m_capmod = m_model.m_CAPMOD;
			// printf("capmod %d %g %g\n", m_capmod, (nl_fptype)m_model.m_VTO, m_polarity);
			nl_assert_always(m_capmod == 0 || m_capmod == 2, "Error: CAPMODEL invalid value");

			//
			// From http://ltwiki.org/LTspiceHelp/LTspiceHelp/M_MOSFET.htm :
			//
			//      VTO, KP, LAMBDA, PHI and GAMMA. These parameters are computed
			//      if the process parameters(NSUB, TOX,...) are given, but
			//      user-specified values always override.
			//
			//  But couldn't find a formula for lambda anywhere
			//

			m_lambda = m_model.m_LAMBDA; // FIXME: m_lambda only set once

			// calculate effective channel length
			m_Leff = m_model.m_L - 2 * m_model.m_LD;
			nl_assert_always(m_Leff > nlconst::zero(), "Effective Lateral diffusion would be negative for model");

			nl_fptype Cox = (m_model.m_TOX > nlconst::zero()) ? (constants::eps_SiO2() * constants::eps_0() / m_model.m_TOX) : nlconst::zero();

			// calculate DC transconductance coefficient
			if (m_model.m_KP > nlconst::zero())
				m_beta = m_model.m_KP * m_model.m_W / m_Leff;
			else if (Cox > nlconst::zero() && m_model.m_UO > nlconst::zero())
				m_beta = m_model.m_UO * nlconst::magic(1e-4) * Cox * m_model.m_W / m_Leff;
			else
				m_beta = nlconst::magic(2e-5) * m_model.m_W / m_Leff;

			//FIXME::UT can disappear
			const nl_fptype Vt = constants::T0() * constants::k_b() / constants::Q_e();

			// calculate surface potential if not given

			if (m_model.m_PHI > nlconst::zero())
				m_phi = m_model.m_PHI;
			else if (m_model.m_NSUB > nlconst::zero())
			{
				nl_assert_always(m_model.m_NSUB * nlconst::magic(1e6) >= constants::NiSi(), "Error calculating phi for model");
				m_phi = nlconst::two() * Vt * plib::log (m_model.m_NSUB * nlconst::magic(1e6) / constants::NiSi());
			}
			else
				m_phi = nlconst::magic(0.6);

			// calculate bulk threshold if not given
			if (m_model.m_GAMMA > nlconst::zero())
				m_gamma = m_model.m_GAMMA;
			else
			{
				if (Cox > nlconst::zero() && m_model.m_NSUB > nlconst::zero())
					m_gamma = plib::sqrt (nlconst::two()
						* constants::Q_e() * constants::eps_Si() * constants::eps_0()
						* m_model.m_NSUB * nlconst::magic(1e6)) / Cox;
				else
					m_gamma = nlconst::zero();
			}

			m_vto = m_model.m_VTO;
			// FIXME zero conversion
			if(m_vto != nlconst::zero())
				log().warning(MW_MOSFET_THRESHOLD_VOLTAGE(m_model.name()));

			// FIXME: VTO if missing may be calculated from TPG, NSS and temperature. Usually models
			// specify VTO so skip this here.

			m_CoxWL = Cox * m_model.m_W * m_Leff;

			//printf("Cox: %g\n", m_Cox);
		}

		NETLIB_IS_TIMESTEP(true || m_capmod != 0)

		NETLIB_TIMESTEPI()
		{
			if (m_capmod != 0)
			{
				//const nl_nl_fptype Ugd = -m_DG.deltaV() * m_polarity; // Gate - Drain
				//const nl_nl_fptype Ugs = -m_SG.deltaV() * m_polarity; // Gate - Source
				const nl_fptype Ugd = m_Vgd; // Gate - Drain
				const nl_fptype Ugs = m_Vgs; // Gate - Source
				const nl_fptype Ubs = nlconst::zero(); // Bulk - Source == 0 if connected
				const nl_fptype Ugb = Ugs - Ubs;

				m_cap_gb.timestep(m_Cgb, Ugb, step);
				m_cap_gs.timestep(m_Cgs, Ugs, step);
				m_cap_gd.timestep(m_Cgd, Ugd, step);
			}
		}

	protected:

		NETLIB_RESETI()
		{
			NETLIB_NAME(FET)::reset();
			// Bulk diodes

			m_D_BD.set_param(m_model.m_ISD, m_model.m_N, exec().gmin(), constants::T0());
			#if (!BODY_CONNECTED_TO_SOURCE)
				m_D_BS.set_param(m_model.m_ISS, m_model.m_N, exec().gmin(), constants::T0());
			#endif
		}

		NETLIB_UPDATEI();
		NETLIB_UPDATE_PARAMI();
		NETLIB_UPDATE_TERMINALSI();

	private:

		nld_twoterm m_DG;
		nld_twoterm m_SG;
		nld_twoterm m_SD;

		generic_diode<diode_e::MOS> m_D_BD;
#if (!BODY_CONNECTED_TO_SOURCE)
		generic_diode<diode_e::MOS> m_D_BS;
#endif

		generic_capacitor<capacitor_e::VARIABLE_CAPACITY> m_cap_gb;
		generic_capacitor<capacitor_e::VARIABLE_CAPACITY> m_cap_gs;
		generic_capacitor<capacitor_e::VARIABLE_CAPACITY> m_cap_gd;

		nl_fptype m_phi;
		nl_fptype m_gamma;
		nl_fptype m_vto;
		nl_fptype m_beta;
		nl_fptype m_lambda;

		// used in capacitance calculation
		nl_fptype m_Leff;
		nl_fptype m_CoxWL;
		nl_fptype m_polarity;

		// capacitance values

		nl_fptype m_Cgb;
		nl_fptype m_Cgs;
		nl_fptype m_Cgd;

		int m_capmod;
		state_var<nl_fptype> m_Vgs;
		state_var<nl_fptype> m_Vgd;

		void set_cap(generic_capacitor<capacitor_e::VARIABLE_CAPACITY> cap,
			nl_fptype capval, nl_fptype V,
			nl_fptype &g11, nl_fptype &g12, nl_fptype &g21, nl_fptype &g22,
			nl_fptype &I1, nl_fptype &I2) const
		{
			const nl_fptype I = cap.Ieq(capval, V) * m_polarity;
			const nl_fptype G = cap.G(capval);
			g11 += G; g12 -= G; g21 -= G; g22 += G;
			I1 -= I; I2 += I;
			//printf("Cap: %g\n", capval);
		}

		void calculate_caps(nl_fptype Vgs, nl_fptype Vgd, nl_fptype Vth,
			nl_fptype &Cgs, nl_fptype &Cgd, nl_fptype &Cgb) const
		{
			nl_fptype Vctrl = Vgs - Vth * m_polarity;
			// Cut off - now further differentiated into 3 different formulas
			// Accumulation
			if (Vctrl <= -m_phi)
			{
				Cgb = m_CoxWL;
				Cgs = nlconst::zero();
				Cgd = nlconst::zero();
			}
			else if (Vctrl <= -m_phi / nlconst::two())
			{
				Cgb = -Vctrl * m_CoxWL / m_phi;
				Cgs = nlconst::zero();
				Cgd = nlconst::zero();
			}
			// Depletion
			else if (Vctrl <= 0)
			{
				Cgb = -Vctrl * m_CoxWL / m_phi;
				Cgs = Vctrl * m_CoxWL * nlconst::magic(4.0 / 3.0) / m_phi + nlconst::magic(2.0 / 3.0) * m_CoxWL;
				Cgd = nlconst::zero();
			}
			else
			{
				const nl_fptype Vdsat = Vctrl;
				const nl_fptype Vds = Vgs - Vgd;
				// saturation
				if (Vdsat <= Vds)
				{
					Cgb = nlconst::zero();
					Cgs = nlconst::magic(2.0 / 3.0) * m_CoxWL;
					Cgd = nlconst::zero();
				}
				else
				{
					// linear
					const auto Sqr1(static_cast<nl_fptype>(plib::pow(Vdsat - Vds, 2)));
					const auto Sqr2(static_cast<nl_fptype>(plib::pow(nlconst::two() * Vdsat - Vds, 2)));
					Cgb = 0;
					Cgs = m_CoxWL * (nlconst::one() - Sqr1 / Sqr2) * nlconst::magic(2.0 / 3.0);
					Cgd = m_CoxWL * (nlconst::one() - Vdsat * Vdsat / Sqr2) * nlconst::magic(2.0 / 3.0);
				}
			}
		}
	};

	// ----------------------------------------------------------------------------------------
	// MOSFET
	// ----------------------------------------------------------------------------------------

	NETLIB_UPDATE(MOSFET)
	{
		// FIXME: This should never be called
		if (!m_SG.m_P.net().isRailNet())
			m_SG.m_P.solve_now();   // Basis
		else if (!m_SG.m_N.net().isRailNet())
			m_SG.m_N.solve_now();   // Emitter
		else
			m_DG.m_N.solve_now();   // Collector
	}

	NETLIB_UPDATE_TERMINALS(MOSFET)
	{
		nl_fptype Vgd = -m_DG.deltaV() * m_polarity; // Gate - Drain
		nl_fptype Vgs = -m_SG.deltaV() * m_polarity; // Gate - Source

		// limit step sizes

		const nl_fptype k = nlconst::magic(3.5); // see "Circuit Simulation", page 185
		nl_fptype d = (Vgs - m_Vgs);
		Vgs = m_Vgs + plib::reciprocal(k) * nlconst::magic(d < 0 ? -1.0 : 1.0) * plib::log1p(k * plib::abs(d));
		d = (Vgd - m_Vgd);
		Vgd = m_Vgd + plib::reciprocal(k) * nlconst::magic(d < 0 ? -1.0 : 1.0) * plib::log1p(k * plib::abs(d));

		m_Vgs = Vgs;
		m_Vgd = Vgd;

		const nl_fptype Vbs = nlconst::zero(); // Bulk - Source == 0 if connected
		//const nl_nl_fptype Vbd = m_SD.deltaV() * m_polarity;  // Bulk - Drain = Source  - Drain
		const nl_fptype Vds = Vgs - Vgd;
		const nl_fptype Vbd = -Vds;  // Bulk - Drain = Source  - Drain

#if (!BODY_CONNECTED_TO_SOURCE)
		m_D_BS.update_diode(Vbs);
#endif
		m_D_BD.update_diode(Vbd);

		// Are we in forward mode ?
		// in backward mode, just swap source and drain
		const bool is_forward = Vds >= nlconst::zero();

		// calculate Vth
		const nl_fptype Vbulk = is_forward ? Vbs : Vbd;
		const nl_fptype phi_m_Vbulk = (m_phi > Vbulk) ? plib::sqrt(m_phi - Vbulk) : nlconst::zero();
		const nl_fptype Vth = m_vto * m_polarity + m_gamma * (phi_m_Vbulk - plib::sqrt(m_phi));

		const nl_fptype Vctrl = (is_forward ? Vgs : Vgd) - Vth;

		nl_fptype Ids(0);
		nl_fptype gm(0);
		nl_fptype gds(0);
		nl_fptype gmb(0);

		const nl_fptype absVds = plib::abs(Vds);

		if (Vctrl <= nlconst::zero())
		{
			// cutoff region
			Ids = nlconst::zero();
			gm  = nlconst::zero();
			gds = nlconst::zero();
			gmb = nlconst::zero();
		}
		else
		{
			const nl_fptype beta = m_beta * (nlconst::one() + m_lambda * absVds);
			if (Vctrl <= absVds)
			{
				// saturation region
				Ids = beta * Vctrl * Vctrl / nlconst::two();
				gm  = beta * Vctrl;
				gds = m_lambda * m_beta * Vctrl * Vctrl / nlconst::two();
			}
			else
			{
				// linear region
				Ids = beta * absVds * (Vctrl - absVds / nlconst::two());
				gm  = beta * absVds;
				gds = beta * (Vctrl - absVds) + m_lambda * m_beta * absVds * (Vctrl - absVds / nlconst::two());
			}

			// backgate transconductance
			const nl_fptype bgtc = (phi_m_Vbulk != nlconst::zero()) ? (m_gamma / phi_m_Vbulk / nlconst::two()) : nlconst::zero();
			gmb = gm * bgtc;
		}

		// FIXME: these are needed to compute capacitance
		// nl_fptype Udsat = pol * std::max (Utst, 0.0);
		// Uon = pol * Vth;

		// compute bulk diode equivalent currents

		const nl_fptype IeqBD = m_D_BD.Ieq();
		const nl_fptype gbd = m_D_BD.G();

#if (!BODY_CONNECTED_TO_SOURCE)
		const nl_fptype IeqBS = m_D_BS.Ieq();
		const nl_fptype gbs = m_D_BS.G();
#else
		const nl_fptype IeqBS = nlconst::zero();
		const nl_fptype gbs = nlconst::zero();
#endif
		// exchange controlling nodes if necessary
		const nl_fptype gsource = is_forward ? (gm + gmb) : nlconst::zero();
		const nl_fptype gdrain  = is_forward ? nlconst::zero() : (gm + gmb);

		const nl_fptype IeqDS = (is_forward) ?
			   Ids - gm * Vgs - gmb * Vbs - gds * Vds
			: -Ids - gm * Vgd - gmb * Vbd - gds * Vds;

		// IG = 0
		nl_fptype IG = nlconst::zero();
		nl_fptype ID = (+IeqBD - IeqDS) * m_polarity;
		nl_fptype IS = (+IeqBS + IeqDS) * m_polarity;
		nl_fptype IB = (-IeqBD - IeqBS) * m_polarity;

		nl_fptype gGG = nlconst::zero();
		nl_fptype gGD = nlconst::zero();
		nl_fptype gGS = nlconst::zero();
		nl_fptype gGB = nlconst::zero();

		nl_fptype gDG =  gm;
		nl_fptype gDD =  gds + gbd - gdrain;
		const nl_fptype gDS = -gds - gsource;
		const nl_fptype gDB =  gmb - gbd;

		nl_fptype gSG = -gm;
		const nl_fptype gSD = -gds + gdrain;
		nl_fptype gSS =  gbs + gds + gsource;
		const nl_fptype gSB = -gbs - gmb;

		nl_fptype gBG =  nlconst::zero();
		const nl_fptype gBD = -gbd;
		const nl_fptype gBS = -gbs;
		nl_fptype gBB =  gbs + gbd;

		if (m_capmod != 0)
		{
			const nl_fptype Vgb = Vgs - Vbs;

			if (is_forward)
				calculate_caps(Vgs, Vgd, Vth, m_Cgs, m_Cgd, m_Cgb);
			else
				calculate_caps(Vgd, Vgs, Vth, m_Cgd, m_Cgs, m_Cgb);

			set_cap(m_cap_gb, m_Cgb + m_model.m_CGBO * m_Leff, Vgb, gGG, gGB, gBG, gBB, IG, IB);
			set_cap(m_cap_gs, m_Cgs + m_model.m_CGSO * m_model.m_W, Vgs, gGG, gGS, gSG, gSS, IG, IS);
			set_cap(m_cap_gd, m_Cgd + m_model.m_CGDO * m_model.m_W, Vgd, gGG, gGD, gDG, gDD, IG, ID);
		}

		// Source connected to body, Diode S-B shorted!
		const nl_fptype gSSBB = gSS + gBB + gBS + gSB;
		const auto zero(nlconst::zero());
		//                 S          G
		m_SG.set_mat(    gSSBB,   gSG + gBG, +(IS + IB),       // S
					   gGS + gGB,    gGG,      IG       );     // G
		//                 D          G
		m_DG.set_mat(     gDD,       gDG,    +ID,              // D
						  gGD,      zero,   zero        );     // G
		//                 S          D
		m_SD.set_mat(    zero,    gSD + gBD, zero,             // S
					   gDS + gDB,   zero,    zero);            // D
	}

	NETLIB_UPDATE_PARAM(MOSFET)
	{
	}

} // namespace analog

namespace devices {
	NETLIB_DEVICE_IMPL_NS(analog, MOSFET, "MOSFET", "MODEL")
} // namespace devices

} // namespace netlist