APPLICATION NOTE Varactor SPICE Models for RF VCO Applications The varactor SPICE model described in this application note is useful for RF voltage controlled oscillator (VCO) applications. However, the model neglects some parasitic components often needed for high frequency microwave applications, such as the distributed line package model and some capacitance due to ground proximity. A simplified equivalent circuit diagram for a varactor is shown in Figure 1. generates higher harmonics that affect performance of the VCO. In this case, a more detailed equivalent circuit model is needed. The technique used should be based on the varactor model extraction procedure from S-parameter data. A SPICE model and S-parameters, defined for the Libra IV environment, are shown in Figure 2. This model neglects the package capacitance, CP. The typical package capacitance value of 0.10 pF is absorbed within the junction capacitance, CJ. For most RF VCO applications to about 2.5 GHz, parasitic components would not be important unless the varactor CJ Junction Capacitance Cathode RS Series Resistance LS Anode Series Inductance D Junction Diode CP Parallel Capacitance Figure 1. Simplified Equivalent Varactor Circuit PORT P_anode port = 1 IND LS L = LS RES RS R = RS CAP CP C = CP DIODE Varactor_Diode AREA = 1 MODEL = Diode_Model MODE = nonlinear PORT P_Cathode port = 2 DIODEM Diode_Model IS = 1.00e-14 RS = 0 N=1 TT = 0 CJO = CJO M=M VJ = VJ EG = 1.11 XTI = 3 KF =0 AF =1 FC = 0.5 BV = VB IBV = 1e-3 ISR = 0 NR = 2 IKF = 0 NBV = 1 IBVL = 0 NBVL = 1 TBV1 = 0 TNOM = 27 FFE = 1 S1672 Figure 2. Libra IV SPICE Model Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 200315C • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • August 5, 2015 1 APPLICATION NOTE • VARACTOR SPICE MODELS Table 1. SPICE Model Parameters Parameter Unit Default Value Saturation current. With N, determines the DC characteristics of the diode. A 1e–14 RS Series resistance. Ω 0 N Emission coefficient. With IS, determines the DC characteristics of the diode. – 1 IS Description TT Transit time. sec 0 CJO Zero-bias junction capacitance. With VJ and M, defines nonlinear junction capacitance of the diode. F 0 VJ Junction potential. With CJO and M, defines nonlinear junction capacitance of the diode. V 1 M Grading coefficient. With CJO and VJ, defines nonlinear junction capacitance of the diode. – 0.5 EG Energy gap. With XTI, helps define the dependence of IS on temperature. EV 1.11 XTI Saturation current temperature exponent. With EG, helps define the dependence of IS on temperature. – 3 KF Flicker noise coefficient. – 0 AF Flicker noise exponent. – 1 FC Forward-bias depletion capacitance coefficient. – 0.5 Reverse breakdown voltage. V Infinity IBV Current at reverse breakdown voltage. A 1e–3 ISR Recombination current parameter. A 0 NR Emission coefficient for ISR parameter. – 2 BV/VB IKF High injection knee current. A Infinity NBV Reverse breakdown ideality factor. – 1 IBVL Low-level reverse breakdown knee current. A 0 NBVL Low-level reverse breakdown ideality factor. – 1 TNOM Nominal ambient temperature at which these model parameters were derived. °C 27 Flicker noise frequency exponent. – 1 FFE SPICE model parameters are defined in Table 1. Default values are noted that are appropriate for silicon varactor diodes, which may be used by the Libra IV simulator unless others are specifically defined. The effect of the diode junction is ignored in this model. This simplification ignores the rectifying effect of a diode during a positive voltage swing. However, for most RF VCO applications, the lowest practical DC control voltage value is 0.5 V and the magnitude of RF voltage rarely exceeds a peak of 0.2 V. Therefore, the varactor is maintained in its reverse bias state. However, with a large signal application where it is necessary to consider the rectifying properties of a diode, the effect of the diode can considered by entering additional diode parameters into the SPICE model defined for the Libra IV environment. The varactor junction capacitance, CJ, is a function of the applied reverse DC voltage, VR, as well as the parameters CJO, M, and VJ that are shown in Table 1. The SPICE model defines junction capacitance as a function of reverse voltage, VR, as follows: C J ( VR ) C JO V 1 R VJ M The total capacitance, CT, is the parallel combination of the junction capacitance and the package capacitance, CP: CT ( VR ) C JO V 1 R VJ M CP Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 2 (1) August 5, 2015 • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • 200315C (2) APPLICATION NOTE • VARACTOR SPICE MODELS The model is accurate for abrupt junction varactors (e.g., Skyworks SMV1400 Series). The model is less accurate for hyperabrupt junction varactors, but can be adapted to produce reasonably accurate simulation results. The form is similar to the traditional varactor equation but uses values for VJ, M, and CP that were extracted individually from measured CT(VR) data for each varactor part number. used should be taken from the specified maximum value or derived from its Q specification. Series inductance, LS, is also considered a constant value at 1.7 nH. This incorporates the 1.5 nH package inductance with some insertion inductance typical for PC boards in RF wireless applications. Table 2 provides values for the plastic packaged varactors that may be used with Equations 1 and 2. The series resistance, RS, is a function of the applied voltage and operating frequency, and may be considered constant. The value Table 2. SPICE Model Parameters for Skyworks Plastic Packaged Varactor Diodes (1 of 2) Part Number CJO (pF) VJ (V) M CP (pF) RS (Ω) SMV1129 27.5 2.8 1.1 0 0.4 SMV1145 41.8 2.5 2.2 0 0.6 SMV1206 26.11 4 1.45 0.3 0.7 SMV1212 72.47 110 67 4.5 0.45 SMV1213 28.9 190 105 2.2 0.8 SMV1214 22.74 190 106 1.5 0.7 SMV1215 14.36 190 115 1.1 1 SMV1232 4.2 1.7 0.9 0 1.5 SMV1233 4.12 1.7 0.9 0.7 1.2 SMV1234 8.75 2.3 1.1 1.2 0.8 SMV1235 16.13 8 4 2 0.6 SMV1236 21.63 8 4.2 3.2 0.5 SMV1237 66.16 10 5.3 9 0.13 SMV1245 6.9 3.5 1.7 0.47 2 SMV1247 9.22 100 100 0.55 2 SMV1248 21.54 13 10.5 0 1.8 SMV1249 39 17 14 0 1.5 SMV1251 60 17 14 0 1.3 SMV1253 70 17 14 0 1.2 SMV1255 82 17 14 0 1 SMV1405 2.92 0.68 0.41 0.05 0.8 SMV1408 3.7 0.8 0.43 0.13 0.6 SMV1413 9.2 0.79 0.45 0.13 0.35 SMV1493 29 0.63 0.47 0 0.25 SMV2205 12.427 4.077 1.455 0.075 1.21 SMV2204 7.162 4.196 1.439 0.075 2.19 SMV2203 4.716 3.72 1.31 0.075 2.76 SMV2202 3.159 3.944 1.305 0.075 3 SMV2201 2.097 2.984 1.199 0.075 5.41 SMV2026 8.8 1.05 0.65 0.07 0.8 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 200315C • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • August 5, 2015 3 APPLICATION NOTE • VARACTOR SPICE MODELS Table 2. SPICE Model Parameters for Skyworks Plastic Packaged Varactor Diodes (2 of 2) Part Number CJO (pF) VJ (V) M CP (pF) RS (Ω) SMV2025 8.8 1.05 0.7 0.07 0.8 SMV2019 2.25 3.5 1.4 0.07 4.8 SMV1801 85 10 4.4 2.6 1.1 SMV1771 41.6 12 8 2 0.45 SMV1770 33.07 43.4 30 3.54 0.4 SMV1763 7.63 26.7 20 1.42 0.5 SMV1705 31 3 2 0 0.32 SMV1702 92.65 25 12.76 0 0.5 SMV1470 110 80 39.7 3.94 0.5 SMV1281 13 14 6 0.62 1.7 SMV1276 6.75 0.18 0.41 0.18 0.8 SMV1275 4.7 0.18 0.41 0.18 0.8 SMV1273 31.7 0.18 0.5 0.18 0.8 SMV1272 29 0.38 0.6 0.07 0.5 SMV1270 30 12 8 2 0.7 SMV1265 22.5 30 13 0.71 2.4 SMV1263 8.2 15 9.5 0.67 1.2 SMV1231 1.88 10.13 4.999 0.44 2.5 SMV1220 48.43 13 9 3.2 0.52 SMV1130 25.8 10 3.7 1.8 0.8 SMV1430 1.11 0.86 0.5 0.13 3.15 The values shown in Table 2 can be used for each varactor junction in the SOD-323 and SOT-23 package types for these varactors. The Table also provides calculated values for the capacitance ratio between 0.5 and 2.5 V for each varactor. This is a typical voltage range for battery operated wireless VCO circuits. Note that the values listed in Table 2 for VJ, M, and CP were empirically determined and do not represent the precise physical or electronic properties of the semiconductor or the package type. Examples Figure 3 plots the calculated and measured SPICE model capacitance of the abrupt junction varactor SMV1493-011 against voltage. Figure 4 plots the calculated and measured SPICE model capacitance for the hyperabrupt junction varactor SMV1235-011 against voltage. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 4 August 5, 2015 • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • 200315C APPLICATION NOTE • VARACTOR SPICE MODELS 35 20 30 15 Capacitance (pF) Capacitance (pF) Approximation 25 20 15 10 5 SMV1235-011 10 SMV1493-011 Approximation 5 0 0 1 2 3 4 5 Varactor Voltage (V) Figure 3. SMV1493-011 Capacitance vs Voltage (CV = 29[1–VVAR/0.63]0.47) 6 0 2 4 6 8 10 12 Varactor Voltage (V) Figure 4. SMV1235-011 Capacitance vs Voltage (7.575/[1–VV/0.8]0.45) Copyright © 2005, 2010, 2015 Skyworks Solutions, Inc. All Rights Reserved. Information in this document is provided in connection with Skyworks Solutions, Inc. (“Skyworks”) products or services. These materials, including the information contained herein, are provided by Skyworks as a service to its customers and may be used for informational purposes only by the customer. Skyworks assumes no responsibility for errors or omissions in these materials or the information contained herein. Skyworks may change its documentation, products, services, specifications or product descriptions at any time, without notice. Skyworks makes no commitment to update the materials or information and shall have no responsibility whatsoever for conflicts, incompatibilities, or other difficulties arising from any future changes. 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Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 200315C • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • August 5, 2015 5