Skip to end of metadataGo to start of metadata

1. Pspice Mosfet Kp
2. Mosfet Kp Parameter
3. Nmos Spice Model
4. Kp Mosfet Online

On This Page

Level 1 MOSFET model.MODEL MODN NMOS LEVEL=1 VTO=1 KP=50U LAMBDA=.033 GAMMA=.6 + PHI=0.8 TOX=1.5E-10 CGDO=5E-10 CGSO= 5e-10 CJ=1E-4 CJSW=5E-10 + MJ=0.5 PB=0.95 The Level 1 model is adequate for channel lengths longer than about 1.5 µm For sub-µm MOSFETs, BSIM = “Berkeley Short-Channel IGFET Model” developed by Profs.

KP 1 0 mA/V274 Note that the voltage gain is off by a large percentage. The explanation of this difference is the value used for KP! For hand calculations we used KP=100 mA/V2, but using KP=74 mA/V2, it leads to a gm=4.4 mA/V and the voltage gain is around -4.4 V/V. MOSFET (M1) and then, on the edit menu, select “Edit PSpice Model”. What we want to put into the model are values of K n and V TN appropriate to the 2N7000. The edit box is shown, as modified, as Figure 3. You need to know what to call the parameters you want to change.

LEVEL1_Model (MOSFET Level-1 Model)

Symbol

Available in ADS and RFDE

Supported via model include file in RFDE

Parameters

Model parameters must be specified in SI units.

Netlist Format

Model statements for the ADS circuit simulator may be stored in an external file. This is typically done with foundry model kits. For more information on how to set up and use foundry model kits, refer to Design Kit Development.

model modelname MOSFET Idsmod=1 [parm=value]*

The model statement starts with the required keyword model. It is followed by the modelname that will be used by mosfet components to refer to the model. The third parameter indicates the type of model; for this model it is MOSFET. Idsmod=1 is a required parameter that is used to tell the simulator to use the Spice level 1 equations. Use either parameter NMOS=yes or PMOS=yes to set the transistor type. The rest of the model contains pairs of model parameters and values, separated by an equal sign. The name of the model parameter must appear exactly as shown in the parameters table-these names are case sensitive. Some model parameters have aliases, which are listed in parentheses after the main parameter name; these are parameter names that can be used instead of the primary parameter name. Model parameters may appear in any order in the model statement. Model parameters that are not specified take the default value indicated in the parameters table. For more information about the ADS circuit simulator netlist format, including scale factors, subcircuits, variables and equations, refer to 'ADS Simulator Input Syntax' in Using Circuit Simulators.

Example:

Notes/Equations

Note

For RFDE Users Information about this model must be provided in a model file; refer to Netlist Format.

1. The simulator provides three MOSFET device models that differ in formulation of I-V characteristics. MOSFET Level1_Model is Shichman-Hodges model derived from [1].
2. Vto, Kp, Gamma, Phi, and Lambda determine the DC characteristics of a MOSFET device. ADS will calculate these parameters (except Lambda) if instead of specifying them, you specify the process parameters Tox, Uo, Nsub, and Nss.
3. Vto is positive (negative) for enhancement mode and negative (positive) for depletion mode N-channel (P-channel) devices.
4. P-N junctions between the bulk and the drain and the bulk and the source are modeled by parasitic diodes. Each bottom junction is modeled by a diode and each periphery junction is modeled by a depletion capacitance.
5. Diode parameters for the bottom junctions can be specified as absolute values (Is, Cbd and Cbs) or as per unit junction area values (Js and Cj).
   If Cbd = 0.0 and Cbs = 0.0, then Cbd and Cbs will be calculated:

   Cbd = Cj Ad, Cbs = Cj As

   If Js > 0.0 and Ad > 0.0 and As > 0.0, then Is for drain and source will be calculated:

   Is(drain) = Js Ad, Is(source) = Js As

6. Drain and source ohmic resistances can be specified as absolute values (Rd, Rs) or as per unit square value (Rsh).
   If Nrd 0.0 or Nrs 0.0, Rd and Rs will be calculated:
   Rd = Rsh Nrd, Rs = Rsh Nrs
7. Charge storage in the MOSFET consists of capacitances associated with parasitics and intrinsic device.
   Parasitic capacitances consist of three constant overlap capacitances (Cgdo, Cgso, Cgbo) and the depletion layer capacitances for both substrate junctions (divided into bottom and periphery), that vary as Mj and Mjsw power of junction voltage, respectively, and are determined by the parameters Cbd, Cbs, Cj, Cjsw, Mj, Mjsw, Pb and Fc.
   The intrinsic capacitances consist of the nonlinear thin-oxide capacitance, which is distributed among the gate, drain, source, and bulk regions.
   
8. Charge storage is modeled by fixed and nonlinear gate and junction capacitances. MOS gate capacitances, as a nonlinear function of terminal voltages, are modeled by Meyer's piece-wise linear model for levels 1, 2, and 3. The Ward charge conservation model is also available for levels 2 and 3, by specifying the XQC parameter to a value smaller than or equal to 0.5. For Level 1, the model parameter TOX must be specified to invoke the Meyer model when Capmod is equal to 1 (default value). If Capmod = 0, no gate capacitances will be calculated. If Capmod = 2, a smooth version of the Meyer model is used. If Capmod =3, the charge conserving first-order MOS charge model [2] that was used in Libra is used.
9. To include the thin-oxide charge storage effect, model parameter Tox must
   be > 0.0.
10. Imax and Imelt Parameters
    Imax and Imelt specify the P-N junction explosion current. Imax and Imelt can be specified in the device model or in the Options component; the device model value takes precedence over the Options value.
    If the Imelt value is less than the Imax value, the Imelt value is increased to the Imax value.
    If Imelt is specified (in the model or in Options) junction explosion current = Imelt; otherwise, if Imax is specified (in the model or in Options) junction explosion current = Imax; otherwise, junction explosion current = model Imelt default value (which is the same as the model Imax default value).
11. Use AllParams with a DataAccessComponent to specify file-based parameters (refer to 'DataAccessComponent' in Introduction to Circuit Components). Note that model parameters that are explicitly specified take precedence over those specified via AllParams. Set AllParams to the DataAccessComponent instance name.

Temperature Scaling

The model specifies Tnom, the nominal temperature at which the model parameters were calculated or extracted. To simulate the device at temperatures other than Tnom, several model parameters must be scaled with temperature. The temperature at which the device is simulated is specified by the device item Temp parameter. (Temperatures in the following equations are in Kelvin.)
The depletion capacitances Cbd, Cbs, Cj, and Cjsw vary as:

where γ is a function of the junction potential and the energy gap variation with temperature.

The surface potential Phi and the bulk junction potential Pb vary as:

The transconductance Kp and mobility Uo vary as:

The source and drain to substrate leakage currents Is and Js vary as:

where E_G is the silicon bandgap energy as a function of temperature.
The MOSFET threshold voltage variation with temperature is given by:

Noise Model

Thermal noise generated by resistor Rg, Rs, Rd, and Rds is characterized by the following spectral density:

Channel and flicker noise (Kf, Af, Ffe) generated by DC transconductance g_m and current flow from drain to source is characterized by spectral density:

In the preceding expressions, k is Boltzmann's constant, T is operating temperature in Kelvin, q is electron charge, kf , a f, and f fe are model parameters, f is simulation frequency, and Δ f is noise bandwidth.

Pspice Mosfet Kp

References

1. H. Shichman and D. A. Hodges. 'Modeling and simulation of insulated-gate field-effect transistor switching circuits,' IEEE Journal of Solid-State Circuits, SC-3, 285, Sept. 1968.
2. Karen A. Sakallah, Yao-tsung Yen, and Steve S. Greenberg. 'The Meyer Model Revisited: Explaining and Correcting the Charge Non-Conservation Problem,' ICCAD , 1987.
3. P. Antognetti and G. Massobrio. Semiconductor device modeling with SPICE , New York: McGraw-Hill, Second Edition 1993.

Equivalent Circuit

• Basic Electronics Tutorial

• Electronic Components

• Resistors

• Capacitors

• Inductors
• Transformers
• Diodes
• Transistors
• Basic Electronics Useful Resources
• Selected Reading

FETs have a few disadvantages like high drain resistance, moderate input impedance and slower operation. To overcome these disadvantages, the MOSFET which is an advanced FET is invented.

MOSFET stands for Metal Oxide Silicon Field Effect Transistor or Metal Oxide Semiconductor Field Effect Transistor. This is also called as IGFET meaning Insulated Gate Field Effect Transistor. The FET is operated in both depletion and enhancement modes of operation. The following figure shows how a practical MOSFET looks like.

Construction of a MOSFET

The construction of a MOSFET is a bit similar to the FET. An oxide layer is deposited on the substrate to which the gate terminal is connected. This oxide layer acts as an insulator (sio₂ insulates from the substrate), and hence the MOSFET has another name as IGFET. In the construction of MOSFET, a lightly doped substrate, is diffused with a heavily doped region. Depending upon the substrate used, they are called as P-type and N-type MOSFETs.

The following figure shows the construction of a MOSFET.

The voltage at gate controls the operation of the MOSFET. In this case, both positive and negative voltages can be applied on the gate as it is insulated from the channel. With negative gate bias voltage, it acts as depletion MOSFET while with positive gate bias voltage it acts as an Enhancement MOSFET.

Classification of MOSFETs

Depending upon the type of materials used in the construction, and the type of operation, the MOSFETs are classified as in the following figure.

After the classification, let us go through the symbols of MOSFET.

The N-channel MOSFETs are simply called as NMOS. The symbols for N-channel MOSFET are as given below.

The P-channel MOSFETs are simply called as PMOS. The symbols for P-channel MOSFET are as given below.

Now, let us go through the constructional details of an N-channel MOSFET. Usually an NChannel MOSFET is considered for explanation as this one is mostly used. Also, there is no need to mention that the study of one type explains the other too.

Construction of N- Channel MOSFET

Let us consider an N-channel MOSFET to understand its working. A lightly doped P-type substrate is taken into which two heavily doped N-type regions are diffused, which act as source and drain. Between these two N+ regions, there occurs diffusion to form an Nchannel, connecting drain and source.

A thin layer of Silicon dioxide (SiO₂) is grown over the entire surface and holes are made to draw ohmic contacts for drain and source terminals. A conducting layer of aluminum is laid over the entire channel, upon this SiO₂ layer from source to drain which constitutes the gate. The SiO₂ substrate is connected to the common or ground terminals.

Because of its construction, the MOSFET has a very less chip area than BJT, which is 5% of the occupancy when compared to bipolar junction transistor. This device can be operated in modes. They are depletion and enhancement modes. Let us try to get into the details.

Working of N - Channel (depletion mode) MOSFET

For now, we have an idea that there is no PN junction present between gate and channel in this, unlike a FET. We can also observe that, the diffused channel N (between two N+ regions), the insulating dielectric SiO₂ and the aluminum metal layer of the gate together form a parallel plate capacitor.

If the NMOS has to be worked in depletion mode, the gate terminal should be at negative potential while drain is at positive potential, as shown in the following figure.

When no voltage is applied between gate and source, some current flows due to the voltage between drain and source. Let some negative voltage is applied at V_GG. Then the minority carriers i.e. holes, get attracted and settle near SiO₂ layer. But the majority carriers, i.e., electrons get repelled.

With some amount of negative potential at V_GG a certain amount of drain current I_D flows through source to drain. When this negative potential is further increased, the electrons get depleted and the current I_D decreases. Hence the more negative the applied V_GG, the lesser the value of drain current I_D will be.

Mosfet Kp Parameter

The channel nearer to drain gets more depleted than at source (like in FET) and the current flow decreases due to this effect. Hence it is called as depletion mode MOSFET.

Working of N-Channel MOSFET (Enhancement Mode)

Nmos Spice Model

The same MOSFET can be worked in enhancement mode, if we can change the polarities of the voltage V_GG. So, let us consider the MOSFET with gate source voltage V_GG being positive as shown in the following figure.

When no voltage is applied between gate and source, some current flows due to the voltage between drain and source. Let some positive voltage is applied at V_GG. Then the minority carriers i.e. holes, get repelled and the majority carriers i.e. electrons gets attracted towards the SiO₂ layer.

With some amount of positive potential at V_GG a certain amount of drain current I_D flows through source to drain. When this positive potential is further increased, the current I_D increases due to the flow of electrons from source and these are pushed further due to the voltage applied at V_GG. Hence the more positive the applied V_GG, the more the value of drain current I_D will be. The current flow gets enhanced due to the increase in electron flow better than in depletion mode. Hence this mode is termed as Enhanced Mode MOSFET.

P - Channel MOSFET

The construction and working of a PMOS is same as NMOS. A lightly doped n-substrate is taken into which two heavily doped P+ regions are diffused. These two P+ regions act as source and drain. A thin layer of SiO₂ is grown over the surface. Holes are cut through this layer to make contacts with P+ regions, as shown in the following figure.

Working of PMOS

When the gate terminal is given a negative potential at V_GG than the drain source voltage V_DD, then due to the P+ regions present, the hole current is increased through the diffused P channel and the PMOS works in Enhancement Mode.

When the gate terminal is given a positive potential at V_GG than the drain source voltage V_DD, then due to the repulsion, the depletion occurs due to which the flow of current reduces. Thus PMOS works in Depletion Mode. Though the construction differs, the working is similar in both the type of MOSFETs. Hence with the change in voltage polarity both of the types can be used in both the modes.

This can be better understood by having an idea on the drain characteristics curve.

Drain Characteristics

The drain characteristics of a MOSFET are drawn between the drain current I_D and the drain source voltage V_DS. The characteristic curve is as shown below for different values of inputs.

Actually when V_DS is increased, the drain current I_D should increase, but due to the applied V_GS, the drain current is controlled at certain level. Hence the gate current controls the output drain current.

Kp Mosfet Online

Transfer Characteristics

Transfer characteristics define the change in the value of V_DS with the change in I_D and V_GS in both depletion and enhancement modes. The below transfer characteristic curve is drawn for drain current versus gate to source voltage.

Comparison between BJT, FET and MOSFET

Now that we have discussed all the above three, let us try to compare some of their properties.

So far, we have discussed various electronic components and their types along with their construction and working. All of these components have various uses in the electronics field. To have a practical knowledge on how these components are used in practical circuits, please refer to the ELECTRONIC CIRCUITS tutorial.