- You can see that the cross section of the Mosfet is EVEN from the center vertical line. So, whichever (out of the two terminals on sides of nmos) terminal has higher voltage than the other terminal, that becomes your drain (for NMOS) and the other terminal with lower voltage becomes the source (for nmos). The reverse is followed for pmos.
- Detailed Description: Pack of 10 IRFZ48N FET Transistor Type: NMOS Vds: 50V Rds: 0.014 Ohms Ids: 64A Pd: 130W Case: TO-262 (DPAK) WT.05/Pack of 10.
MOSFET TRANSISTOR SUMMARY NMOS Transistor (p. 249): NMOS Cross-section (p.
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The following information describes how the various MOSFET models from SPICE and Spectre are translated to the corresponding ADS models.
SPICE Models
All Mosfet devices in SPICE reference a model by its instance name. Each Mosfet model in SPICE has a keyword NMOS or PMOS, as well as a Level parameter.
The NMOS/PMOS keyword is used to determine what device to place in the schematic, MOSFET_NMOS or MOSFET_PMOS. The Level is used to determine which model is placed and what value is set for Idsmod.
In the ADS netlist, the model is always called MOSFET, with the appropriate keywords NMOS and PMOS set to [0|1], and the parameter Idsmod set as specified in the following table.
The only exception to this is the Mosfet device which refers to an HSpice Level 50 model, the Phillips MOS9 model. In this case, the device placed in the schematic will be MM9_NMOS or MM9_PMOS and the model will be MOS_Model9_Process. The netlist component is called MOS9. For both the MM9_NMOS and the MM9_PMOS, the translator sets the parameter Type=2 to indicate that it is a process-based model.
SPICE Level Parameters Mapping Table (MOSFET)
Spice2/3 Level | PSpice Level | HSpice Level | ADS Schematic Model | ADS Netlist Idsmod | ADS BSIM3 Version |
|---|---|---|---|---|---|
1 | 1 | 1 | LEVEL1_Model | 1 | |
2 | 2 | 2 | LEVEL2_Model | 2 | |
3 | 3 | 3 | LEVEL3_Model | 3 | |
4 | 4 | 13, 28 | BSIM1_Model | 4 | |
5 | - | 39 | BSIM2_Model | 5 | |
7 | BSIM3_Model | 8 | 3.1 | ||
49, 53 | BSIM3_Model | 8 | legal BSIM3 Versions are: 3.0, 3.1, 3.2, 3.21, and 3.22 |
Dependence Parameters
There are certain model parameters listed in the BSIM Models that reference additional parameters. These additional parameters are denoted in parenthesis using the letters L, W and/or P. As an example, the Dwg (L,W, P) parameter in the BSIM3 Model defines four separate parameters:
- Dwg: Coefficient of Weff's gate dependence
- LDwg: Length dependence of Dwg
- WDwg: Width dependence of Dwg
- PDwg: Cross dependence of Dwg
Each letter indicates a sensitivity parameter that exists in HSpice and ADS. These parameters are length(L), Width(W) and Cross(P). Refer to your HSpice and ADS component documentation for details.
HSpice Automatic Model Selection
Automatic Model Selection, also known as binning, is an HSpice feature that allows for the definition of a library of Mosfets over a range of lengths and widths. The following netlist fragment is an example of automatic model selection in HSpice. It is currently used only for Mosfets. Notice that the model name is a root name plus an extension, separated by a period (that is: NCHAN.2). Also note the special model parameters, LMIN, LMAX, WMIN and WMAX. They are used only for automatic model selection.
The ADS equivalent of this functionality is provided by a component called BinModel. Since ADS component names cannot include a period, the models are renamed nchanx2 and nchanx3. Then a BinModel component is placed, which lists the models by name, as well as listing the special length and width parameter ranges, as defined by LMIN, LMAX, WMIN and WMAX. The name of the BinModel component is the same as the root name of the models, in this case nchan. The ranges of all models with the same root name will be recorded on one BinModel component as shownin the following figure.
The ADS BinModel Component
Also note that the Mosfet devices that are placed in the schematic do not refer to the Mosfet models as they normally would. Instead they refer to the BinModel. During simulation, the length and width specified on the device are sent to the BinModel and checked against the ranges specified for each model, to determine which model to use. If the length and width on the device fall within the range of the length and width on more than one model, the first one that matches is used.
Spectre Models
All Mosfet devices in Spectre reference a model by its instance name. Each Mosfet model in Spectre has a name value pair type=[n|p].
The type value pair keyword is used to determine what device to place in the schematic, MOSFET_NMOS or MOSFET_PMOS. The Level is used to determine which model is placed and what value is set for Idsmod.
In the ADS netlist, the model is always called MOSFET, with the appropriate keywords NMOS and PMOS set to [0|1], and the parameter Idsmod set as specified in the following table.
The only exception to this is the Mosfet device which refers to the Phillips MOS902 model. In this case, the device placed in the schematic will be MM9_NMOS or MM9_PMOS and the model will be MOS_Model9_Process. The netlist component is called MOS9. For both the MM9_NMOS and the MM9_PMOS, the translator sets the parameter Type=2 to indicate that it is a process-based model.
Spectre Level Parameters Mapping (MOSFET)
Spectre Model | Supported | ADS Schematic Model | ADS Netlist Idsmod Drivers gale banks engineering usb devices. | ADS BSIM3 Version |
|---|---|---|---|---|
mos0 | NO | Not Translated | ||
mos1 | YES | LEVEL1_Model | 1 | |
mos15 | NO | Not Translated | ||
mos2 | YES | LEVEL 2_Model | 2 | |
mos3 | YES | LEVEL3_Model | 3 | |
mos30 | NO | Not Translated | ||
mos3002 | NO | Not Translated | ||
mos705 | NO | Not Translated | ||
mos902 | YES | MOS_Model9_Process | N/A | |
mos903 | NO | Dragonrise driver download. Not Translated | ||
bsim3v3 | YES | BSIM3_Model | 8 | 3.22 |
b3soi-pd | YES | BSIM3SOI_Model |
Dependence Parameters
There are certain model parameters listed in the BSIM Models that reference additional parameters. These additional parameters are denoted in parenthesis using the letters L, W and/or P. As an example, the Dwg (L,W, P) parameter in the BSIM3 Model defines four separate parameters:
- Dwg: Coefficient of Weff's gate dependence.
- LDwg: Length dependence of Dwg.
- WDwg: Width dependence of Dwg.
- PDwg: Cross dependence of Dwg.
Each letter indicates a sensitivity parameter that exists in Spectre and ADS. These parameters are length(L), Width(W) and Cross(P). Refer to your Spectre and ADS component documentation for details.
The following MOSFET models are translated in ADS:
Binning Process
In order for ADS to translate the binning process, each binning definition is translated as a separate model.
Binning Example
The following is an example Spectre binning statement for a bsim model:
The Netlist Translator separates each binning reference into an ADS model. The example would result in three models with the names ModelName_1, ModelName_2, and ModelName_3. The models are then tied together by creating an ADS 'BinModel' component and configuring the appropriate min/max values.
Let’s talk about the basics of MOSFET and how to use them. This tutorial is written primarily for non-academic hobbyists, so I will try to simplify the concept and focus more on the practical side of things.
However if you are into how MOSFET work, I will share some useful academic articles and resources at the end of this post. MOSFET has some advantage and disadvantage over BJT, so choose carefully base on your application.
You can buy MOSFET’s for Arduino Projects on Amazon: http://amzn.to/2Gk6ruW
N Mosfet Circuit
MOSFET stands for metal-oxide semiconductor field-effect transistor. It is a special type of field-effect transistor (FET).
Unlike BJT which is ‘current controlled’, the MOSFET is a voltage controlled device. The MOSFET has “gate“, “Drain” and “Source” terminals instead of a “base”, “collector”, and “emitter” terminals in a bipolar transistor. By applying voltage at the gate, it generates an electrical field to control the current flow through the channel between drain and source, and there is no current flow from the gate into the MOSFET.
A MOSFET may be thought of as a variable resistor, where the Gate-Source voltage difference can control the Drain-Source Resistance. When there is no applying voltage between the Gate-Source , the Drain-Source resistance is very high, which is almost like a open circuit, so no current may flow through the Drain-Source. When Gate-Source potential difference is applied, the Drain-Source resistance is reduced, and there will be current flowing through Drain-Source, which is now a closed circuit.
In a nutshell, a FET is controlled by the Gate-Source voltage applied (which regulates the electrical field across a channel), like pinching or opening a straw and stopping or allowing current flowing. Because of this property, FETs are great for large current flow, and the MOSFET is commonly used as a switch.
Okay, let me summarize the differences between BJT and MOSFET.
- Unlike bipolar transistors, MOSFET is voltage controlled. While BJT is current controlled, the base resistor needs to be carefully calculated according to the amount of current being switched. Not so with a MOSFET. Just apply enough voltage to the gate and the switch operates.
- Because they are voltage controlled, MOSFET have a very high input impedance, so just about anything can drive them.
- MOSFET has high input impedence.
To use a MOSFET as a switch, you have to have its gate voltage (Vgs) higher than the source. If you connect the gate to the source (Vgs=0) it is turned off.
For example we have a IRFZ44N which is a “standard” MOSFET and only turns on when Vgs=10V – 20V. But usually we try not to push it too hard so 10V-15V is common for Vgs for this type of MOSFET.
However if you want to drive this from an Arduino which is running at 5V, you will need a “logic-level” MOSFET that can be turned on at 5V (Vgs = 5V). For example, the ST STP55NF06L. You should also have a resistor in series with the Arduino output to limit the current, since the gate is highly capacitive and can draw a big instantaneous current when you try to turn it on. Around 220 ohms is a good value.
This page shows some detail explanation how a MOSFET works as a switch. This page shows some advanced usage of MOSFET.
MOSFETs come in four different types. There are three main categories we need to know.
- N-Channel (NMOS) or P-Channel (PMOS)
- Enhancement or Depletion mode
- Logic-Level or Normal MOSFET
N-Channel – For an N-Channel MOSFET, the source is connected to ground. To turn the MOSFET on, we need to raise the voltage on the gate. To turn it off we need to connect the gate to ground.
P-Channel – The source is connected to the power rail (Vcc). In order to allow current to flow the Gate needs to be pulled to ground. To turn it off the gate needs to be pulled to Vcc.
Depletion Mode – It requires the Gate-Source voltage ( Vgs ) applied to switch the device “OFF”.
Pmos Vs Nmos Symbol
Enhancement Mode – The transistor requires a Gate-Source voltage ( Vgs ) applied to switch the device “ON”.
Despite the variety, the most commonly used type is N-channel enhancement mode.
There are also Logic-Level and Normal MOSFET, but the only difference is the Gate-Source potential level required to drive the MOSFET.
I will try to explain it in the simplest way I can, for more detail or if you are in doubt, check the references and links I provide at the bottom of the post.
MOSFET is a voltage controlled field effect transistor that differs from a JFET. The Gate electrode is electrically insulated from the main semiconductor by a thin layer of insulating material (glass, seriously!). This insulated metal gate is like a plate of a capacitor which has an extremely high input resistance (as high as almost infinite!). Because of the isolation of the Gate there is no current flow into the MOSFET from Gate.
N Mosfet Operation
When voltage is applied at the gate, it changes the width of the Drain-Source channel along which charge carriers flow (electron or hole). The wider the channel, the better the device conducts.
The MOSFET are used differently compared to the conventional junction FET.
- The infinite high input impedance makes MOSFETs useful for power amplifiers. The devices are also well suited to high-speed switching applications. Some integrated circuits contain tiny MOSFETs and are used in computers.
- Because the oxide layer is so thin, the MOSFET can be damaged by built up electrostatic charges. In weak-signal radio-frequency work, MOSFET devices do not generally perform as well as other types of FET.
Where to put the load to a MOSFET? Source or Drain?
Because load has resistance, which is basically a resitor. For N-channel MOSFET the reason we usually put the load at the Drain side is because of the Source is usually connected to GND.
If load is connected at the source side, the Vgs will needs to be higher in order to switch the MOSFET, or there will be insufficient current flow between source and drain than expected.
Heat Sink connected to the Drain?
Typically the heat sink on the back of a MOSFET is connected to the Drain! If you mount multiple MOSFETs on a heat sink, they must be electrically isolated from the heat sink! It’s good practice to isolate regardless in case the heat sink is bolted to a grounding frame.
What is the Body Diode For?
Mosfet Transistor
MOSFETs also have an internal diode which may allow current to flow unintentionally. The body diode will also limit switching speed. You don’t have to worry about it if you are operating under 1Mhz.
Nmos Transistor
- Theory behind MOSFET (Youtube Video Lecture)
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