(1)AIM: To get familiarized with NMOSFET
Characteristics of 180nm channel width and natures of graphs.
(2)SOFTWARE REQUIRED: Cadence
metal–oxide–semiconductor field-effect transistor (MOSFET) is a transistor used
for amplifying or switching electronic signals. In MOSFETs, a voltage on the
oxide-insulated gate electrode can induce a conducting channel between the two
other contacts called source and drain. The channel can be of n-type or p-type,
and is accordingly called an nMOSFET or a P-MOSFET.
In general, any MOSFET is seen to
exhibit three operating regions-
Cut-off region is a region in which the MOSFET will be OFF as there will be
no current flow
through it. In this region, MOSFET behaves like an open switch and is thus used
when they are required to function as electronic switches.
-Ohmic or linear region is a region where in the current IDS increases
with an increase in the value of VDS. When MOSFETs are made to
operate in this region, they can be used as amplifiers.
saturation region, the MOSFETs have their IDS constant inspite
of an increase in VDS and occurs once VDSexceeds the
value of pinch-off voltage VP.
Under this condition, the device will act like a closed switch through which a
saturated value of IDS flows. As a result, this operating
region is chosen whenever MOSFETs are required to perform switching operations.
current in the circuit on application of Maximum Voltage i.e. Vgs=1.8V.
The current in the circuit at Vgs=0V.
voltage, also called the gate
voltage, commonly abbreviated as Vth or VGS (th),
of a field-effect transistor (FET) is
the minimum gate-to-source voltage differential that is needed to create a
conducting path between the source and drain terminals.
Ø SUBTHRESHOLD SWING- The
subthreshold swing is defined as
the gate voltage required. to change the drain current by one order of
magnitude, one. decade..
the Cadence software we plot the graphs of NMOSFET.
the terminal and enter the following commands to get started. The commands are:
steps lead us to the corresponding window where we can design the circuit of
next step is to create a new library. For this, follow the following steps:
-> library -> enter the name of your library (also select the option
“select library from latest technology” -> ok
create a cellview. For this follow the steps:
and select the name of your library (you gave).
add components, go to create->instance->browse
Select the required
View-> select symbol
SUPPLY- Now, to add power supply , under library select analoglib.
undercell, select vdc
and under view- select default
FIG-2: SELECTION OF POWER SUPPLY
PROPERTIES OF VOLTAGE
Using analogLib ,gnd was added similarly.
SELECTION OF GND
this the graphs were plotted. The steps to be followed are-
voltage given was 0-1.8V.
was done to select for x-axis.
Outputs->To Be Plotted->Select in the Design
Run command was executed to plot graphs.
get a graph like this between Vds and Id:
FIG-7: GRAPH OF Vds
2. We can also plot multiple steps. The
following 2 screenshots show us how it happens.
FIG-8: GRAPH FOR MULTIPLE VALUES
GRAPH OF Vgs VS Id:
the same steps as above. Only the difference is when the component is selected.
time select the Vgs as the component.
leads us to the following graph:
FIG-9: GRAPH OF VgsVs Id
1. On current: Maximum value of Vdd .Here the
value is 2.3303mA.
Off current: This is the value where Vgs=0. Here it is 23.5418 pA.
This is that value where the curve meets the value of Id. Here the value of Id
is 2.2mV.(Calculated by the formula Id=0.1uA*W/l)
FIG-12: THRESHOLD VOLTAGE
swing: Difference between Vgs Vs Id
value per decade.
10^-8 => v=212.128mV
difference gives the sub-threshold swing.
FIG-13: GRAPH FOR CALCULATION OF
/ I off= 2.3303mA/23.5418pA
(7)CONCLUSION: In this way, we study about MOSFET
Characterization using Cadence.
To open Cadence, we used the usual command
of – source cad/cshrc_new. But this command didn’t work for virtually installed
source cad/cshrc1 helped us to rectify the issue.