(1)AIM: As a result, this operating region is chosen

(1)AIM: To get familiarized with NMOSFET
Characteristics of 180nm channel width and natures of              graphs.

(2)SOFTWARE REQUIRED: Cadence

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(3)THEORY:

Ø 
MOSFET:The
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-

1.     
Cut-Off Region-
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.

 

2.     
Ohmic/Linear Region
-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.

 

3.     
Saturation Region-In
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.

 

Ø 
ON-CURRENT-The
current in the circuit on application of Maximum Voltage i.e. Vgs=1.8V.

 

Ø 
OFF-CURRENT-
The current in the circuit at Vgs=0V.

 

Ø 
THRESHOD
VOLTAGE-The threshold
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.. 

 

 

 

 

(4)PROCEDURE:

Using
the Cadence software we plot the graphs of NMOSFET.

·        
Open
the terminal and enter the following commands to get started. The commands are:

1.csh

2.source  /cad/cshrc1

3.virtuoso&

·        
These
steps lead us to the corresponding window where we can design the circuit of
MOSFET.

·        
The
next step is to create a new library. For this, follow the following steps:

File
-> library -> enter the name of your library (also select the option
“select library from latest technology” -> ok

 

·        
Then
create a cellview. For this follow the steps:

File ->cellview
and select the name of your library (you gave).

 

·        
To
add components, go to create->instance->browse

Select the required
components.

1.     
NMOS-

Library->select
gpdk180

              Cell->select nmos

              View-> select symbol

FIG-1:SELECTION
OF gpdk180

 

2.     
POWER
SUPPLY- Now, to add power supply , under library select analoglib.

undercell, select vdc
and under view- select default

 

FIG-2: SELECTION OF POWER SUPPLY

FIG-3:
PROPERTIES OF VOLTAGE

 

 

3.     
GND-
Using analogLib ,gnd was added similarly.

FIG-4:
SELECTION OF GND

 

FIG-5:
CIRCUIT DIAGRAM

After
this the graphs were plotted. The steps to be followed are-

·        
Launch->ADEL->Analyses->Choose->dc->select
component

·        
The
voltage given was 0-1.8V.

·        
This
was done to select for x-axis.

·        
Now,
Outputs->To Be Plotted->Select in the Design

·        
The
Run command was executed to plot graphs.

 

 

FIG-6:
ADEL WINDOW

 

 

 (5) RESULTS:

1.     
We
get a graph like this between Vds and Id:

FIG-7: GRAPH OF Vds
Vs

 2. We can also plot multiple steps. The
following 2 screenshots show us how it happens.

 

 

 

 

 

                                             
FIG-8: GRAPH FOR MULTIPLE VALUES

 

 

3.
GRAPH OF Vgs VS Id:

Follow
the same steps as above. Only the difference is when the component is selected.

This
time select the Vgs as the component.

This
leads us to the following graph:

FIG-9: GRAPH OF VgsVs Id

 

(6)CALCULATIONS:

1.  On current: Maximum value of Vdd .Here the
value is 2.3303mA.

FIG-10:
ON CURRENT

 

2.
Off current: This is the value where Vgs=0. Here it is 23.5418 pA.

FIG-11:
OFF CURRENT

3.Threshold:
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
CALCULATION

 

4.Subthreshold
swing: Difference between  Vgs Vs Id
value per decade.

Eg:
10^-8 => v=212.128mV

10^-7=>v=289.856mV

The
difference gives the sub-threshold swing.

                                  FIG-13: GRAPH FOR CALCULATION OF
SUBTHRESHOLD SWING

5.Ion
/ I off= 2.3303mA/23.5418pA

(7)CONCLUSION: In this way, we study about MOSFET
Characterization using Cadence.

(8)ERROR:

   To open Cadence, we used the usual command
of – source cad/cshrc_new. But this command didn’t work for virtually installed
cadence.

Using,
source cad/cshrc1 helped us to rectify the issue.