DC analysis of MOSFET circuits

In the circuit shown in the figure, the device parameters are $L_p=L_n=2\,\mu$m, $W_n=5\,\mu$m, $\mu _n C_{ox}=20\,\mu A/V^2$, $\mu _p C_{ox}=8\,\mu A/V^2$, $\lambda=0\,V^{-1}$. Find $W_p$ for a drain current of $5.57\,\mu$A. What is $V_1$ in that situation?

(Assume the long-channel MOSFEL model to be valid.)

In [1]:
from IPython.display import Image
Image(filename =r'EC_mos_dc_1_fig_1.png', width=100)
Out[1]:
No description has been provided for this image
In [2]:
# run this cell to view the circuit file.
%pycat EC_mos_dc_1_orig.in

We now replace the string \$Wp with the value of our choice by running the python script given below. It takes an existing circuit file EC_mos_dc_1_orig.in and produces a new circuit file EC_mos_dc_1.in, after replacing \$Wp with the value of our choice.

In [3]:
import gseim_calc as calc
s_Wp = '5u' # to be changed by user

l = [
  ('$Wp', s_Wp),
]
calc.replace_strings_1("EC_mos_dc_1_orig.in", "EC_mos_dc_1.in", l)
print('EC_mos_dc_1.in is ready for execution')

EC_mos_dc_1.in is ready for execution
Execute the following cell to run NGSPICE on EC_mos_dc_1.in.
In [4]:
import ngspice_calc as ngcalc
ngcalc.run_ngspice('EC_mos_dc_1.in')

Circuit: * dc analysis using basic mosfet model

Doing analysis at TEMP = 27.000000 and TNOM = 27.000000

No. of Data Columns : 2  

No. of Data Rows : 1

Total analysis time (seconds) = 0

Total elapsed time (seconds) = 0.002 

Total DRAM available = 7739.719 MB.
DRAM currently available = 2456.102 MB.
Total ngspice program size =   19.590 MB.
Resident set size =    8.996 MB.
Shared ngspice pages =    7.609 MB.
Text (code) pages =    5.789 MB.
Stack = 0 bytes.
Library pages =    1.840 MB.
Out[4]:
'EC_mos_dc_1.raw'
In [5]:
# get output file information from the circuit file
s = ngcalc.slv('EC_mos_dc_1.in')

for i in range(s.num_plots()):
    print(f"  plot {i}: {s.plotname(i)} | type: {s.analysis_type(i)} | vars: {s.variables(i)}")

  plot 0: Operating Point | type: op | vars: ['v(1)', 'i(vdd)']
In [6]:
V1 = s.get_array('v(1)')[0]
I  = s.get_array('i(vdd)')[0]

print(f'V1 = {V1:7.4f} V')
print(f'current = {-I:11.4e} A')

V1 =  1.3874 V
current =  3.7528e-06 A

This notebook was contributed by Prof. M. B. Patil, IIT Bombay. He may be contacted at mbpatil@ee.iitb.ac.in.

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