EE204: Analog Circuits
Tutorial 5
Dept. of Electrical Engineering, IIT Bombay
Autumn Semester 2023
13-09-2023
Q1.
In Figure a, The MOSFET is specified to have Vt = 1 V and knW/L = 1 mA/V2. Assume λ = 0,
VDD =15 V,Rs=Rd=10K Ohms.
(a) Bias the circuit so that the DC drain current is ID = 0.5 mA.
(b) Calculate the percentage change in the value of ID obtained when the MOSFET is
replaced with another unit having Vt = 1.5 V for the same bias conditions.
(a)
(b)
Q2.
For the circuit shown in Figure b, Determine the following
(a)
(b)
(c)
(d)
Drain current,
small-signal voltage gain
input resistance,
largest allowable input signal
Given , VDD = 15 V, RD = 10k, kn = 0.25 mA/V2 , and Vt = 1.5 V, g0=21.2uS.
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Q3.
The NMOS transistor-based amplifier, shown in the figure below, Given Vt = 0.7 V.
(a) Neglecting the Early effect, verify that the MOSFET is operating in saturation with
ID = 0.5 mA and VOV = 0.3 V.
What must the MOSFET’s kn be? What is the DC
voltage at the drain?
(b) Find Rin,Gm and Vo/Vsig (assume g0=10uS)
(c) If vsig is a sinusoid with a peak amplitude ‘x’,
find the maximum allowable value of ‘x’ for
which the transistor remains in saturation. What
is the corresponding amplitude of the output
voltage?
(d) What is the value of resistance Rs that needs
to be inserted in series with capacitor CS in order
to allow us to double the input signal ‘x’? What
output voltage now results?
Q4.
i. Consider the circuits given below with ideal opamps to evaluate the expression of Iout in
terms of Vin and Vo (and resistances).
(a)
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(b)
ii. For the above circuits to be current sources Driving Iout into Load(R_L) from Node Vout,
Derive the constraints on the resistances and also evaluate Iout values with these
constraints.
iii. Using the principle of superposition, find the Iout of the following circuit using the
results from part ii.
iv. In the figure below, If R1= 9.8K, R2=9.9K, R3=10.3K, R4=10.1K, what should be the
trimming resistors setting (Rt1, Rt2) to obtain maximum output resistance for this Howland
Current Source. Given Rt=5K Ohm
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V. Consider a diff amp with the following modifications
Find an expression for Vout. Comment on how it changes with Vref.
A resistance R is now connected between output terminals; comment on the current
through This resistance R and Vref when Vin is kept constant, and Vref is varied.
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