Final Project - EE 420L
e-mail:
mcdonc4@unlv.nevada.edu
This lab
will include:
Part 1:
Project description
Part 2:
Design Selection
Part 3: Breadboard
Implementation and Testing
Part 1: Project Description
Design a voltage amplifier with a gain of 10 using
either the ZVN3306A or ZVP3306A (or both) MOSFETs and as
many resistors and capacitors as you need. You should try to get as fast a design as
possible driving a 1k load, with an input resistance greater than 50k, with as
large of output swing as possible. AC coupling input and output is okay as long as your design can pass a 100 Hz input signal. Your
report, in html, should detail your design considerations, and measured
results showing the amplifier's performance. Your
design can draw no more, under quiescent conditions (no input signal), than 1
mA from a +9 V supply voltage.
Part 2: Design Selection
There
were quite a few design specifications we had to take into
account for the design of this amplifier. The design needed to be as fast
as possible, be able to push a 1K load, and be able to draw current less than
1mA from a 9V supply voltage. The topology that seemed to be able to already
handle some of these specifications was the push pull amplifier. It would inherently
already have a very high input resistance and be able to provide a high enough
gain. The only downside would be the current draw, which would be very high. We
would be able to remedy this by adding a tail resistor to dissipate some
current.
Our
original design utilized the benefits of the push-pull circuit along with using
a source-follower amplifier as an input buffer. The source follower also had
the added benefit of being able to control the input resistance. Here was our
first design:
Unfortunately,
when implementing this design on the breadboard we were unable to obtain an
adequate gain. We later had to simplify the design to just the push-pull amplifier.
This was our final design:
Current Draw Analysis
Running the operation of our design we can see that we have a
device current draw less than 1mA under quiescent conditions. More specifically
our current draw was 0.889mA.
Gain Analysis
Calculating the gain of our topology:
Our spice error log indicates a Gmn of 148uA/v and a Gmp of
162uA/v
Substituting our values in we get the following
Our requirement for this design was to produce a gain of at
least 10 given an AC input past 100Hz. Given a 1V input we are obtaining a gain
of roughly 11 through 1MHz, which satisfies our gain requirement for this
design.
Input Resistance
Calculating the input resistance of our topology:
Substituting in our values we get:
We can see that our simulation indicates an input resistance
that is well above the 50k requirement and that our measurements match our hand
calculations.
Circuit
Speed
We will
be observing roll-off frequency to determine how quickly our circuit can
operate. If the roll-off frequency is rather high, it will mean that our
circuit is able to operate quickly.
The
roll-off frequency was observed to be approximately 530kHz
Upon
breadboarding we had to adjust our design slightly to use these values in our
circuit:
Resistor
R1,R2,R4, and R5 needed to be decreased substantially
before we started seeing a gain like what we had first calculated along with several
of the other resistors.
Gain:
Our
circuit was able to generate the calculated gain of approximately 11.
Here is a
view of our apparatus:
Output swing:
Our
output swing provided a 3V swing upwards and a 2V swing downward for total
output swing of 5V
Roll-off
Freq:
We determined
the speed of our circuit by observing the roll-off frequency of our circuit. We
can see that our circuit can handle speeds of up to 578kHz as what was observed
in the simulation. The gain of our circuit does not fall off until then.
Input
Resistance:
We will
be measuring the input resistance by placing a resistor out the input the
amplifier and measure the voltage drop across the resistor. This will then give
us the input current. We will then be able to calculate the input resistance by
dividing the input voltage by the input current. We will be using a 180K resistor
to find our input current and our input voltage will be 50mV.
This
value lines up with our simulation of 1.8Meg of input resistance.
Quiescent
current draw:
To
measure our quiescent current draw we used an ammeter connected from VDD(9V source)
Conclusion
Overall, we
were able successfully design a low power voltage amplifier that would produce
a gain of 10 or greater. This design challenge was very interesting in regard to adjusting the parameters of the circuit to be
able to satisfy all of the constraints. The process involved increasing or decreasing
several of the resistors to provide a greater gain and a lower current draw. I
found that it was difficult decreasing the current draw while trying to
maintain the gain. Eventually, we found the correct values of our resistors to
implement this design challenge.
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