Lab Project - EE 420L: Engineering
Electronics II
James Mellott
mellott@unlv.nevada.edu
05/03/2017
Project - design a transimpedance amplifier (TIA) using either the ZVN3306A or ZVP3306A (or both) MOSFETs and as
many resistors and capacitors as you need with a gain of 30k. You should try to
get as fast a design as possible driving a 10k load with as large of output
swing as possible. AC coupling input and output is okay if your design can pass
a 100 Hz input current. Your report, in html, should detail your design
considerations, and measured results showing the TIA's performance.
Note that this is the same project assigned last year so this year we will have
one more constraint, that is, your design can draw no more, under quiescent
conditions (no input signal), than 0.3 mA from a +9 V supply voltage (quiescent
power consumption is less than 2.7 mW for any power
supply you use).
Design
Considerations:
A
trans-impedance amplifier (TIA) converts a current input to a voltage output.
The design for selected for this project is a simple push-pull amplifier. The
topology used for this project is seen below in figure 1 followed by the
simulation results. The implementation of the push-pull amplifier
requires 2 transistores, the problem is just using two transistors I can not
limit the current flowing in and out of the amplifier. I decided to build
a beta multiplier which will hold my current constant and generate bias
voltages to control current that flows into and out of the amplifier.
Figure 1 TIA Schematic and Simulation results
The
design utilizes a beta multiplier to generate a reference current roughly
57uA. The beta multiplier can be seen on the left side of the schematic.
Using the beta multiplier, I generated bias voltages to control the current
entering and leaving the push-pull amplifier to meet design
specifications. The quiescent power limitations were to be below 2.7mW
power consumption and less than 0.3mA from the power source. Below in figure 2
is the DC quiescent current and power used by the circuit above.
Figure 2 Quiescent Conditions
The
design is just below required quiescent power conditions. While the gain
of the amplifier is roughly 114db and passes 100hz as seen by the simulation
results from figure 1. The push-pull topology is ideal for this project
as it offers high gain with high efficiency.
The
gain of the TIA amplifier is calculated by taking the following: Vout/Iin where I calculated Iin from the voltage drop across R3 divided by R3.
Experimental:
Below
in figure 3 is the experimental results I achieved using the topology form
figure 1.
Figure 3 Experimental Gain
The
gain was calculated by taking the peak to peak voltage across R3 and dividing
it by R3 where R3 in the experiment was 10k. The voltage drop was
calculated using the math function on the O-Scope, denoted by M in figure 3
above.
The
following is the schematic and simulation results for the output swing
experiment. The output is centered at 0 due to the capacitor on the
output.
Figure 4 Output
Swing Simulation
Increasing
the input voltage to 40 mV from 10mV gave the output swing seen in figure 5
below. Increasing the input voltage any more than 40mV clipped my signal
on the low side, meaning I was hitting the lower rails of the amplifier.
The largest output swing I was able to achieve was
roughly 900mV peak to peak.
Figure 5 Output Swing
Conclusion:
The
TIA design has a 425k gain and can drive a 10kΩ load and pass a 100Hz
signal. The design constraints initially proved to be a challenge when
designing the circuit for this project, I knew I needed to limit the current
supplied which is why I used a beta multiplier. From there, with some
help, the push-pull amplifier was chosen as the output stage. With
voltage controlled current sources and sinks I was able to
control the current entering and leaving the amplifier. This topology
offers high gain with low power consumption.
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