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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