Final Project - EE 420L 

Authored by Your Name, Cody McDonald

Today's date: 5/8/19

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

 

 

Part 3: Breadboard Implementation and Testing

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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