Work in pairs. Both people in the pair must complete the graph, measurements and calculation.

Your task is to build a MOSFET voltage amplifier and measure its voltage gain.

 

1. Build this circuit.
   
   Get it checked before switching on.
   
   Complete all your measurements, plot the graph and complete all the tasks below before dismantling the circuit again.
   
   
   Here is a possible layout.
   
   
   
2. Measure the gate and drain voltages over a range of values. Record your measurements in a table like this one.
   
   

   Gate Voltage / V	Drain Voltage / V
   0	12
   12	0.02

   
    
3. Plot a graph of your measurements. Your graph will look a little like the one below but MOSFETS are not identical.
   
   
    
4. Mark up your graph as shown above so you can measure how much the input and output voltages change.
    
5. Now calculate the voltage gain of your circuit.
   
   Gain = V_out / V_in
   
   where V_out is the change in output voltage and V_in is the change in the input voltage.
    
6. Why should you NOT include the curved areas of you graph in the voltage change measurements?
    
7. Record your actual layout on a grid.
    

Optional brain stretching challenge tasks.

 

1. You may have found the potentiometer hard to adjust. See if you can design a modified circuit to make the task much easier. Check with your teacher and if approved, build and test your modified circuit.
    
2. What happens to the voltage gain if you replace the 1kΩ drain resistor with 2.2kΩ
    
3. If you complete all these tasks and your teacher agrees, please work on reviseOmatic for the remainder of the lesson.