phys 351 lab 8

phys 351 lab 8 - Lab 8: Transistor Based Amplifiers Section...

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Lab 8: Transistor Based Amplifiers Section A-1: FET Operating parameters In section A-1, a circuit was built in order to find the relationship between drain source current and drain source voltage dependence for an N channel silicon FET. First, V GS was set to 0 and R was adjusted until V DS was about 5V. The value of R that was used was 1.5kOhms. This was done to find the current Id. Id was then measured as a function of V DS for a range of V GS values from -5V to 0V. The gate voltage was decreased from zero in order to find g m . g m was found to be .00053 using the equation GS D m dV dI g / = , which is the ratio of change in source current to the change in gate voltage. Next a graph of sqrt(I d ) vs V GS . The following was observed. Sqrt(Current) vs. Gate Source Voltage y = 0.0365x + 0.0849 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 -6 -5 -4 -3 -2 -1 0 Gate Source Voltage Sqrt(Current) Amps Series1 Series2 Linear (Series2) Figure 1.1, Graph of sqrt(Id) verse Gate source voltage
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Figure 1.2 Circuit used in A-1 The graph was very useful in that we could solve for two different constants from the following equation. 2 ) ( T GS DS V V K I + = The constants that we desired to find out were K and V T . First K was solved for, using the relation that the square root of K is the slope of the line. This was found to be .191. Knowing this, V T could next be found knowing that square root K times V T is the Y intercept. Using this, we solved and obtained a value of 2.326 for V T . (Note, after doing this lab, some labs were told to do this part in EWB, however we were told to do it in Lab). Looking back at the difference between the lab and EWB is that the line appears to be linear instead of flattening out at 0
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phys 351 lab 8 - Lab 8: Transistor Based Amplifiers Section...

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