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Number2Pencil
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Homework Statement
Design an op-amp that uses a variable 50k ohm resistor. when this variable resistor is at one extreme, the gain is 13, and at the other extreme, the gain is 3. you may use up to 2 op-amps, and up to 7 resistors (including the variable resistor)
The Attempt at a Solution
here is the circuit i came up with:
I made it so all I would have to find is Rf to satisfy the design.
here is how I solved for Rf
first extreme:
[tex] (1 + \frac{R_f}{60k-ohms}) = 13 [/tex]
next extreme:
[tex](1 + \frac{R_f}{110k-ohms}) = 3 [/tex]
combine the two equations:
[tex]11 + \frac{R_f}{110k-ohms} = 1 + \frac{R_f}{60k-ohms}[/tex]
[tex] 10 = R_f (\frac{1}{60k-ohms} - \frac{1}{110k-ohms})[/tex]
[tex] R_f = 1.32M-ohms[/tex]
this answer gives a gain of 13 on one extreme of the variable resistor and 23 on the other. whoops. any help?
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