Sample input and output impedance problem:
Find the input impedance seen by the voltage source, and find the output impedance.
Input impedance:
Since the question asks to find the impedance seen by the source, we would take the source out,
and find the impedance between those terminals (i.e. the 2 terminals where the source used to be).
Then the technique would be to apply a source to those terminals (say Vin), and find the current
through the source (say Iin), then the input impedance would be Vin/Iin.
If we apply a known Vin, the problem is basically to find Iin. In this case, that would be the
current through the lefthand 5 Ohm resistor. In order to find that current, we would “solve” the
op amp problem with our standard techniques, and find the voltage at the + input terminal in
order to find the required resistor current.
In this particular problem, since there are no independent sources in the circuit, we could actually
apply any voltage source (even the 5V as shown), and get the same answer, i.e. the answer
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This note was uploaded on 04/30/2010 for the course BENG 186B taught by Professor Peterchen during the Winter '08 term at UCSD.
 Winter '08
 PeterChen

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