A
Frequency Response Laboratory Problem - 2
Willy
Nilly has heard of your work on low pass filters, and he needs your help.
He has heard that you are familiar with this circuit. In a previous
exercise you may have found that this circuit is a low pass filter.
However, Willy has heard that there may be better low pass filters, and
he wants you to investigate two possible circuits that might be better
than this circuit.
Here is the first circuit. It is just two copies of the first low
pass filter "pasted together". The output of the first circuit becomes
the input to the second. BUT, it is more complicated than that because
the second circuit (R2, C2) loads the first circuit
(i.e. it draws current from the first circuit.). That means that
any analysis you did for the first circuit is invalid because you didn't
consider any loading effects!
Here is the second circuit. It is considerably different. It
also has two resistors and two capacitors, but is also has that pesky operational
amplifier.
Now, it is claimed that whatever the first circuit does can also be done
by the second circuit, and that it can do some things that the first circuit
cannot do.
Willy doesn't understand why any of this is true, and he has asked you
to do a little investigation. He needs you to give him the following
information.
l A
formula for the frequency response of
each circuit.
l Experimental
verification of those formulae.
l An
evaluation of both circuits. Can you make
better filters with these circuits? How so?
Is one better than the other?