# Help

Discussion in 'Homework Help' started by mcconnellr, Feb 22, 2005.

1. ### mcconnellr Thread Starter New Member

Feb 22, 2005
2
0
for a differential operational amplifier, why can't a cosine source be in series with a capacitor on the negative input???? thanks a lot for your help!!

2. ### hgmjr Moderator

Jan 28, 2005
9,030
214
Your question is broadly stated so I may have misinterpreted it a bit. Also without a circuit diagram it is difficult to envision the exact nature of your problem.

Assuming that you're referring to the classical form of a differential configured single stage opamp, the voltage or signal source is floating. By floating, I mean that the source of your signal is not referenced to ground. For example. a magnetic read head is an example of a signal source that has no inherent reference to ground.

The differential configured opamp should behave in a predictable manner when a capacitor is placed in series with its floating source.

If the value of the capacitance is too small it may represent an impedance that is too high at the frequency range of interest to you.

Another problem could arise if the capacitor you are using is of a polarized type. By polarized, I mean a capacitor with a positive terminal and a negative terminal. An example of this type of capacitor would be a Tantalum or Electrolytic capacitor.

Sorry for rambling on. If I didn't answer your question clearly maybe you could elaborate on your circuit. If you could provide a schematic of the circuit in question, I am sure I could provide a more accurate response.

Good Luck.

3. ### mcconnellr Thread Starter New Member

Feb 22, 2005
2
0
sorry for the brief explanation before..
our teacher gave this problem as an extra credit and we are supposed to explain why you can not get an anser for Vo. He gave us the hint that it has something to do with properties of capacitors.It wouldnt let me attach the schematic, but email me at mcconner@uwplatt.edu and i might be able to send it that way. Thanks Again!!