Re: OP-Amp Configuration

M.Joshi (M.Joshi.28nhkb@xxxxxxxxxxxxx) writes:
Hi,

I was recently in a job interview and was asked to describe an OP-Amp
circuit.

The OP-Amp configuration consisted of negative feedback with a resistor
and capacitor connected in series to ground from the inverting input.

I haven't seen this configuration before and I was asked the purpose of
the capacitor?

What purpose does any capacitor have? To pass AC and not let DC through.
SO when it's used as a coupling capacitor, it lets the AC signal pass
between stages, but blocks the DC from the first stage from getting into
the second stage where it would upset bias. When used as a bypass capacitor,
it in effect shorts the AC signals to ground, without shorting out
the DC voltage.

Of course, a capacitor's ability to pass AC varies with frequency and
capacitance. A small value capacitor won't do well at passing low
frequencies, while a high value capacitor will.

Now given that information, that should have been covered in the books,
why do you think the capacitor is there? Think about why it might
be different from having the resistor going directly to ground.

Michael

.

Relevant Pages

  • Re: LM386 output RC purpose
    ... GND GND ... I've been trying to ascertain exactly what the purpose of this RC ... my calculations indicate that for a Zobel the capacitor value ... Enjoy fashional Electronics with lowest wholesale price? ...
    (sci.electronics.basics)
  • Re: Starting capacitor sizing
    ... capacitor, along with the start winding provides a phase shift to act "kind of" like a 3 phase motor - so you can get the rotating magnetic field rather than just a 180 deg back/forth magnetic field which will just make the motor buzz - ... increase torque during startup, so a manufacturer could utilize a more common or cheaper capacitor if the OEM is specific about the motor application. ... There are a lot of split-phase induction motors that aren't built with a starting capacitor, and they work fine in applications where there is none, or a very low load at startup. ... When I've used general purpose utility motors for applications where the starting load torque was more significant than say, a fan application for example, I've added a starting capacitor to increase the starting torque. ...
    (rec.crafts.metalworking)
  • Re: Tech: I am working on a Data east CPU and I need to replace a ceramic Capacitor
    ... this purpose. ... Edward Cheung CARGPB26 ... 50V 10% PC-Mount Capacitor from Radio shack? ...
    (rec.games.pinball)
  • Re: Question about scope ac-dc diagram
    ... of capacitor do I need to use? ... What purpose do you intend it to serve? ...
    (sci.electronics.basics)
  • Re: Cap. Discharge Res.
    ... I am referring to the capacitor across the ... I am assuming that either the appliance has a faulty resistor connected ... Any cap that is placed across the mains in a piece of equipment, ... should not in theory require any resistor to discharge it, ...
    (sci.electronics.repair)