the op amp can process digital signals?

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EDA_hg81

Joined: 25 Nov 2005
Posts: 395

29 Oct 2009 15:20 the op amp can process digital signals?

I am wondering if the op amp can process digital signals.

If it can do this processing which considerations I have to take care?

Thanks

AdrianN

Joined: 28 Jun 2009
Posts: 20
Helped: 10
Location: California

29 Oct 2009 17:29 the op amp can process digital signals?

It depends on what you consider processing. The Op Amp will consider the digital signal as analog one. If the Op Amp receives a 0...5V signal for example, it can amplify it, attenuate it, add another signal to it, subtract another signal, filter it, etc, whatever an Op Amp can do to a signal.

If, by processing, you mean Digital Signal Processing, as in data processing, no, it cannot do it.

EDA_hg81

Joined: 25 Nov 2005
Posts: 395

29 Oct 2009 18:03 Re: the op amp can process digital signals?

I only consider use op amp to process digital clock signal.

I am wondering if the processed digital clocks still can drive digital chip, such as the output current of opamp can meet the input current requirements of digital chip?

Thank you again.

dick_freebird

Joined: 04 Mar 2008
Posts: 313
Helped: 46
Location: USA

29 Oct 2009 18:24 the op amp can process digital signals?

I think that most op amps have slew rate limitations that
a digital input buffer may not like, or be able to chatter
against (slow dV/dt, time in linear window and ambient
/ self-switching noise).

You would have to criticize the candidate op amp in this
respect as well as its supply and drive attributes.

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EDA_hg81

Joined: 25 Nov 2005
Posts: 395

29 Oct 2009 18:58 Re: the op amp can process digital signals?

I am using a op amp from Ti such as opa4658, the slew rate of it is 1700v/us.this

but this opa4658 can soure current typically at 120mA, can I put a inveter such as 74HCT04 between the output opa4658 and digital input buffer?

If the slew rate is lower than digital part, the digital chip is easy to latch up.

But if my slew rate is higher than slew rate of digital input buffer, is it ok?

Thanks for answers.

AdrianN

Joined: 28 Jun 2009
Posts: 20
Helped: 10
Location: California

29 Oct 2009 20:51 the op amp can process digital signals?

OPA4658 output is bipolar, while the input of 74HCT04 is unipolar. So, make sure you limit the op amp output voltage to the positive region.

Even so, you cannot just power the opamp between 0 and 5V, because the opa4658 output low level is about 2.3V from rail so the HCT04 will not be able to "see" a VOL level in its input. You will need to drop the op amp negative power supply input below ground by 2V to be able to drive the input of HCT04.

Another solution is to use a different op amp like a rail to rail one, that can drive its output close to the rails. Make sure it has a good slew rate as previously stated.

FvM

Joined: 22 Jan 2008
Posts: 5162
Helped: 767
Location: Bochum, Germany

29 Oct 2009 21:29 Re: the op amp can process digital signals?

I can imagine many ways to interface an OP output to a digital circuit, first of all, it should serve a purpose.
But I don't hear it from your considerations yet. What's the use of it?

Some points, e.g. regarding relation of slew-rate, output current and latch-up sound simply wrong.