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Simulators >> Circuit Simulators >> Zero crossing points of a differential ampr
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Message started by Vinit on Apr 22^nd, 2004, 2:42pm

Title: Zero crossing points of a differential ampr
Post by Vinit on Apr 22^nd, 2004, 2:42pm

Hello.
I have simulaion results of a differential folding amplifier for an A/D converter.

I want to find out the zero crossings of the output waveforms. I found some article online, which found the zero crossing on the time scale using the calculator feature cross. I tried it and it doesnot work for me.

Any suggestions on how can I get the zero crossings or basically plot the difference between 2 outputs of a differential amplifier.

Thanks in advance !

Title: Re: Zero crossing points of a differential ampr
Post by Andrew Beckett on Apr 22^nd, 2004, 3:44pm

How about subtracting one signal from the other in the calculator, and then using the cross function - you didn't give any clues as to what you'd actually done...

It ought to work, so I can only imagine you did something wrong. If you explain what you tried, that will help...

Andrew.

Title: Re: Zero crossing points of a differential ampr
Post by Vinit Dhulla on Apr 23^rd, 2004, 9:51am

Andrew,
Thankyou very much for the reply. Actually, what I did was, select the wave button on the calculator and then select one of the waveform on my waveform window. Then I clicked on the cross button and then buffer output or something.

I am using this for the first time and just followed the procedure,trying to see if something happened.But,I feel what you said is right, subtract the signal first.

Can u just give me a brief idea on how to subtract signals and then plot zero cross or is there any documentation available that I can refer to.

Thankyou once again.

Title: Re: Zero crossing points of a differential ampr
Post by Andrew Beckett on Apr 26^th, 2004, 9:49pm

Vinit,

If you have the two waveforms displayed in the waveform tool, hit wave, and then click on one waveform, then the other, and then hit the "-" button in the calculator.

Or use VT button and click on both nodes in the schematic,
then -. It's a reverse polish notation calculator, and so you enter the operands first and then the operator last.

Having done that (it will show as waveform1-waveform2),
you can then use cross as usual.

I suggest you read the documentation on the calculator (use the Help menu in the calculator to locate it easily).

Regards,

Andrew.

Title: Re: Zero crossing points of a differential ampr
Post by Vinit Dhulla on Apr 28^th, 2004, 1:41pm

Thanks Andrew,
Your suggestion was very helpful, I was able to do it.

Regards,
Vinit.

Title: Re: Zero crossing points of a differential ampr
Post by Vinit on Apr 28^th, 2004, 1:56pm

Hello ,
I can get the zero crossing for 1 pair of differential amplifier easily. But, I have 90 such zero crossings. Is there a shortcut to get all the zero crossings together or you have to repeat the same process 90 times.

Thankyou,
Vinit.

Title: Re: Zero crossing points of a differential ampr
Post by Andrew Beckett on Apr 28^th, 2004, 10:09pm

Vinit,

Sounds like a good reason to write an OCEAN script to do this. You can then write some code to loop over the differential pairs and do the same computation on each, and print out the results.

Look in the OCEAN Reference Manual in cdsdoc (I think it is under the Analog Design Environment, or something like that, in cdsdoc - I'm writing this from memory).

Regards,

Andrew.

Title: Re: Zero crossing points of a differential ampr
Post by Frank Wiedmann on Apr 29^th, 2004, 12:06am

If you want to find all the zero crossings of a single expression, you can specify 0 as the edge number in the cross function of the calculator (this is documented in the Waveform Calculator User Guide). You will have use the print button of the calculator in this case.

Title: Re: Zero crossing points of a differential ampr
Post by Vinit on Apr 29^th, 2004, 3:36pm

Thankyou guys,
I really appreciate your replies. I think I am not able to make it clear what I want to do. Let me give it a try.

Actually, I am trying to simulate 18 Folding amplifiers(folding rate = 5) together in some fashion. Each folding amplifier output generates 5 zero crossings and hence I have 90 zero crossings.

Initially, I had problems of getting this zero crossing point on the Y-axis, which problem is now solved.

Now, I am trying to study the variation in these zero crossings if I vary some other parameter. Hence I wanted to know a few things:

-- If I can get the value(x-axis) of these 90 zero crossings(ideal) so that I can compare them with the zero crossings after I introduce some mismatch. As you understand, it would be too difficult to first generate the zero crossing for each folding amplifier, note down the 90 values,then generate zero crossings with mismatch and measure each value and compare with the ideal value.

--So is it possible to automatically measure these values and print to file, so that I can compare them easily.

I really thankyou for your help.

Regards,
Vinit.

Title: Re: Zero crossing points of a differential ampr
Post by Andrew Beckett on May 3^rd, 2004, 2:53pm

Vinit,

As I said before, OCEAN is the way to do this. You could
completely automate this using OCEAN.

Regards,

Andrew.