The Designer's Guide Community Forum

The Designer's Guide Community Forum
https://designers-guide.org/forum/YaBB.pl
Measurements >> Other Measurements >> how to measure bandgap?
https://designers-guide.org/forum/YaBB.pl?num=1189658184

Message started by lightgo on Sep 12^th, 2007, 9:36pm

Title: how to measure bandgap?
Post by lightgo on Sep 12^th, 2007, 9:36pm

i want to measure the psr,intergrated noise from 100Hz to 100KHz,and temperature coefficient
who can give me some help

Title: Re: how to measure bandgap?
Post by Faisal on Sep 13^th, 2007, 8:13am

I have an even more basic question.. I want to measure the bandgap voltage and its variation w.r.t to the frequency.

I intend to put a probe/test pad (opening in the passivation layer) to measure the bandgap voltage. The equipment in our lab has a dc - probe needle and triax cable (approx 100pf/m) .. the problem is that bandgap is too sensitive to load capacitance.

Do I need to use buffers.. or better cables.. what are the possibilites?

Kind Regards,
Fas

Title: Re: how to measure bandgap?
Post by ywguo on Sep 14^th, 2007, 8:16am

Hi Faisal,

Where do you probe the bandgap voltage? Would you please show a schematic and which node do you probe?

I don't understand the reason why the bandgap voltage is sensitive to the load capacitance.

Thanks
Yawei

Title: Re: how to measure bandgap?
Post by Faisal on Sep 21^st, 2007, 9:52am

Hi,

I wanted to probe the bandgap at its output. The bandgap output is sensitive to capacitance, because the bandgap core consists of a two stage error amplifier, to equalize node voltages. This is quite a standard design, discussed in text books.

Now i dont intend to observe the output of the bandgap directly, but indirectly after a buffer.

Title: Re: how to measure bandgap?
Post by thechopper on Feb 28^th, 2008, 4:36pm

Faisal wrote on Sep 13^th, 2007, 8:13am:

Do I need to use buffers.. or better cables.. what are the possibilites?

Kind Regards,
Fas

Hi Faisal,

You could try out active probes (which usually have much smaller capacitances than the passive ones) and shorten the cables as much as possible.
Buffers are another alternative but might offset to your measurement.

Hi ligthgo,

One option to measure noise is to record at least 100 sweeps of the bandgap voltage signal, 0.01s long each, from the scope. This way you are letting the noise content of 100Hz an above to take effect on the signal, and at the same time taking fairly enough number of samples. You could then capture the datapoints from the scope and process it with matlab, by using one of the PSD estimators it provides. After such calculation you will be able to see the profile of the noise signal and its total power by simply integrating it.

Hope this helps
Tosei