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https://designers-guide.org/forum/YaBB.pl Measurements >> RF Measurements >> 2 MHz Instrumentation Amp https://designers-guide.org/forum/YaBB.pl?num=1212137894 Message started by aaron_do on May 30th, 2008, 1:58am |
Title: 2 MHz Instrumentation Amp Post by aaron_do on May 30th, 2008, 1:58am Hi all, I need some kind of buffer with SMA inputs with an input capacitance of no more than 2 pF to work up to 10 MHz. Does such a buffer exist, or do i need to design on-chip buffers? thanks, Aaron |
Title: Re: 2 MHz Instrumentation Amp Post by pancho_hideboo on May 30th, 2008, 6:51am aaron_do wrote on May 30th, 2008, 1:58am:
As far as you connect an amplifier to DUT via 50ohm coaxial cable, a capacitance loaded to DUT is far larger than 2pF even though an input capacitance of amplifier is 2pF. Or you expect 50ohm impedance of amplifier ? What signal do you want to observe ? Oscilloscope ? Spectrum Analyzer ? aaron_do wrote on May 30th, 2008, 1:58am:
I use active high impedance probe both for Oscilloscope and Spectrum Analyzer. There are many excellent probes available. Or I use OP Amp of ADI. Then connect DUT to OP Amp with very short line on board. I often use following. http://www.analog.com/UploadedFiles/Data_Sheets/AD8138.pdf Maybe AD8138 is too over spec for your purpose. You can find reasonable one in ADI's products. But maybe on-chip buffer is most cheap. |
Title: Re: 2 MHz Instrumentation Amp Post by aaron_do on Jun 1st, 2008, 8:19pm Hi, thanks for the reply. BTW, do you know what kind of input-referred noise I could expect from an active high impedance probe? thanks, Aaron |
Title: Re: 2 MHz Instrumentation Amp Post by pancho_hideboo on Jun 1st, 2008, 10:04pm aaron_do wrote on Jun 1st, 2008, 8:19pm:
You might be able to get such informations from data sheets of active probe. By why don't you measure DUT ground with probe. That is noise floor. |
Title: Re: 2 MHz Instrumentation Amp Post by aaron_do on Jun 1st, 2008, 11:15pm Oh i don't actually have the probe at the moment. My university bought a very high-end (up to 20+ GHz) one from picoprobe but there were compatibility issues. So i was thinking of suggesting to my supervisor to try and get a lower-end active probe for use up to only a few hundred MHz. If i have to design a buffer just because the active probe's noise floor is too high then i would be a little more reluctant... I have a data sheet for the high end probe but it says nothing about noise... thanks anyway, Aaron |
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