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Sachin Gupta & Akshay Phatak

ADC Guide, Part 14: Impedance Matching

Sachin Gupta
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amrutah
amrutah
4/2/2013 11:51:41 AM
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Difficult to handle the inductance
Is using the inductance the only method to match the impedence? The input parasitic capacitance to ground can form a parallel resonant circuit. If the series cap and the parasitic cap are of the same order than the 2 resonant can cause problems...

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amrutah
amrutah
4/2/2013 11:56:30 AM
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Transformer
"For RF or IF applications, transformer-based matching circuits are more popular."

Usage of the transformer wil  help by isolating the input of the ADC from source but it will make the system bulky.  Only from Impedence matching perspective is transformer used or are there any other advantages?

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Vishal Prajapati
Vishal Prajapati
4/3/2013 5:24:57 AM
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Master
Re: Difficult to handle the inductance
Sachin/Akshay, Can you suggest some good books or literature for impedence matching? Can we try to simulate this reflection of signal or impedance matching in the PSPICE or similar software?

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Hughston
Hughston
4/3/2013 11:02:01 AM
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Newbie
Re: Transformer
Transformer coupling is very convenient to use for an ac differential signal in a mixed signal system with multiple grounds. It gives great CMRR between noisy grounds. I think you will be flat enough over your bandwidth with a transformer because because the IF frequency is going to stay within a limited enough range. I am making an assumption with that last sentance.

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Brad Albing
Brad Albing
4/4/2013 10:10:28 AM
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Re: Transformer
And even tho' it's been mentioned before, it bears repeating: Even with a good quality, properly wound transformer, you will lose that good CMRR if you don't pay careful attention to your PC board layout  - parts placement, trace length, matching and co-locating traces, etc.

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Brad Albing
Brad Albing
4/4/2013 1:17:52 PM
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Re: Difficult to handle the inductance
Pick your inductance value carefully with respect to the frequency (or bandwidth of the frequencies) that matter in your system. Also, adding resistance to lower the Q of the resonant circuit can help some.

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amrutah
amrutah
4/4/2013 9:09:05 PM
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Re: Difficult to handle the inductance
Akshay,

   This is one of the topic very difficult to understand and get a intuitive feel for the subject.  Though there are tons of data available on the subject, but it would be helpful if you could point to some good material for impedence matching, understanding Schmitt charts....

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Brad Albing
Brad Albing
4/30/2013 10:31:49 AM
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Re: Difficult to handle the inductance
We'll get some info from the authors. I'll let them know.

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Brad Albing
Brad Albing
4/30/2013 11:29:11 AM
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Re: Transformer
We'll need to get a blog posted regarding PC layout techniques that speaks to this specific issue.

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jacksonman
jacksonman
2/1/2018 1:13:21 PM
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Newbie
Filter before Transformer
Is it possible to put the anti-aliasing filter before the transformer so as to design the filter as single ended only, giving the advantage of having less inductors that might introduce lots of tolerances?

My frequency of operation is 50 MHz and I need to design a 7th order filter.

What would be the benefit of having the filter after the transformer instead of before it?. From noise filtering point of view I donot see any difference!

Thanks,

Karim

 

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Page 1 / 2   >   >>
More Blogs from Sachin Gupta & Akshay Phatak
In the previous part of this series we looked at differential vs. single-ended drive methods for the ADC. This installment of the series looks at ADC input impedance and the effect it has on accuracy.
In previous part of this series we discussed the noise specifications of an ADC. This installment of the series talks about the ADC input configuration.
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