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ADC Guide, Part 14: Impedance Matching
4/1/2013

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Figure 4
Transformer based impedance matching: (A) RF/IF applications; (B) Baseband applications
Transformer based impedance matching: (A) RF/IF applications; (B) Baseband applications

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steve.taranovich
steve.taranovich
5/14/2019 5:19:27 PM
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Re: How to match if the signal is not monotone?
@raff5184---I am asking the authors to respond

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raff5184
raff5184
5/14/2019 3:54:03 PM
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Newbie
How to match if the signal is not monotone?
Hi, I'm not sure if this thread is stll active. Anyways, how do you choose the inductance L  for the matching if the input signal is not monotone but has a more or less wide spectrum? What frequency should you consider?

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jacksonman
jacksonman
2/2/2018 4:47:27 PM
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Re: Filter before Transformer
Steve....Thank you for your reply and useful refereneces.

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steve.taranovich
steve.taranovich
2/1/2018 3:11:52 PM
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Re: Filter before Transformer
@jacksonman---If you move the anti-alias filter before the transformer---be sure to calculate the reflected transformer impedance that will be seen by the ADC internal front-end. You will need to take care that you have the proper impedance that the internal ADC front end will need to see for optimum bandwidth, plus if the front end is not properly designed to match the interna; ADC input---this can lead to less bandwidth, degraded amplitude, phase imbalance, and sometimes degraded pass-band ripple.

I suggest reviewing the following app notes:

http://www.analog.com/media/en/training-seminars/tutorials/MT-228.pdf

http://www.ti.com/lit/an/slaa416a/slaa416a.pdf 

Check the ADC to see if it has an input buffer as well.

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jacksonman
jacksonman
2/1/2018 1:13:21 PM
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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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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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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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amrutah
amrutah
4/4/2013 9:09:05 PM
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Master
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
4/4/2013 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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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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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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