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Jonathan Harris

ADC Noise: The Clock Input & Phase Noise (Jitter), Part 2

Jonathan Harris
etnapowers
etnapowers
3/11/2014 7:18:48 AM
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Re: measurement accuracy
@jonharris0: yes, it does make sense to me, the ADC determines the perfomance of the system not only for data sampling but also for data conditioning, the data in binary format are stored in the computer memory, that has to be capable of storing a big quantity of data, depending on the resolution of the ADC.

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jonharris0
jonharris0
3/10/2014 7:47:12 AM
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Re: measurement accuracy
Great question.  The data conversion is done inside the ADC so the performance is determined inside the ADC.  The software on the PC is merely processing the digital data that has already been converted by the ADC.  Does this make sense?

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etnapowers
etnapowers
3/10/2014 3:50:01 AM
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Newbie
Re: measurement accuracy
@jonharris0: I'm looking forward for a blog on this. you're welcome, thank you for the details you provided, I guess that the data are collected in the memory of the PC by a conditioning system to convert the data from analog to digital format.

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jonharris0
jonharris0
3/5/2014 4:35:53 PM
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Re: measurement accuracy
This is a good point to look at.  Actually, the instrumentation that makes the most difference in terms of testing the ADC in this manner is the analog input signal generator for the ADC and the reference input signal generator for the clocking IC.  The measurements are done on a PC using Visual Analog software.  Perhaps a good topic for a blog would be an overview of the test setup to show how this data was collected on the AD9643 and AD9523. Thanks for the question!

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etnapowers
etnapowers
3/5/2014 11:11:23 AM
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Newbie
measurement accuracy
The correlation between simulated and measured results is good, provided that there is a good accuracy of the testing instrumentation utilized in laboratory to test the noise.

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jonharris0
jonharris0
3/3/2014 9:04:51 AM
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Re: Jitter equation
Hi DaeJ, thanks for your comments!  Great question! The equations can be applied to any ADC and clocking source, not just the AD9643 and AD9523.  These two devices are just given for an example to show that the math will predict the overall SNR. 

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DaeJ
DaeJ
3/2/2014 3:25:09 PM
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Master
Jitter equation
It is validated that the predicted data was almost the same as that of measurement data. These equations are based on AD9643 and AD9523 with clock input to calculate jitter noise. I wonder whether these equations could be applied to other components made by different manufacture.

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More Blogs from Jonathan Harris
Previously in this blog series we looked at using a DC/DC converter (switching regulator) in combination with an LDO to drive the power supply inputs to an ADC. What we found was that using the DC/DC converter to step down the input voltage for the LDO was a much more efficient way to drive the power supply inputs to an ADC.
We look at using a DC/DC converter along with an LDO to drive the ADC power supply inputs.
I thought it would be good to continue looking at the example I gave in my last blog where we looked using fewer LDOs and combining power supply rails on an ADC while maintaining isolation with ferrite beads.
There are some disadvantages when driving low input supply voltages, where multiple LDOs may be required.
Keeping the power supply inputs on separate domains can minimize crosstalk and make it much harder for noise to interfere with ADC performance.
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