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Jonathan Harris

Interleaved ADCs: The Basics

Jonathan Harris
jonharris0
jonharris0
5/30/2013 1:41:43 PM
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Re: Re : Interleaved ADCs: The Basics
Hi Dirceu, you are correct that the mismatches are smaller when two or more ADCs share the same package, but unfortunately they are not eliminated entirely....

Great comments and questions to all you guys, thanks!

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jonharris0
jonharris0
5/30/2013 1:40:10 PM
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Re: Re : Interleaved ADCs: The Basics
Hi Sunita, these are good questions.  The upper limit is bounded by several factors.  For ease of understanding the most basic limit is the accuracy of your phase created for each of the n clocks used to interleave n converters.  As n goes higher the phase delta between converters becomes smaller and the impact of any error becomes larger.  As Brad alluded too there are many (proprietary) techniques that can be use to account for errors.  Stay tuned for more on interleaved converters and the gotchas to be aware of...

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DirceuRodriguesJr
DirceuRodriguesJr
5/30/2013 12:32:41 PM
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Re: Re : Interleaved ADCs: The Basics
  I think that problems such as error and gain matching would be minimized when placing  two or more ADCs into same die. I do not know if ADI Blackfin or SHARC feature  interleaved ADCs internally. Some DSCs (Digital Signal Controllers) have multiple ADC / Sample & Hold in MSa/s range. The first idea that comes to mind is to use them to acquire different signals simultaneously - for example, in order to calculate the Power is necessary to measure the Current and Voltage with no delay between.  Conversely, we can join two such independent converters to create an interleaved converter; so that a single signal would be sampled at a higher rate with an appropriate software. Ex., most ADCs in microcontrollers can be triggered directly by a timer that, ultimately, is the generation of those 2*pi*(n-1)/m phase shifts.

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SunitaT0
SunitaT0
5/30/2013 9:15:18 AM
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Re : Interleaved ADCs: The Basics
ADC by itself have issues like DC offset, quantization error. Along with these issues, interleaved ADC's gain and phase needs to be matched. Is it possible to match the behaviour of interleaved ADC's using feedback system ? Can we use digital assisted analog where digital processor analyse the data from interleaved ADC's and provide the feedback.

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SunitaT0
SunitaT0
5/30/2013 9:15:16 AM
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Re : Interleaved ADCs: The Basics
@Jonathan, thanks for the basics of interleaved ADC. Sample rate is increased by the factor of number of ADC, but what are the parameters limiting ADC count for interleaving?

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Brad Albing
Brad Albing
5/29/2013 11:11:21 PM
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Re: Oscilloscopes
As Jonathan noted, there are other details to deal with. He will probably discuss the importance of getting the interleaving timing just right so that the conversion is accurate. Timing skew and jitter are your enemies here. And there are propriatary (in fact, highly propriatary) techniques that different companies promote to address this issue.

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jonharris0
jonharris0
5/29/2013 1:06:29 PM
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Re: Oscilloscopes
Hi Derek, that is correct.  In order to get larger bandwidths for measurement equipment such as oscilloscopes ADCs can be interleaved together.  There are things to watch out for though...(look for future blog posts to find out more).

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DEREK.KOONCE
DEREK.KOONCE
5/29/2013 11:55:39 AM
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Master
Oscilloscopes
Is this not how most digital oscilloscopes operate? It would make intuitive sense that if there is a limit on the speed of the ADC, interleaving multiple ADCs would increase the effective sampling? Thus, it comes down to how fast one can pull data from the multitude of ADCs to process, and to store / display the waveform - the digital side of the system.

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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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