ADC12J4000 multiple-device synchronization

Florian Stercq

Other Parts Discussed in Thread: ADC12J4000

Hi,

We are trying to synchronize multiple ADC12J4000 on a same board, using a common sampling clock and a LMK048 for the sysref management. We have no problem being sample-accurate.

However we are surprised about the phase difference we obtain between each channel. With a clock frequency @4GHz, we measure a maximum deviation of about 40 degrees between 2 channels (about 27ps).

Our layout is fully constrained. Measuring signal and clock at ADC inputs with a scope shows a maximum deviation of about 5 degrees between 2 channels.

We therefore consider that the phase difference is due to a variation of aperture delay between ADCs. Do you agree with this assumption? Can you tell us if the variation of aperture delay between ADC12J4000 can be so significant?

Kind regards

Florian Stercq

over 8 years ago

0 Jim Brinkhurst1 over 8 years ago

TI__Mastermind 43910 points

Hi Florian

To minimize differences in Aperture Delay time from chip to chip, the designers try to minimize the amount of circuitry between the clock input and the actual Track and Hold control.

In spite of these efforts some active circuitry must be used, and due to variations in manufacturing there will be some differences in Aperture Delay between any two devices. The skew you are seeing is within expectations for this device family. Please see this earlier post where the expected variations are listed:

If smaller skew is required in your system then a skew adjust mechanism must be added in the ADC clock path, and a tuning method must be used to find the best skew adjustment to align the sampling events.

Best regards,

Jim B

0 Florian Stercq over 8 years ago in reply to Jim Brinkhurst1

Prodigy 170 points

Hi Jim,

Thanks a lot for this quick answer.

Best regards

Florian

0 Florian Stercq over 8 years ago in reply to Jim Brinkhurst1

Prodigy 170 points

Hi Jim,

We wonder if there is any mechanism inside the ADC we could use to adjust the clock delay. That could interest us even if no support is provided on it.

Best regards,

Florian

0 Jim Brinkhurst1 over 8 years ago in reply to Florian Stercq

TI__Mastermind 43910 points

Hi Florian

Unfortunately this device does not have any internal mechanisms to adjust the clock delay, or sample timing.

Regards,

Jim B

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ADC12J4000 multiple-device synchronization