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ADS4122: ADS high speed ADCs clocking : combine low jitter and high temperature stability

Part Number: ADS4122
Other Parts Discussed in Thread: ADS4128, ,

Hello,

In one of our designs we have several ADS4122 & ADS4128.

Right now we use very low jitter LVDS oscillators (Silabs 560 series with +-20ppm stability) to drive them which allow us to meet the ADC datasheet stated performance.

However our client would like to have more stable oscillators (below 1ppm).

In the past we've used this kind of clipped sine wave oscillators, but I worry the cmos circuits would add a lot of phase noise.

Do you have experienced such circuits ?

If so, will this degrade the performance of your ADCs ?

Many thanks,

  • Victor,

    At low sampling frequencies, jitter does not effect performance as much. What kind of numbers are they getting now? Are they within the data sheet specs? What is the actual part number of the oscillator?  What is the analog input frequency they plan on using? Is the clock input amplitude within data sheet specifications?

    Since they are using single-ended clocking mode, make sure the negative clock input is connected per Figure 47 of the data sheet. 

    We have never tried clocking this part this way. We have tried with clipping diodes with some success.

    Regards,

    Jim

  • Hello Jim,

    The ADS4122 runs @ 40MSPS, whereas the ADS4128 runs @ 200MSps. The obtained numbers are within TI's datasheet (I've measured ENOB 11.0 bits for the ADS4128 in their application for example).

    Input frequencies can be as high as 1/3 of the sampling rate. The current oscillator's jitter is max. 160fs which is very good. These oscillators are used in LVDS mode.

    But the issue is that I can't find any oscillator with both low drift and low jitter that can directly drive these ADCs.

    Can you suggest an oscillator manufacturer or a particular clock circuit that could help me to reach this goal ?

    Thanks,

    Victor

  • Victor,

    The ADS4122EVM uses a CDCE72020 to clock the ADC. Other ADC boards have used oscillators from Crystek, model #CVHD-950.

    The TI high speed clocking group has the LMK61xx oscillator that may be an option. Check with this group to see if they have other options available.

    Regards,

    Jim