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Powering High Performance Op Amps and ADC/DACs


Adelec Bakkal

Jan 1, 1970
Hello to everybody,

I am designing a high speed analog I/O board. I am worrying about
several points concerning the power supply, mainly :

(1) The effect of the its impedance at high frequencies on the
distortion and noise level
(2) The effect of this impedance mismatch between the positive and the
negative rail.

To be more specific and have better answers and discussions, here are
more details:
ADCs : 14 bits, somewhere from 40 MSPS to 125 MSPS
DACs: 14 bits, 200 MSPS to 300 MSPS (Current output)
The analog signal paths are to be fully differential.
I am looking into TI/BB portfolio, ADS and DAC families. The fully
differential amplifiers have been choosen based converters' data sheet
recommendations : the THS family. The recommended power rails for the
THS4509 + ADS5500 was +4V / -1V for optimum operation.

I am worried about the feedthrough and crosstalk between the different
converters by the means of the power supply, because of the high
bandwidth opamp, and the low PSRR ADCs/DACs. I would like some guidings
on designing a separate linear power supply for each converter and its
opamp, preferably based on standard linear voltage regulators. I am
considering the LM317 / LM337 family (from TI and National), keep your
comments on designing with those parts coming, especially the type of
the output capacitors, and if ever, any wise filtering topologies. I
would like also to hear about the things that might get regulators

I don't know if it's OK to use those LM317 / LM337 for such an
application, but I think that a careful desgin should do better than
expensive parts.

Finally, does anybody know if having symetrical impedance on both
positive and negative rails have any beneficial effect on the
distortion level of high speed fully differential amplifiers?

Please feel free to drop me any tip / advice. I will manage to try them
on a first prototype.