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 unstable.
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.