We definitely need +/- 15V for the low frequency (e.g. trap electrode) amplifiers. Many low noise amplifiers and RF components run off +5V or +/- 5V and have substantial current draws, so if you pull everything from +/- 15V rails you are tripling your power dissipation and you end up with very hot regulators. The DACs and ADCs will be dissipating a fair amount of power already so we want to try to keep the power budget under control. Other than that, I don’t see major reasons why one couldn’t run fewer analog rails. I think we are better off with DC/DC converters on the AMC card making a number of rails, which then have some filtering/regulation on the AMC card and then a final stage of LDO regulation on the FMC daughtercard itself, as close to the amplifiers etc as possible.
Using the alternating grounds a la CERN seems like a suitable solution to me for sending in these additional analog rails. From: Grzegorz Kasprowicz [mailto:kaspr...@gmail.com] Sent: Wednesday, March 30, 2016 3:13 PM To: Slichter, Daniel H. (Fed) <daniel.slich...@nist.gov> Cc: Robert Jördens <r...@m-labs.hk>; Grzegorz Kasprowicz <gkasp...@elka.pw.edu.pl>; Leibrandt, David R. (Fed) <david.leibra...@nist.gov>; Sébastien Bourdeauducq <s...@m-labs.hk>; artiq@lists.m-labs.hk Subject: Re: [ARTIQ] FW: initial specification of the project Well, CERN does it in their FMC carriers. They use HPC routed like LPC and then some of grounds are used as symmetrical analog supplies. In this way if you plug wrong board, it will short the supply but no damage will occur. I assume that low nosie DC/DC converters + LDOs will be installed on the AMC board. Do we need all these voltages, especially +/-5 and +/- 15? Won't single +/- 8 or +/- 15V be sufficient? Greg On 30 March 2016 at 23:08, Slichter, Daniel H. (Fed) <daniel.slich...@nist.gov<mailto:daniel.slich...@nist.gov>> wrote: Actually HPC with LPC IO assignment and 8 x GTP links is popular configuration So you have 34 LVDS pairs and 8 GTP links. If this works for you then I don’t have major objections. The other issue to consider is power rails, since for the analog circuitry we will probably want +/- 5V, +/- 15V as well as +3.3V, +1.8V, +12V. Can we put these through on the FMC without breaking back compatibility? For example, one rail on each of the 4 VADJ pins? I am sure this would not be VITA 57 compliant….and we don’t want switching converters on the FMC daughtercard for space and noise reasons both.
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