Re: FDC meeting minutes

[John Schaapman <jsch@phys.ualberta.ca>]

Hi Fernando,
  With regard to item # 2.  In addition to eventual " V threshold" 
distribution, consideration should be given to whether the "mode" select 
between analog/disc output from the ASIC will be done external to the 
detector or with a jumper on the preamp board. I guess external control 
would only be necessary/usefull for the anode readout.

John

On Thu, 18 Jan 2007, 
Fernando J. Barbosa wrote:

> Hi Gerard,
> 
> I have attached the preliminary schematic and layout for the preamp card.
> 
> I have not included a pulser in the card - the test/calibration pulse is 
> input via the 25th pair, distributed to all 24 channels on the board via 
> capacitive coupling (trace area overlap) and terminated at the 
> characteristic impedance of the cable. This is standard fare and 
> provides enough flexibility. This requires the pulsing circuit to be 
> located on the fADC-100 which can be controlled via VME.
> 
> Major factors are: the power dissipation on a 24 channel board is 
> already over 1 Watt, heat removal is difficult and space is very 
> limited. There is also the option of putting the pulser circuitry on the 
> translator board as long as there is not much power involved. I must say 
> I don't like this option because of serviceability issues. Putting the 
> pulser circuitry on the card is possible, however, but we need to 
> consider the power supply, power dissipation and size and noise issues.
> 
> The general philosophy is:
> 
> 1. The +3V supply is distributed to the various preamp cards via the 
> translator boards. Each translator board can be fed from the power 
> supply or daisy-chained, depending on space constraints and current. 
> High precision +2.5V regulators are required and installed on each card 
> to service all 24 channels. I outlined why the ASIC supply must be well 
> regulated on a previous email.
> 
> 2. The same power connector may include a threshold voltage input to be 
> distributed to every preamp card. If the card does not have any 
> discriminators (Mitch is interested in incorporating these into the 
> final ASIC), the Vth line is not used locally. I have not updated the 
> schematic with this feature.
> 
> 3. We will use the same form factor for the anodes, i.e. 24 channels, so 
> we can use the same connectors and cables.
> 
> 4. Heat removal from each preamp card is effected by conduction via a 
> flexible copper wire of the required cross section and length (~10 
> inches) to a collector/radiator plate placed between the detector 
> packages and attached to the support rods/structure. The final design 
> has not been completed.
> 
> 5. Serviceability - all active circuitry must be easily accessible and 
> replaced to minimize experimental downtime.
> 
>     I am open to suggestions and I welcome any comments you may have. I 
> also suggest that we meet and discuss these issues further during your 
> visit to Jlab.
> 
> Regards,
> Fernando
> 
> 
> Gerard Visser wrote:
> > Hi Fernando,
> >     Of course, that's understood, that it is only a preliminary 
> > version at this stage. But if you have schematic and layout plots 
> > enough to have discussed them at the meeting, I think it would be 
> > interesting to see them... Can you post them to the portal (or send 
> > directly if you prefer)? In particular I'd like to understand the 
> > overall layout, and to see details on the pulser and pulser control 
> > interface, and the power scheme. I have some ideas for the pulser, 
> > using only the one extra pair in the 50-conductor cable to control it; 
> > I bought some parts but haven't had time to play with it yet. Perhaps 
> > I can try it next week. But maybe you already have a circuit worked 
> > out for this?
> >
> >     Gerard
> >
> > Fernando J. Barbosa wrote:
> >> Hi Gerard,
> >>
> >> I have not released the final version yet. Please note that this is a 
> >> study based on the prototype preamp ASIC. I am re-checking dimensions 
> >> as there is not much space available. I am also performing thermal 
> >> simulations which affect the final design.
> >>
> >> Regards,
> >> Fernando
> >>
> >> Gerard Visser wrote:
> >>
> >>> Is Fernando's preamplifier board design available/posted somewhere? 
> >>> It would be good to have a chance to comment on it. Thanks,
> >>>
> >>>     Gerard
> 

-- 
John Schaapman                   Ph: 780-492-3043
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