Re: Frontend & Thermal Management HallD

["Fernando J. Barbosa" <barbosa@jlab.org>]

Hi John,

    Thanks for your feedback. The present version of the preamp card, a 
study really, was primarily designed to get a baseline on the dimensions 
and the thermal performance based on the channel density. Let me address 
each of your questions:

2) Mitch has updated everyone on this topic.

3. a) I understand that we may have two or three versions of preamp 
cards but I believe a basic architecture is very desirable and possible. 
Curtis also communicated that the CDC electronics won't be in the gas 
volume.

b) Certainly the number of pins is limited, now. However, I don't expect 
a crosstalk problem with the input connector. If you consider a ground 
plane under the connector pads, 1 mm pitch, input impedance of the 
preamp and input signal current, the di/dt and dv/dt signal components 
are very low which imply very low crosstalk. What concerns me a bit is 
perhaps ground bounce due to the GND impedance to the supply 
distribution on the translator PCB. Also, keep in mind that the whole 
amplifier chain is differential and should keep load currents reasonably 
constant.

    Having said all this, the overall width of the card is set by the 
output connector and a wider input connector is available with 
additional pins available for GND, power and any additional control 
lines, if needed. There are a few other connectors that I am considering 
but I need to have updated drawings of the detector to properly suggest 
them.

4) That's a good point. I believe Joe Beaufait also asked me this 
question as he is planning the power distribution and routing. The 
cooling scheme, as presently suggested, needs some improvements. I 
certainly would not like to operate the ASICs at or near Tj=100 C. Any 
additional heat from the regulator due to increased drop would cause Tj 
to increase at steady state. Given the models that I already have, I can 
simulate a maximum input supply in a fashion similar to what I have on 
the report.

Thanks and best regards,
Fernando

John Schaapman wrote:
> Hi Fernando,
>   I have just a few comments on your excellent report.
>
> section:
>
> 2. The ASIC preamp.
>    Has Mitch Newcomer indicated that the previously mentioned submission 
> date to MOSIS of Feb 12 will be missed and why?
>
> 3. The Preamp Card
>    a) I'd just like to clarify that two versions of the 24 channel card 
> will still be required due to the fact that the input signal polarities 
> of the anodes and cathodes are opposite. A third version may be needed for 
> the CDC if it is in the chamber gas and requires low outgassing material.
>    b) The input connector could be a source of problems since there are 
> not enough signal grounds. Adjacent signal pins could create unacceptable 
> crosstalk and too few grounds could lead to signal reflections and more 
> crosstalk. I realise that there is very little space but this arrangement 
> should make us nervous.
>
> 4. Thermal Management.
>
>    You have specified a power supply input of 3 volts minimum for operation and
> your thermal calculations so far. It would be nice to know at some point what
> the maximum supply voltage would be due to thermal limitations. This would help
> set the tolerances required for the power supplies and distribution system.
>
> John
>
>   
>
>   
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