Re: FDC meeting minutes

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

Hi John,

    My intention is to have the mode selection done on the preamp board, 
either by jumper or by resistor (pull-up or pull down?). As you know, 
this is preliminary and came up with correspondence with Mitch and it is 
not yet implemented on the ASIC.
    As for an external control for the anodes, it could be implemented 
by distributing a logic level via the translator boards. However, the 
number of pins for the preamp cards is already limited and I would 
prefer to have this function also set by hardware. Perhaps a jumper 
would be the best option as one would have to choose between either 
using a TDC or an ADC for readout.

Regards,
Fernando

John Schaapman wrote:
> 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
>>>>>           
>
>   
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