[Halld-cal] Spare BCAL readout board

[Elton Smith]

Hi Fernando and Chris,

Thanks for getting the new BCAL PCB assembled and tested. I am not quite 
sure I understand your testing procedure, but perhaps your updates will 
result in a more robust circuit. If you have time, perhaps you can come 
to the Bcal readout meeting at 11:00 this morning and we can go over 
this. There will be an extended opening in Hall B on Thursday, which 
might be a good time for this change if we decide to go forward with it.

I think reducing the gain of the TDC channel by a factor of 2 is very 
reasonable.

If we are to replace one of the circuits on the Bcal, I suggest we 
replace the downstream side. We believe that this side has a poor 
thermal contact between the cooling tube and plate. If we pull it out, 
this could be verified and perhaps repaired at the time the board is 
exchanged.

Thanks, Elton.



On 4/16/12 11:27 PM, Fernando J Barbosa wrote:
> Hi Elton,
>
> The spare BCAL PCB has been assembled. I tested it first with the 
> input resistive network as installed on the two BCAL readout modules 
> and then with optimized values. These also decrease the susceptibility 
> to ground noise caused by large signals on adjacent channels. Although 
> I could not observe any ringing, before and after optimization, 
> coupling due to GND and power dips is much improved. The final design 
> will employ thicker copper (we have 0.5 oz on the internal layers and 
> these will be increased to 1 oz or 2 oz). I have tested all the 
> channels and all look good.
>
> I propose to replace the readout board on one of the BCAL modules with 
> the optimized spare. This is the quickest way to verify its 
> performance for ringing. I also propose to decrease the gain of the T 
> outputs by a factor of two to X5 as we discussed. Let me know if you 
> are in agreement and then let me know which module you would like to 
> refurbish as we will need to set the bias jumpers for the SiPMs. Once 
> this is done, it should take less than a day to replace the board and 
> test the full module.
>
> Best regards,
> Fernando