[Halld-tracking-hw] New preamp

[Fernando J. Barbosa]

Hi Yves,

Yves Van Haarlem wrote:
> Hi Fernando,
>
> I have a suggestion below,
>
>>> My other concern is over the mapping of the preamp channels through 
>>> the cable.  We are now using the new preamp and new cable with the 
>>> old HV board.  The correspondence between the numbering on the HV 
>>> board and the preamp channels has changed.  Is this now the final 
>>> mapping?
>>>
>>> Previously we were using the cable with channels 1-8 and 17-24 
>>> feeding into the shaper unit, which has 16 channels total, and then 
>>> into two 8-channel fADCs.  The chamber prototype is configured so 
>>> that the missing 8 channels correspond to the straws along 2 sides 
>>> of the chamber; the two groups of 8 channels in use correspond to 
>>> two blocks of 8 straws, one above the other. With the new cable it 
>>> seems that we now have access to the 8 channels which were missing 
>>> before (along the edge), but since we only have 16 channels from the 
>>> shaper, we have lost access to one block of 8 straws.  This makes 
>>> cosmic ray tracking much slower, since we are looking for tracks 
>>> passing through at least 4 straws.  This is hard to explain without 
>>> a diagram but the effect is that the configuration of our available 
>>> channels is much less as efficient than before.  This will be solved 
>>> when we have a 72-channel fADC; alternatively we could just use the 
>>> old cable until the new fADC is available.
>>
>> The old preamps (also designed for 24-channels) had only two chips 
>> installed (on top) because the ASIC package was not reliable for 
>> assembly on the bottom (it had a removable lid in case we needed to 
>> probe the die). The preamp card has channels 1-8 from one chip on 
>> top, 9-16 from bottom chip and 17-24 from the second chip on top. 
>> Because of the 16-channel readout on the shaper, the cable (old 
>> cable) was modified at the ERNI connector (connects to preamp) to 
>> read channels 1-8 and 17-24. This is the reason for what you observe 
>> with the new cable. This won't be the case with the 72-ch fADC125 
>> because it reads from all 24 channels on a preamp card. Yes, please 
>> you use the old cable with the new preamp and shaper for your 
>> immediate tests and then use the new cable when the 72-ch fADC125 
>> becomes available (late April).
>
> Once it is decided which group of 8 channels goes where on the cable 
> (between HV-board and fADC), could you modify the labeling of the 
> channels on the HV board so that channel 1 -> 24 on the HV-board 
> corresponds to channel 1 -> 24 on the fADC (or 25 -> 48; or 49 -> 72). 
> We might avoid a lot of confusion in the future.
Certainly, I will re-label the channels on the new HVB now that the 
numbering is final.
>
> The difference in mapping between old and new cable in a table:
>
>
> Ch# on HV board || ch# on old cable  || new cable  || fadc#
> 24              || 1                 || 1          || 1
> 23                 2                    2             2
> 22                 3                    3             3
> 21                 4                    4             4
> 20                 5                    5             5
> 19                 6                    6             6
> 18                 7                    7             7
> 17                 8                    8             8
> 16                 9                   17 ! 15                
> 10                   18
> 14                11                   19
> 13                12                   20
> 12                13                   21
> 11                14                   22
> 10                15                   23
> 9                 16                   24
> 8                 17                    9 !           9
> 7                 18                   10            10
> 6                 19                   11            11
> 5                 20                   12            12
> 4                 21                   13            13
> 3                 22                   14            14 
> 2                 23                   15            15
> 1                 24                   16            16
>
>
> So the possition of two chips have been swapped on the cable, was this 
> deliberate?
As I mentioned on my previous email, we only had 2 chips installed on 
the old preamp and the old cable was modified at the ERNI connector 
(swap on the cable at the connector) to read these two chips into the 16 
channel shaper. So, you only read HVB chs 24-17 into chs 1-8 and HVB chs 
8-1 into chs 9-16. Sorry, your table was a bit scrambled.

Best regards,
Fernando


>
>
> Best regards,
>     Yves
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