[Halld-tracking-hw] New preamp

[Yves Van Haarlem]

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.

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?


Best regards,
 	Yves