Minutes of the forward endcap EMC SeeVogh meeting, 17th of August 2015, 14:00-16:15
Bochum: Claudius, Fritz-Herbert, Malte, Miriam, Patrick, Tobias H., Tom, Cathrina, Malte, Matthias, Stephan
Assembly of more 'final' subunits:
We want to build two more 'final' type subunits (one VPTT unit, one APD unit)
There are 32 APD-preamps that can be produced in Basel on a short time scale (email from Werner on Wednesday after the meeting...)
The necessary 16 VPTT preamps can be manufactured within a few days
Malte is going to count the preamp boards we have in Bochum that can be modified to the latest versions
The gain (and hence the susceptibility to ringing) for the APD preamps needs to be determined first (need to do lab tests on different boards from Basel)
The impact of the size of the capacitors in the feedback loop of the VPTT preamps on their gain needs to be checked (several modified versions from Basel currently under test)
We plan to manufacture both versions more or less in parallel (depending on availability of components: preamps, APDs)
Claudius: Cooling scheme for ADC crates needed
Myroslav: Henk Smit is currently working on cooling and mounting structure, Rick will go on with this after vacation (end of August)
Drawings/ideas will be needed earlier than real parts: SeeVogh meeting dedicated to this issues on Thursday, 11 a.m.
Connector board sketch (signal cables to ADC boards per crate) shown by Christoph
After some discussion it turned out that even the power connectors to the ADC cards will fit to the board
The DC-DC power supplies for the ADCs may be mounted immediately behind the connector boards (or even on the boards itself?)
Real connectors and cables need to be ordered to check that all really fits
A reinforcement of the board may be needed to prevent it from bending or cracking while inserting and pulling ADC boards form the crates (metal bar across the board...)
There are currently five EMC ADC boards, two in forward endcap version for the readout of Basel preamps, three in barrel version for Apfel ASICs
The boards need to be debugged (some shorts) and may be fully functional before the September PANDA meeting at GSI
Latest tests and estimations by Pawel led to the conclusion that no shaping circuit may be needed but all preamp signal manipulation/feature extraction may be done by digital filtering only
Pawel presented a board with the two gain stages per readout channel differing by a factor of five only (rather than 16 as always used up to now)
We agreed upon the need for a higher factor between high and low gain than 5. Is 16 really needed/the optimum?
Gains can quite simple be adjusted by resistors in/around the input buffer preamps
As the ADC input range is +/- 1 V the ~2.2 V maximum output of the Basel preamps needs to be attenuated (x1)/amplified (x16) on the ADC board by the input buffer (maintaining 50 Ohms input resistance)
There is serious concern about the 'shaper-less' input stage (Basel, Bochum): Do we not block the higher gain branch with the long preamp signal for much too long time for small signals piling up on the clipping signal?
Would different approaches for inner and outer range (VPTT and APD region) help?
There is also concern whether the gain-bandwidth range of the currently used input preamp is sufficient (however, higher gain-bandwidth would result in higher power dissipation)
We definitely need to test, test, test this new boards in conjuction with the subsequent feature extraction (pileup recognition etc.), actually also on new beam times, as this is a complete new concept of signal treatment
Can we get the necessary hard and software besides the ADC boards on the September meeting?