Re: Hall D electronics update

[Gerard Visser <gvisser@indiana.edu>]

Hi Dan,
	Are there any specifications or preliminary sketches of Fernando's 
preamp board available?
	I am in particular wondering whether it might be a 24-channel (3-ASIC) 
board, and have an on-board pulser digitally controlled by the 25th pair 
of a 25-pair cable going to the ADC boards. Simon and I have discussed 
this somewhat.
	I think that a 24-channel board is better than a 16-channel board because:
	- It gets slightly closer to the channel count per plane you have 
originally specified (I'm looking at GlueX-doc-412-v17 for this). 119 
anodes per plane becomes 8x 16-channel boards (128 ch) or 5x 24-channel 
boards (120 ch). 238 cathodes per plane becomes 15x 16-channel boards 
(240 ch) or 10x 24-channel boards (also 240 ch).
	- It reduces by 33% the number of power connections needed.
	- It reduces by 33% the number of signal cables and by approximately 
11% the cable tray cross-sectional area.
	- It matches to a 72-channel ADC board with three input connectors. I 
believe this layout would work very well, with every other input channel 
routed up to a mezzanine board, 36 ADC channels on the main board, 36 
channels on the mezzanine board. If the channel granularity is 16, it 
may not be possible to have more than 64 channels per board. Using the 
channel counts above, the 16-ch per cable system would require 228x 
64-ch boards in 12 VME crates. The 24-ch per cable system would require 
200x 72-ch boards in (exactly) 10 VME crates.
	Of course, there are considerations about the anode and cathode plane 
design and the preamp board mounting, that I am not informed to judge 
right now.
	Let me know what you think, thanks.

	Gerard

p.s. Let's please get these discussions on the 
halld-tracking-hw@jlab.org list...

Daniel S. Carman wrote:
> 
> Jim,
> 
> I wanted to give you a heads up on work going on at JLab for the
> FDC preamplifier daughter boards.  ...