Preamp discussion

["Fernando J. Barbosa" <barbosa@jlab.org>]

Hi Mitch and Gerard,

I have a few items that I would like to bring to your attention and 
which are based on previous discussions:

1. Preamp Costs - For the prototype run of 40 Die, the Mosis cost is 
$21.5K for the assembled parts. What would the cost be for 2500-3000 Die 
and assembled parts?

2. Package - I agree with using a 64 pin package as it provides for 
additional power, ground and additional pins not yet defined (if 
needed). However, I would like to suggest the use of the QFN64 (64 pin, 
ground-paddle, 0.5 mm pitch). This package provides improved thermal 
characteristics compared to the LQFP64. The preamp cards on the FDC (and 
most likely the CDC) will be installed in regions with very limited 
space and most of the heat will be removed by conduction to some sort of 
detector cooling assembly (not yet defined). I2A carries this package as 
standard.

3. Double termination - Given the thermal limitations, I agree that 
there should be no termination resistor on the package. I also see no 
need for double termination on the card as we already have differential 
lines and the SNR may actually be adversely effected with the double 
termination given the long cable runs.

4. I should have a preliminary diagram for the preamp card soon. I 
should also review an old FDC electronics diagram that I distributed a 
long time ago.

5. I would also like to request a number of the prototype packaged 
preamps for assembly on this new preamp card as soon as they are 
available. We can quickly test them on the prototype FDC on site. Maybe 
10 would be more than enough.

6. A 24-channel board is fine per Gerard's calculations. I still need to 
check the spacing required on the FDC (connectors and such) due to the 
plane-to-plane pitch.

7. A detector test pulse system is a must and we need to discuss this 
soon. There are pros and cons to having the pulser on-board the preamp 
card or external: power, compactness, flexibility (amplitude 
adjustment?), cabling, etc. Capacitive coupling to the preamp inputs via 
orthogonal traces is a simple and effective way of injecting some fixed 
charge.

Best regards,

Fernando

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