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Some more preamp questions



Hi Mitch,

GAS - GlueX Amplifier Shaper sounds like a good part name. I will add a 
number so people don't confuse its name with a real gas. What about 
GAS-1? You are the author!

1. COST - I have been contacting Sandy Connolly at I2A and she sends 
regards to you. She provided me with information on the LQFP-64 and 
QFN-64. The thermal resistance for the QFN-64 is on average about half 
as that of the LQFP-64 but may not be a factor (soon I will go over the 
thermal simulations). The packaging costs are the same. Sandy's cost 
estimate for the production packaging, which includes wafer dicing, 
handling, wire bonding, etc, is $2,560 for 4K parts and $250 for the 
bond diagram generation if needed. She also quoted me $1,500 for the 40 
part prototype run.

The total production cost is $84,000 for 4K DIE from TSMC plus $2,560 
for packaging 4K DIE plus $250 for the bond diagram generation or $86,810.

2. PINOUT -  I am including a pdf file that shows the preliminary pinout 
for the GAS-1 and following your recommendations from an earlier email. 
Any changes?

3. Referring to Millind's Powerpoint document dated 11/11/2006, page 23, 
the plot shows the differential output response for two input amplitudes 
and at 2.4V, 2.5V and 2.6V supply voltages. The amplitude variation with 
supply (PSRR) at low amplitudes is about 5-20% and at higher amplitudes 
it is 50-60%. For this variation to be much less than the non-linearity, 
say 1% from chip-to-chip, the power supply at the chips must be +2.5V 
+/- 10 mV. This necessitates the use of linear regulators on the preamp 
cards which is not a problem. How does the linearity change 
(sensitivity) with the supply?

4. Page 24 shows the differential amplitude variation with temperature. 
I believe this is for a 50 degree C range. For the 100, 200, 300 input 
amplitudes the variations are 10.2%, 3.5% and 9.9%, respectively. As 
above, how does the linearity change with temperature? What were the 
junction temperatures for your simulations?

5. Page 29 suggests pin selectable comparators. There have been some 
questions concerning the use of discriminators/TDCs on the FDC anodes. 
We don't have enough pins on the 64-lead package for accommodating both 
differential analog and discriminator signals simultaneously and I 
believe we don't need both types of outputs simultaneously. We also need 
to keep the package size in check (~10mm x10mm) as there is limited 
space. If it is possible to add the discriminators in a transparent 
fashion and use the same output pins as the analog outputs , we would 
need to enable/disable the discriminators circuitry. How difficult would 
it be to add this extra feature? The cost would also go up with the 
additional Si area.

Thanks and best regards,

Fernando


GAS Pinout.pdf

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