[Halld-tracking-hw] Tracking Meting Tomorrow

[Gerard Visser]

Hi Fernando,
	Thanks, I will change the gain setting as you say.
	Could you please still send me another board in CDC configuration? First of all 
this one is set for cathodes and I might not have enough 0402 jumpers to convert 
to anodes operation, and secondly this board has apparently all channels dead on 
the middle ASIC and I worry perhaps could have an abnormal response on the 
others (I don't know what the cause of the trouble is). In any case, having two 
boards to be able to confirm the measurements on the second unit, I think will 
be a good idea.
	If you have 'plenty' then please also send one in FDC cathode configuration 
(same reasons).
	I have updated my slide with a 2nd one showing the waveforms at the ADC output 
terminals. With the caveat this is as you say for quite the wrong gain selection 
on the ASIC, the results of this test look to me to indicate the linearity is 
really worse than it looks on the ADC125 view, the maximum reasonably linear 
pulse height is about 43% of full scale on the ADC. We'll have to see how this 
looks with the correct gain setting on the ASIC.
	My updated slides are here 
http://npvm.ceem.indiana.edu/~gvisser/GlueX/ADC_scale.pdf
	Sincerely,

		Gerard

p.s. And the answer to Curtis' question from the other day "Does the input of 
the FADC-125 match the 0V to 0.5V output of the ASIC, or is it something else?":
For pulses of this shape, the input of the ADC125 matches to an amplitude of 
990mV, which is indeed probably higher than intended (sorry). HOWEVER care is 
certainly needed - for _wider_ pulses the ADC125 full scale will be _lower_ in 
amplitude (it is a shaper...). [And I presume the CDC can get some pretty wide 
pulses when tracks pass at an angle.]


On 4/13/2011 2:54 PM, Fernando J. Barbosa wrote:
> Hi Gerard,
>
> The preamp you have is set for a gain of 3.2 mV/fC and a dynamic range of 110 fC
> (@ 5% linearity), quite different from the CDC. This is the fifth row in the
> Table 2 of GlueX-doc-1364 (the CDC is set as per the second row - 0.57 mV/fC,
> DR=380 fC).
>
> I attach the preamp configuration settings showing where the resistors are to be
> installed. To set your preamp to the CDC configuration, move the resistor to the
> left of the RC label to the pads on the right (5.1 Ohm resistor sets RC to logic
> 1) and move the resistor to the left of the HG label to the pads on the left
> (5.1 Ohm resistor sets HG to logic 0).
>
> The FDC cathode setting is the sixth row in Table 2 (2.6 mV/fC gain). Let me
> know if this works for you as this changes are easy to make with a soldering
> iron. If not, I will send you another preamp(s).
>
> There is GlueX-doc-1570 showing the dynamic range with the HVB and shows good
> linearity.
>
> Best regards,
> Fernando
>
>
> Gerard Visser wrote:
>
>
>> the preamp strapping picture (for current discussion)
>> http://npvm.ceem.indiana.edu/~gvisser/GlueX/straps.jpg