[Halld-tracking-hw] Tracking Meting Tomorrow

[Fernando J. Barbosa]

Hi Gerard,

OK, I will send you two preamps (CDC and FDC).

There is an easy way to double the pulse amplitude at the input of the 
ADC which is to remove the back-terminating resistors on the preamp 
card. This would not change the preamp response . This change would not 
require any changes to the fADC125 and one version would still fit both 
detectors as this is already the consensus at JLab. I can send a preamp 
to Naomi in this configuration for tests.

Best regards,
Fernando



Gerard Visser wrote:
> 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
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