Re: Electronics Readout Characteristics

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

Hi Gerard,

Thanks for your reply. My answers follow:
>     Are both you and Yves using identical length of the signal cable? 
> That will of course make a difference.
The cables are all 18 meters long.
>     I have some small questions on your document. In fig 2, you show 
> the voltage (peak-pedestal) out of preamp as a function of input 
> charge. What is the cable length (and type) when this measurement is 
> made? Is the measurement made with a differential probe or w/ 2 
> single-ended probes and scope math? What is the error on charge values 
> here, i.e., what is the error on the 1pF capacitance value (probably 
> 20-30% I suppose... Unless you have gone to great lengths to calibrate 
> it somehow.) What is the signal input transition time (should be <3 ns 
> I think, or it will affect the calibration of this).
The cable attached to the preamp was 18 m and terminated by the shaper. 
I used two high-Z probes and the math function at the output of the 
preamp, on the connector pads. The cap, as you point out, is about 20% 
tol . I did not go to great extents to calibrate the input charge very 
accurately but the numbers agree reasonably well with yours and Mitch's 
results if you take the output loading into account. The rise time of 
the pulse input was 1.7 ns. Another reason for figure 2 was to get the 
transfer curve of the preamp well into the non-linear region and observe 
its behavior under high input charge conditions - it behaves very 
gracefully.
>     As a practical suggestion, how about if Yves were to send his 
> shaper board to you and you send one of the FDC anode ones to Yves. 
> That should settle this unambiguously.
That's a good idea. I will ask Yves to send me his shaper and then make 
any necessary changes. I will also send you a preamp.

Thanks and best regards,
Fernando




>     Let me know what I can do to help further,
>
>     Gerard
>
> p.s. Please send the partly-dead preamp board to me when you have a 
> chance, I will need to make some tests again soon. Thanks!
>
> Fernando J. Barbosa wrote:
> > Hi Gerard,
> >
> > I know you are busy with the fADC but I just want to check some info
> > with you.
> >
> > We have measured the gains for the shapers and are as follows: FDC
> > anode=2.16, FDC cathode=10.42 and CDC anode=3.2. The first two
> > measurements are outlined in my recent GlueX-doc-1065; Yves got the
> > number from his measurements posted on the wiki log.
> >
> > Do these numbers agree with your specs? Because there is some 
> saturation
> > at the ADC on the CDC, I suggest we change the gain on that shaper to
> > the same as the FDC anode shaper.
> >
> > Regards,
> > Fernando
>
> Fernando J. Barbosa wrote:
>> Hello everyone,
>>
>> I have completed systematic characterization of the readout electronics
>> for the tracking chambers and I have placed a document on the portal
>> (GlueX-doc-1065). It can be easily accessed through the electronics wiki
>> at http://www.jlab.org/Hall-D/software/wiki/index.php/Electronics.
>>
>> Gerard, could you confirm that the CDC receiver/shaper has the same
>> characteristics as the FDC anode shaper?
>>
>> Regards,
>> Fernando
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