[Halld-tracking-hw] new preamp

[Gerard Visser]

Hi Fernando,
	I agree, you should go forward with this new plan for the CDC to use preamp 
boards without the source termination resistors. It certainly does double the 
gain (of course), and it looks like the reflection is on the order of 1.5%. That 
can produce some error (especially in the timing measurement),  but I guess it 
is an acceptable error. There would only be an error in case of the second of 
two pulses separated by 200 ns or less, and would the timing algorithm work in 
such a case anyway?
	One thing which we have to keep in mind, the common-mode impedance seen at the 
ASIC outputs will now be ~500 Ohms rather than ~25 Ohms. This should be ok, but 
if there is some external common-mode pickup that produces a common-mode voltage 
at the ASIC, since the transistors have a not large finite output impedance this 
will couple to a differential voltage on the line. I don't think it will be a 
problem, but there is less immunity to such an effect with the source 
termination resistors removed.
	It seems like the way to go, however. I will make a more careful linearity plot 
with the termination present or removed on the same channel, just to confirm. 
But you have already done this, no need to wait for my plot.
	Sincerely,

		Gerard

On 4/26/2011 11:44 AM, Fernando J. Barbosa wrote:
> Hi Naomi,
>
> That's great news!
>
> Gerard, do you concur?
>
> Thanks and best regards,
> Fernando
>
>
> Naomi Jarvis wrote:
>> Hi Fernando,
>> >From what I have done so far, it looks absolutely fine. Did you hear anything
>> more from Gerard? My vote is to go ahead with it.
>> Best regards,
>>
>> Naomi.