[Halld-pid] trigger electronics

[Alexander Ostrovidov]

Hi Beni,

Indeed, your setup looks more logical. Actually, this is a setup
I  was thinking of using initially. However, the reason I went
with my current scheme is very simple - it provides the fastest
ADC gate possible. Even in this case, I have to delay 6 PMT 
signals by 130ns to be at proper time. This is about 100' of cable 
on top of another 50' from detector to the first splitter for a total 
of 150 feet. I guess this is already longer than we'll ever need for
the real detector in the hall and with flash ADC.

What you are suggesting will add extra delay to the ADC gate
due to delays in the extra path elements between the main
coincidence and the second one (the one you replaced with fanout):
1) delay in NIM-ECL; 2) delay in TI; 3) delay in ECL-NIM; 4) all extra
cables in between. We are talking about something like extra 40-60ns,
or 30-45 feet of extra cable length. Actually, exactly 50' because
that the length of the cables we have, and I don't want to start 
cutting them without good reason.

I have such NIM-ECL to TI to ECL-NIM path anyway. However, it is
not used to propagate (and delay) the front of the trigger/gate. Rather,
it is used to block consequent triggers after the first one by flipping
TI latched level until it is reset by DAQ. That's a purpose of the second
coincidence, and 50ns delay for this purpose is even desirable.
 Basically, instead of routing trigger signal on a long way through TI
logic,  I bring TI logic right to the trigger signal at the second
coincidence. And save 50' of extra cable length for each channel 
this way.

Sasha

On Monday, March 28, 2011, Beni Zihlmann wrote:
> Hi Sasha,
> I attached a pdf file with some red maker to indicate some issues I have
> with
> your trigger electronics.
> If I understand correctly then the red circle indicates the main trigger
> coincidence,
> namely a coincidence between top left/right and bottom left/right
> trigger paddles.
> This trigger signal should directly go to the TI input as trigger. The
> output of the TI
> is then the accepted trigger and should be used in the fanout to
> multiplex and
> be used for the ADC gate and the TDC trigger. The signal
> output of the trigger coincidence (red circle) should go directly into
> the TI and not
> making a coincidence between the trigger and the TI trigger accept. That
> does not
> make any sense. I indicated with red crosses (x) which lines should be
> removed
> and where the trigger (red line) should go.
> 
> I hope it is clear what I try to say.
> 
> cheers,
> Beni