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Testing of the TriP chip at DABJ. Estrada, C. Garcia, B. Hoeneisen, P. Rubinov

• First VLPC spectrum with the TriP chip• Z measurement using the TriP chip• Conclusion and plans

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…in case you do not know

• Two summers ago the design of AFEII started. AFEI does not work at 132 nsec (at that point 132nsec was still alive).

• A new front end chip (TriP: Trigger and Pipeline) was designed to replace the SIFT+SVX combination. The new system uses a commercial ADC for the charge readout.

• MCMII was designed for the TriP chip, MCMII mounts on the existing AFE. We have been using MCMII for 1.5 years, three existing versions.

• Last summer we received the TriP chips, they were mounted on MCMII and readout using the existing AFE (SASeq). Extensive tests of 8 chips were done in the bench (see DØNote 004009 and DØNote 4076), high yield ~90%. We have enough TriP chips for the full AFE replacement.

• This summer we have the 4-cassette cryostat to look at real signals from the VLPC.

3

Why do we still bother with AFEII?(132nsec is not a possibility anymore)

• The situation is as follows:– we have the TriP chip, we have enough of them.– we have seen that it works, and maybe it solves many of the

issues with AFEI (split pedestals, tick to tick variations).

• After some discussion with DØ management we agreed to:– build a real AFEII and populate it with 8 MCMII (J. Anderson)– at the end of the year, with the information from our tests and

our knowledge of the performance of AFEI, we will make a decision on the possible replacement of the CFT electronics.

4

VLPC spectrum

We have a high gain cassette (~55K in Don’s units), from our spares. Without seriously optimizing the parameters for the operation of the TriP in these conditions, we got a nice sprectrum. Notice the very little spread between channels and the uniformity in the gain.

VLPC signal with the TriP chip (132 nsec - cass 109, LH, @7.2 V)

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0 50 100 150 200 250

charge (ADC counts)

Same channels as seen by the stereo board, after very hard work to reduce the noise.

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Fits to the spectra

Mysterious deformation around 128 counts

We measure a gain of around 21 counts/p.e., from our previous studies of the chip we believe this means that the VLPC are running at ~75K, a bit higher than what we were expecting…

Other typical parameters: pedestal width=0.18 p.e., gain dispersion=0.17 p.e., pedestal spread (RMS-16 channels)= 0.05 p.e.

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Z measurement

The TriP seems to be working, we will keep testing it to have the information to make the correct decision in December.

One idea: a minor modification to the TriP that would allow us to measure the time when the discriminators fired with respect to the crossing clock , (see DØNote 004009) . This will give a measurement of the Z position of the hit along the fiber, could help for tracking (tracking algorithm experts need to evaluate how useful this will be).

We are now measuring the resolution that we can achieve for this z measurement using the current version of the TriP (we can only look at ½ the channels of the TriP and we needed to implement an external readout for the timing).

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Cosmic Muon Trigger

scope

SASeq

ethernet

AFEII-prototype

VLPC

bit3ADC information

timing information

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Our events

DISCR. from TriP

CROSSING(132nsec)

SCINT.1SCINT.2

This is how me measure timing of the discriminator, with respect to the muon trigger. The green line is the OR of 16 channels.

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Our signal

We do no seem to be getting a lot of light, but we get some.

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Results

Combining the results of 32 channels (2 TriPs), we see that we can only have a timing measurement when the total (direct+replected pulse) number of photoelectrons is above ~5. Our threshold is here is around 1.5 p.e.

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Results, with a cut at 5 p.e.

The width of the peak is about 4 nsec wide, and there is a tail that makes the RMS 6.2 nsec. This could come from muons at large angle that have a different Z

12

Results as a function of the cut in the ADC

we start to get a measurement only above 5 p.e., and seems like for the large signal pulses we get about RMS=4.5 nsec.

13

Changing the TriP operating parameters (programmable registers).

We changed the TriP operating parameters to see if we could improve our resolution. Things got a little bit better, improving by 1nsec for large number of photoelectrons. Did not re-calibrate the VLPC with this new parameters.

3.5 nsec x 16.6 cm/nsec = 58.1cm

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Conclusion and Plans

• The TriP still looks good. The noise and the channel to channel differences look ok (so far we looked at a small number of channels). It is amazing how easy it is to operate this chip compared to SVX+TriP .

• For the moment we get σ=58cm for the Z measurement of the hit in the fiber. Things are a not as good as we where hoping for, we will continue trying to understand if this is the best we can do (part of this resolution could come from cosmic muons at large angle, that actually have a different Z).

• When Paul gets back we will move to 396 nsec, the performance of the TriP has not been studied in detail with this timing…