J. Estrada - Fermilab 1

AFEII in the test cryostat 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

(more detail about the electronics in Paul’s talk)

MICE Fiber Tracker WorkshopFermilab

July 15, 2003

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Short history of AFEII

• 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.

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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.

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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)

0

500

1000

1500

2000

2500

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

Discriminator signal

AD

C in

form

atio

n

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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 and the crossing clock. The green line is the OR of 16 channels.

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Charge injection, integration window

The TriP has an internal mechanism to inject charge in any channel. We used this system to inject 60 and 30 fC (~ 7 and 3.5 p.e.) at a ramdom time with respect to the 132 nsec crossing to see the integration window and the internal timing resolution in the TriP discriminator.

t1= time from crossing clock to charge injection

30 nsec

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Charge Injection, timing resolution in the TriP.

A)

B)

C)

A) The time walk of the discriminator as a function of injected charge is very small.

B) The timing spread in the discriminator is 420 ps for 60 fC.

C) The timing spread in the discriminator is 662 ps for 30 fC.

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Integration window

We open a 30 nsec integration window and scan it with respect to the 132nsec clock.

Looking at the average signal (ADC output) we determine position for the optimal integration window, and we use this window to measure the timing resolution.

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Signal with muon trigger

T4= time from crossing clock to muon trigger

For events outside this window the charge does not get completely integrated in the TriP and we could be missing the first photons from our signal.

This data corresponds to 2 different runs, our setup had a timing problem during the first run that made us miss part of the interesting events.

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Our signal

We are using the 11m waveguides, and are getting in average approx. 5 p.e.

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Time walk

The photons from the scintillating fibers have some timewalk (~0.83 nsec/pe), we correct for this timewalk.

As the number of photons increases the timing spread reduces.

The integration window cut is already applied to this data.

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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 3.3 nsec. This could come from muons at large angle that have a different Z

Corrected discr. timing (nsec)

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Results as a function of the cut in the ADC

we start to get a measurement only above 5 p.e., and for the large signal pulses we get about RMS=2.8 nsec

(2.8 nsec x 16 cm/nsec = 48cm)

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Result for different timing

The integration window, according to the ADC, shows a plateau in the width of the timing distribution.

When pulses are delayed the spread becomes larger because we start missing the first photons.

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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=48cm for the Z measurement of the hit in the fiber. 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). We are waiting for input from our tracking experts to tell us how useful will this information be for track reconstruction ( reduction of fakes, reduction of CPU time for tracking algorithm, resolution improvement).

• Now moving to 396 nsec operation of the TriP, the performance of the TriP has not been studied in detail with this timing…