atlas sct/pixel tim fdr/prr28 july 2004 resonant triggers - matt warren1 physics & astronomy hep...

28 July 2004

Resonant Triggers - Matt Warren 1ATLAS SCT/Pixel TIM FDR/PRR

Physics & AstronomyHEP Electronics

Matthew WarrenJohn Lane, Martin Postranecky

Resonant Triggers

ATLAS SCT TIM FDR/PRR28 June 2004

28 July 2004


Background

• This is based on work by Tony Weidberg and others detailed in a paper submitted to NIM.

• First seen on CDF

• Triggers generate large variations in current in the wire-bonds of some FE components as they read-out.

• Triggers at rates close to the mechanical resonant frequency of the wire-bond can cause it to oscillate to breaking point.

• ‘Normal’ running OK as triggers are random.

• Calibration/Test runs can easily generate triggers at fixed frequencies – even machine runs - LHC 1 or 2 bunches = 11.2/22.4 kHz

• Work has been done to evaluate the effects of this problem on the SCT.

28 July 2004


Experimental Results

• Resonances seen from 15kHz – 90kHz.

• Failures observed after a few minutes.

• Found NOT to have large affect on SCT – barrel orientation good, end-cap uses very short bonds

• But may have implications over the life-time of detector. Current frequency 17 kHz - on

resonance

Photo showing a wire-bond with a current of frequency 15 kHz - off

resonance.

• SCT like wire-bonds were operated in a magnetic field (1.8T).

28 July 2004


Role of TIM

• ‘Problem’ hard to fix - components are well into production– need to use ‘avoidance’ techniques.

• TIM is well located in the trigger tree.– Within SCT sub-detector.– Near top – a TIM fans-out trigger to 100s of modules.– Passes ROD Busy back to CTP - can provide back-

pressure.

• TIM also source of repetitive triggers – Trigger oscillator.– Bursts of CALs

• TIM can provide SCT biased monitoring information on trigger rates and veto periods.

28 July 2004


Fixed Frequency Trigger Veto (FFTV)

• ‘Proof-of-concept’ system developed to verify both functionality and FPGA resources consumed.

• Implemented in TIM FPGA2.

• Uses enhanced version of CDF algorithm:– Compares successive trigger periods, increments

counter if matching (within programmable ‘tolerance’).– Generates a Veto when match counter hits preset limit.– Period Max setting allows passing of low-freq triggers.– Period Min setting allows high frequency trigger ‘noise’

to be ignored.

• Result: Works! – Small: <100 ‘slices’ out of 6900 on Xilinx Spartan II

600E– Easy to reconfigure

28 July 2004


FFTV System Simulation

Note: High Freq component ignored

Freq<min Freq in window

Trig

Period Max

Period Min

Period

Period Match Threshold

Period Match Count

Veto

28 July 2004


Going Forward

• Sub-detectors should not veto triggers– (e.g. What happens to trigger number?)

• After discussions with Level 1 Trigger:

In ‘Run-Mode’ TIM must:– Not Veto any triggers, but assert ROD Busy instead– Count the time this Veto-Busy was asserted– This will ensures L1IDs are in sync.

In ‘Stand-Alone-Mode’: – TIM will veto triggers at source– L1IDs numbers then stay in order

28 July 2004


Implementation

• 2x 48 bit busy clock counters added– 81 day rollover.– Count Overall-busy and Veto-busy.– Reset by VME write.

• Setting based on experimental/calculated values:– Number triggers before Veto: 10– Cut-off Values: Min 15kHz, Max 75kHz.– Veto Period: 1ms.

• Based on “toy” Monte Carlo by Tony Weidberg predicting contribution of a deadtime fraction of 3x10-8.

• Test Results:– Using 100 60kHz triggers we see 17% pass-through.

• This agrees with theory.– Still small (<200 slices) and easily configurable.

28 July 2004


Outstanding Questions

• Does the Veto continue until fixed-freq. triggers stop, or are small bursts allowed through?

• Over-ride trigger in Run-Mode?– What happens if we still see ‘dangerous’

trigger even though we have asserted a ROD Busy?

• Should we be able to disable it in software?

atlas sct/pixel tim fdr/prr28 july 2004 resonant triggers - matt warren1 physics & astronomy hep...

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