Physics & Astronomy HEP Electronics

1. Physics & AstronomyHEP Electronics Resonant Triggers ATLAS SCT TIM FDR/PRR 28 June 2004 Matthew WarrenJohn Lane, Martin Postranecky Resonant Triggers - Matt Warren

2. 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. Resonant Triggers - Matt Warren

3. Experimental Results • SCT like wire-bonds were operated in a magnetic field (1.8T). • 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. Photo showing a wire-bond with a current of frequency 15 kHz - off resonance. Current frequency 17 kHz - on resonance Resonant Triggers - Matt Warren

4. 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. Resonant Triggers - Matt Warren

5. 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 Resonant Triggers - Matt Warren

6. 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 Resonant Triggers - Matt Warren

7. 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 Resonant Triggers - Matt Warren

8. 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. Resonant Triggers - Matt Warren

9. 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? Resonant Triggers - Matt Warren