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Optical links in the 25ns test beam

Explore the comprehensive setup of optical links at the 25ns test beam area including analog and digital components, gain factors, and dynamic range measurements. Gain insights into noise contributions and link attenuation in this advanced system design.

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Optical links in the 25ns test beam

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  1. Optical links in the 25ns test beam Karl Gill CERN Acknowledgements: O-link and MIC teams

  2. CMS Tracker readout and control links • Final system Analogue Readout 50000 links @ 40MS/s FED Detector Hybrid Tx Hybrid 96 Rx Hybrid processing MUX A buffering APV 4 DAQ 2:1 D amplifiers 12 12 C pipelines 128:1 MUX PLL Delay Timing DCU TTCRx TTC Digital Control 2000 links @40MHz FEC Control 64 4 TTCRx CCU CCU 8 processing buffering CCU CCU Back-End Front-End

  3. X5 system test setup • In the beam area: • 4 modules, each including: • Si detector • 4 APV6 chips • CCU card • TRI card • analogue optical link • timing/control ring • digital links to/from control ring

  4. X5 analogue o-links - transmitter • 4-channel laser package • 4-channel analogue laser driver chip • 4-ch transmitter daughter card 4-way laser package

  5. X5 analogue o-links - fibre • single mode optical fibre: • 4-way ribbon pigtails at Tx, Rx • 12-way fibres ribbons • with 12 way MT connectors • using only the 4 central fibres • 96 fibre cable • 8x12 ribbons 96-way cable and 12-way optical ribbon and MT-connector

  6. X5 analogue Links - receiver • Receiver side: • optical ribbon connectors • 4x 4-way receiver card • jumper cables to FED input 4-way receiver daughter-board

  7. X5 digital links • 2 x 2-way transmitter and receiver • one unit located next to FEC, another inside beam area

  8. CMS Tracker readout and control links • Final system Analogue Readout 50000 links @ 40MS/s FED Detector Hybrid Tx Hybrid 96 Rx Hybrid processing MUX A buffering APV 4 DAQ 2:1 D amplifiers 12 12 C pipelines 128:1 MUX PLL Delay Timing DCU TTCRx TTC Digital Control 2000 links @40MHz FEC Control 64 4 TTCRx CCU CCU 8 processing buffering CCU CCU Back-End Front-End

  9. Analogue readout chain (without optical link) • TRI-card to FED (e.g. with copper link) from APV • APV output 50mA per MIP • 120mV into FED per MIP (for link gain = 1) • +/- 750mV FED input range equivalent to 12.5MIP

  10. Analogue optical link • Each component contributes a gain factor: fibre/connectors laser photodiode receiver laser driver • Expect spread of optical link gain (2.5-4.0 overall): • losses at optical connections • variation of laser, receiver efficiency • Will have programmable gain compensation in final links

  11. Nominal Optical vs Cu link gain Vin at FED (mV) Go-link =2.5-4.0 1500 GCu-link=1 1000 500 0 0 2 4 6 8 10 12 signal (MIPs) • Limited dynamic range (~4MIPs) for nominal o-link gain • Note, in final system Go-link will be ~1

  12. Link gain attenuation • Potential divider added to attenuate input to link • Different values of R tried in X5 • R=27W (A=21%), 91W (A=48%), 200W (A=66%) • test effect of spread in gain on system • noise penalty with large gain in optical link

  13. Full chain • Schematic of full analogue readout chain current offset attenuation laser dc bias Receiver output offset • link integration: • connection then setting of gains and offsets • setup/calibration should be made automatic in future • 16 (+4) readout channels instrumented in total

  14. Gain + offset settings from TRI to FED • e.g. for R=91W adjustable TRI dc baseline Tick 210mV -600 -300 0 +300 +600 Vout (TRI) Tick 105mV X 0.50(adjustabledivider, R=91W ) Vin (O-link) -400 +400 adjustable laser dc bias-point X 3.0 (link-average) Vout (O-link) -1200 +1200 Tick 315mV Vin (FED) adjustable receiver output dc offset +750 -750 FED output 0 256 512 Tick 110 counts Offset + gain settings should be automated in future

  15. APV analogue biaspoint Vin FED (mV) 1500 overall ± n MIPs dynamic range digital header + pipeline addr. 1000 VADJ 500 tick analogue data 0 Time (a.u.) • Vadj at APVs set to correspond to 0V into FED • 0V was ~256 ADC counts

  16. Measured gain: link + divider • based on tick marks at TRI and receiver outputs No 3rd gain setting for CCU12, 14 • O-link gain remains fixed at ~3, series resistor values at input changed

  17. Lab measurement (gain) • Analogue link transfer characteristics (Note - no attenuation at input)

  18. dynamic range measurements • Dynamic range defined as number of MIPs in 512 ADC counts • Here, 1MIP assumed to be 50mA into TRI card • this estimate close to spy channel Landau average

  19. System dynamic ranges tested <Go-link #1>=2.2 <Go-link #2>=1.6 Vin FED (mV) Nominal Go-link =2.5-4.0 1500 GCu-link=1 1000 <Go-link #3>=0.95 500 0 signal (MIPs) 0 2 4 6 8 10 12 • dynamic ranges tested in X5: • approximately ±2.5MIPs, ± 4MIPs, ± 6MIPs

  20. Optical link noise • link contribution to noise in system measured Preliminary result: assumes 1MIP = 50mA from APV = 120mV from TRI • link noise as expected (close to lab measurements of links alone) • large noise value simply due to high link gain (G o-link~2.5-4.0) • gains will be better matched in final system (G o-link=1)

  21. Effect of link gain on noise contribution • Larger gain gives proportionally more noise Vout(V) s(mV) High link gain compensated in X5 by adding potential divider R=200W Þ G~1 d. range ~ 12MIPs 3.0 Go-link =3 6 Go-link =3 4 2.0 Go-link=1 2 1.0 Go-link=1 0 0 0 500 1000 0 500 1000 Vin-link(mV) Vin-link(mV) • In X5, we attenuated input signal to link to obtain large dynamic range • However, link noise not attenuated ! (factor 2.5-4.0 greater than final system)

  22. Normalized link noise • rms noise measured with scope at link output • Normalization according to usual lab procedure • rms divided by signal output for 800mV input amplitude • results close to lab values Þ good link installation

  23. Lab measurement (noise) • Analogue link noise (lab measurement, normalized to peak signal) CCU10 CCU14 CCU12 CCU11

  24. Summary • Successful integration of optical links in X5 • 16 (+4) analogue optical links installed • close to final components in most cases • various readout chain gains tested (o-link gain ~3) • from 5 to 12MIP dynamic range available • 12MIP range similar to final system • noise contribution 400-1200e for 5-12MIP range • should be close to 500e in final system with 12MIP range • 2x2 bi-directional digital 40MHz links integrated • effect of bit-errors to be investigated in lab

  25. Lab measurement (linearity) • Analogue link linearity characteristics

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