1. FED V1 Pulse Shape Issues System Meeting, CERN 14 th -16 th October 2003 M. Noy Imperial College London Pulse Shape Issues for the Tracker FED M. Noy Imperial College London System Meeting 14 th -16 th October 2003

2. FED V1 Pulse Shape Issues System Meeting, CERN 14 th -16 th October 2003 M. Noy Imperial College London System: Schematic of system architecture no. 1 Linux PC VME bus SBS 620 Optical Test CardVI2CFED Optical Fibre Clock, 40MHz, LVDS Trigger, LVDS HAL root FFv1DebugObject OptoTXObjec t FFv1Object FedTesterObject Optical link

3. FED V1 Pulse Shape Issues System Meeting, CERN 14 th -16 th October 2003 M. Noy Imperial College London Pulse shape at AD9218 inputs looks like this:

4. FED V1 Pulse Shape Issues System Meeting, CERN 14 th -16 th October 2003 M. Noy Imperial College London Source overshoot (+ something else) Source undershoot Unknown 1 Unknown 2 Result of performing a ‘timing calibration’ on a 25ns pulse

5. FED V1 Pulse Shape Issues System Meeting, CERN 14 th -16 th October 2003 M. Noy Imperial College London System: Schematic of FED “Emulator” test-bench: “scope mode” Linux PC VME bus SBS 620Optical Test CardVI2C Optical Fibre Clock 40MHz and trigger (LVDS) HAL root OptoTXObjec t Optical link Virtex II eval. board AD9218 Eval. board Opto-Rx (9001) Proto. board Level & diff conv. Single FED Channel Emulator I2C config/readout FedEmulato r Skewed clk

6. FED V1 Pulse Shape Issues System Meeting, CERN 14 th -16 th October 2003 M. Noy Imperial College London Pulse shape as measured differentially at the input to the AD9218:

7. FED V1 Pulse Shape Issues System Meeting, CERN 14 th -16 th October 2003 M. Noy Imperial College London Effect is reproducible on the AD evaluation board… PRELIMINARY

8. FED V1 Pulse Shape Issues System Meeting, CERN 14 th -16 th October 2003 M. Noy Imperial College London Fit gradient = 0.045  0.003 (65MSPS device @ 40MHz) (fit gradient ~0.04 for the 105MSPS device @ 40MHz) PRELIMINARY

9. FED V1 Pulse Shape Issues System Meeting, CERN 14 th -16 th October 2003 M. Noy Imperial College London Changing the operational mode of the AD9218 results in a large improvement of the leading edge PRELIMINARY

10. FED V1 Pulse Shape Issues System Meeting, CERN 14 th -16 th October 2003 M. Noy Imperial College London Result of same analysis run over a similar 1Vp-p data set PRELIMINARY

11. FED V1 Pulse Shape Issues System Meeting, CERN 14 th -16 th October 2003 M. Noy Imperial College London “The input sampling mechanism is different in the two modes; in 1Vpp mode a sampling cap in the input pipeline is cleared between samples as part of the track/hold process. in 2Vpp mode, this 'clearing' of the sampling cap does not occur, but is carried thru the pipeline. This indicates a potential sensitivity in 2Vpp mode for a pulse-type sampling application.” Analog Devices: For the FED: Having the AD9218 in 1Vpp mode requires a gain of 0.5 at the front end…

12. FED V1 Pulse Shape Issues System Meeting, CERN 14 th -16 th October 2003 M. Noy Imperial College London Solution 1: Halve the OptoRX load resister value Solution 2: Introduce a 100 Ohm terminator between the differential lines Both of these modifications have been made to different channels on FED Serial 001.

13. FED V1 Pulse Shape Issues System Meeting, CERN 14 th -16 th October 2003 M. Noy Imperial College London Solution 1: Noise increases by ~0.25ADC counts RMS PRELIMINARY

14. FED V1 Pulse Shape Issues System Meeting, CERN 14 th -16 th October 2003 M. Noy Imperial College London Solution 2: Noise level comparable to before the modification PRELIMINARY

15. FED V1 Pulse Shape Issues System Meeting, CERN 14 th -16 th October 2003 M. Noy Imperial College London Summary AD (the support engineer) shows a continued interest in understanding the effect. Pre-undershoot seems to be intrinsic to the device in the 2Vp-p mode, at a 5% level Have solution that require slight modifications to the FE of the FED Solution 1: requires changing opto-rx load Small increase in noise Possible settling issues (doesn’t look serious). Solution 2: Requires the introduction of a new resistor, and hence a change in the FED FE schematics/layout Possibility of 3 rd solution from Analog Devices/some 3 rd party

16. FED V1 Pulse Shape Issues System Meeting, CERN 14 th -16 th October 2003 M. Noy Imperial College London Future: Continue to take data to characterise the FE in the new mode of operation  Determine which solution is the most suitable Maintain communication with AD to improve understanding of device Look into the other pulse shape issues