CMS FED Testing Update M. Noy & J. Leaver Imperial College Silicon Group

CMS FED Testing Currently: SEQSI LVDS LVTTL DAC Evaluation board UTP Opto- Tx Optical Fibre Opto- Rx I2C master I2C control Coax 8 bit oscilloscope GPIB VME PC LVDS  LVTTL Line driver + (optional) level shift Network I2C slave

CMS FED Testing Picture of the DAC evaluation board DAC Line driver UTP out LVTTL data in, from level converter

CMS FED Testing Picture of the key link components Opto-Tx Opto-Rx I2C cable Single ended output to scope UTP from DAC/line driver Optical fibre

CMS FED Testing DAC scope UTP V out Opto-Tx DAC Evaluation Board Line driver Opto-Rx

CMS FED Testing Signal before the link  200mV (V + -V - =400mV ) differential signal with no offset. higher bandwidth  ringing and faster rise/fall time. Time scale is relative to the scope trigger point on all plots.

CMS FED Testing Signal after the link Single ended, with offset. No ringing but slower rise/fall times

CMS FED Testing Signal noise/jitter after the link Note:no scale on the width of the line. This is an impression of the infinite persistence scope trace => spread unknown. (Measurements are real).

CMS FED Testing Rise time, 10% to 90% of full scale.

CMS FED Testing Fall time 90% to 10% of full scale

CMS FED Testing Linearity: link is being operated in the linear region of the Tx/Rx Settings: x0, x1, x2, x3, x4, x5=0,0,0,0,1 (recommended by CERN)

CMS FED Testing Sample APV25 pair of multiplexed frames with simulated 1 MIP signal

CMS FED Testing Multiplexed APV25 header with zero pipeline address 6 start bits pipeline address (16 bits) 2 error bits 2x12x25ns bits =

CMS FED Testing Zoom in of the 1 MIP signal upon its pedestal Approx: Pedestal value here is 509 lsbs, 4096 levels in 405mV  0.099mV/lsb 1 MIP  4096/8=512 lsbs  Total signal =570+(405/4096)*( ) = *1021=671mV

We attached a heating element and a thermocouple to the laser package and used the following PID equation to stabilise the temperature through a feedback loop. W = P [ (T s - T 0 ) + D d (T s - T 0 ) /dt + I  (T s - T 0 )dt] The temperature was varied between 30ºC and 40ºC in ~1ºC steps. The output of the Rx was recorded after a stabilisation time, for some measurement time. CMS FED Testing Temperature Control

Laser threshold bias current behaves like I th =I 0 exp(T/T 0 ) Which implies  I th  I th  T/T 0 And (after a few lines and other things!)  V out  -R eff G  Rx  l I th  T/T 0 Typical parameter values yield an expected 34.1°C)  V out /  T  mV/°C CMS FED Testing Temperature Measurements

CMS FED Testing Temperature Measurement Results Approximated with a linear fit V=mT+C Where m = -(89.8  1.8) mV/°C and C = (4137  62) mV Good agreement with expected value (of 90.8mV/°C), but some of the parameters are loosely defined

Temperature stabilisation is good, with random fluctuations of the order  0.02°C. There is some unknown systematic error, that does not exceed  0.44°C. Have statistics of 150x500 voltage points and 150 temperature points per temperature setting. Statistical errors are too small to account for the largest random deviation, probably spurious. We could repeat the whole measurement again using smaller T steps, but probably won’t due to time constraints. CMS FED Testing Temperature Measurement Errors

CMS FED Testing Summary Have a complete working single fibre, possible to drive 4 with identical signals using the current Opto-Tx. Possible to obtain a further 2 of the 4 channel prototypes from CERN  complete 12 channels could in principle be driven with identical signals. Dependence of laser operation on temperature is now better understood, and fine temperature control is possible. We feel confident that a system such as the one we have will allow sufficient temperature stability for the fed testing needs. Work is in progress to produce an application specific version of the SEQSI simpler operation longer RAM pipeline clean/synchronous stop from VME possible stepping through

Future Work Have 1 (untested) Opto-Rx emulator to drive the analogue stage of the FED directly over copper (I.e. eliminating the optical link) Verify DAC Linearity: Summer student(?) More thought into a test vectors and their comparison with the FED output CMS FED Testing