1. D.Breton, E.Delagnes, J.Maalmi, J.Va’vra – LNF SuperB Workshop– December 2009 Picosecond time measurement using ultra fast analog memories: new results since SLAC workshop. D.Breton & J.Maalmi (LAL Orsay), E.Delagnes (CEA/IRFU), J.Va’Vra (SLAC)

2. D.Breton, E.Delagnes, J.Maalmi, J.Va’vra – LNF SuperB Workshop– December 2009 The USB_WaveCatcher board SAM Chip Dual 12-bit ADC 1.5 GHz BW amplifier. µ USB Reference clock: 200MHz => 3.2GS/s 2 analog inputs. DC Coupled. Trigger discriminators Trigger input Pulsers for reflectometry applications Board has to be USB powered => power consumption < 2.5W Trigger output Cyclone FPGA +5V Jack plug The goal here is to measure the board’s capacity to perform the measurement of the time difference between two pulses (like a TDC but directly with analog pulses !).

3. D.Breton, E.Delagnes, J.Maalmi, J.Va’vra – LNF SuperB Workshop– December 2009 OSC (200MHz) SAM CPT1 Div/N CPT2 Div/M Sync_reset USB interface (~ 20MHz) ADC clock (~ 10MHz) FPGA Div Block diagram of clock distribution on the board Fe=3.2GHz Clean power supply N = 11 M = 21

4. D.Breton, E.Delagnes, J.Maalmi, J.Va’vra – LNF SuperB Workshop– December 2009 Mismatches of elements in the delay chain induce: => dispersion of delay duration => error on the sampling time. Fixed for a given tap => “Fixed Pattern Aperture Jitter” Dispersion of single delays => time DNL. Cumulative effect => time INL. Gets worse with delay line length. Systematic effect => non equidistant samples (bad for FFT). => correction with Lagrange polynomial interpolation. Drawbacks: computing power. => good (and easy) calibration required. Definition: Fixed Pattern Aperture Jitter Real signal Fake signal After interpolation Δt[cell]

5. D.Breton, E.Delagnes, J.Maalmi, J.Va’vra – LNF SuperB Workshop– December 2009 Extraction of fixed pattern and random jitter. Method: 135MHz-1.4Vpp sine-wave sampled by SAM Search of zero-crossing segment => length and position (cell). –Higher frequency => 320-ps segments are not straight enough –Lower frequency => more jitter because of noise Histogram of length[position]: –propor. to time step duration assuming sine = straight line (bias ~ 1ps rms). –mean_length[position] = fixed pattern effect => DNL => INL –sigma_length[position] = random effect => Random Jitter (Sinewave is 197MHz on this plot)

6. D.Breton, E.Delagnes, J.Maalmi, J.Va’vra – LNF SuperB Workshop– December 2009 Fixed pattern jitter Correction has a huge effect! DNL INL After correction 0.33ps rms 16.9ps rms 1.15ps rms 7.5 ps rms DNL INL

7. D.Breton, E.Delagnes, J.Maalmi, J.Va’vra – LNF SuperB Workshop– December 2009 Random jitter The results are very reproducible from run to run The INL correction seems to be stable over a long period of time (days at least)  can be stored in the on-board EEPROM like the cell pedestals The correction works rather well for other input frequencies between 100 and 200MHz, with a residual INL always remaining below 2.5ps. => this validates the correction method. 1.95ps rms DLL jitter Clock jitter

8. D.Breton, E.Delagnes, J.Maalmi, J.Va’vra – LNF SuperB Workshop– December 2009 Timing measurement with two pulses. Source: asynchronous pulse summed with itself reflected at the end of an open cable. Time difference between the two pulses extracted by crossing of a fixed threshold determined by polynomial interpolation of the 4 neighboring points (on 3000 events). σ Δt ~ 11ps rms => jitter for a single pulse = 8 ps ! σ = 10.9ps rms σ = 11.4ps rms Δt ~ 11ns Δt ~ 21ns Vth

9. D.Breton, E.Delagnes, J.Maalmi, J.Va’vra – LNF SuperB Workshop– December 2009 Remarks about effects of time non-linearity. Effects of time DNL and INL on time measurements might be misunderstood. When measuring the time difference between two close pulses with a an analog memory, these effects really depend on the memory structure. For instance, if one sends asynchronous pulses with a constant and short delay (a few ns), the jitter will be mainly due to the variations in the local DNL along the few consecutive cells involved in each measurement. But the effect of the local INL will be mostly masked. This means: –That jitter will depend on the distance between pulses –That it might not be right to extrapolate the single pulse jitter from the difference by dividing it by √2 without correlating it with: the effect of the memory structure the potential dispersions between different circuits in a multi-channel system the long term drift after time calibration if the latter was performed This is especially true with analog memories making use of long delay lines (and even more if they are not servo-controlled) This is much less sensitive in matrix structures where delay lines are very short, servo- controlled, and synchronized to the clock

10. D.Breton, E.Delagnes, J.Maalmi, J.Va’vra – LNF SuperB Workshop– December 2009 The Wave Catcher on Jerry’s test bench at SLAC

11. D.Breton, E.Delagnes, J.Maalmi, J.Va’vra – LNF SuperB Workshop– December 2009 Results from first data taking (5000 events) 600 raw pulses (spline interpolation between samples)

12. D.Breton, E.Delagnes, J.Maalmi, J.Va’vra – LNF SuperB Workshop– December 2009 600 pulses: zoom => xtalk<<0.5%

13. D.Breton, E.Delagnes, J.Maalmi, J.Va’vra – LNF SuperB Workshop– December 2009 600 normalized pulses superimposed Common threshold

14. D.Breton, E.Delagnes, J.Maalmi, J.Va’vra – LNF SuperB Workshop– December 2009 Sigma(Delta T) = 25 ps (linear interpolation) (no gaussian fit) Sigma (DeltaT) = 24 ps (spline interpolation) Nearly independent on fraction ratio in the 0.25-0.5 range Digital CFD time difference. Fraction ratio = 23%.

15. D.Breton, E.Delagnes, J.Maalmi, J.Va’vra – LNF SuperB Workshop– December 2009 « Average » pulse: black Average +/-2 sigma: red Used in cross-correlation algorithm. Not better than CFD… Average pulse and 2-sigma templates

16. D.Breton, E.Delagnes, J.Maalmi, J.Va’vra – LNF SuperB Workshop– December 2009 Conclusion The USB Wave Catcher has become a demonstrator for the use of matrix analog memories in the field of ps time measurement. Lab timing measurements showed a single pulse resolution of ~16 ps rms without time INL correction, and less than 10ps after correction. The board has been tested with MCPPMT’s for low-jitter light to time conversion on Jerry’s test bench. The first results are coherent with previous measurements (based both on Ortec and Target chip): 24ps for the time difference => 17ps for a single pulse More generally, tests showed us that analog memories look perfectly suited for ps time measurement. => no need for analog to digital pulse conversion, low power and low cost ! Jerry will now refine these results.

17. D.Breton, E.Delagnes, J.Maalmi, J.Va’vra – LNF SuperB Workshop– December 2009 2 DC-coupled 256-deep channels with 50-Ohm active input impedance ±1.25V dynamic Range, with full range 16-bit individual tunable offsets 2 individual pulse generators for reflectometry applications. On-board charge integration calculation. Bandwidth > 500MHz Signal/noise ratio: 11.9 bits rms (noise = 630 µV RMS) Sampling Frequency: 400MS/s to 3.2GS/s Max consumption on +5V: 0.5A Absolute time precision in a channel (typical): without INL calibration: 20ps rms (400MS/s to 1.6GS/s) 16ps rms (3.2GS/s) after INL calibration 12ps rms (400MS/s to 1.6GS/s) 8ps rms (3.2GS/s) Relative time precision between channels: still to be measured. Trigger source: software, external, internal, threshold on signals Acquisition rate (full events)Up to ~1.5 kHz over 2 full channels Acquisition rate (charge mode)Up to ~40 kHz over 2 channels Summary of the board performances. Acquisition software with graphical interface is now available