Fast Electronics for Future Experiments Gary S. Varner University - PowerPoint PPT Presentation

Fast Electronics for Future Experiments Gary S. Varner University of Hawai’i University of Hawai i Joint CPAD and IFCM, Jan. 11, 2013

Overview • Further advances at the Discovery Frontier – Depends upon developing new instruments and techniques – Exploit commodity resources • The “easy” experiments are being completed y p g p – Can’t necessarily scale up ($$$, T>N*t gradstudent ) – Innovation fuels new opportunities Innovation fuels new opportunities • What I hope to convey: 1. A new “Giga” Era implies fast timing naturally 1 A “Gi ” E i li f t ti i t ll 2. Introduce key elements 3. An example where this has been fundamentally enabling 3 A l h hi h b f d ll bli 4. A notion toward future directions 2

Detector Instrumentation Evolution History • Traditional “crate based” electronics Q-ADC – Gated Analog-to-Digital Converters Det chan TDC TDC – Referenced “triggered” Time-to-Digital Converters Disc. Trigger • High-rate applications – “pipelined operation” – Low-speed, low-resolution sampling • High channel counts – Motivation to reduce cabling – Integrate electronics onto detector elements Det chan FADC Issues: cost, power, resolution, data volume 3

A “Giga” Overview (Modern Readout) 2. 100’s of Giga flops per 4. Commodity Servers Field-Programmable running at Giga -Hz rates, Gate Array Gate Array 1000’s of Giga flops 1000’ f Gi fl Physical Physical Measurement 1. Giga sample/s “digital oscilloscope 3. Inexpensive Giga -bit/s on a chip” fiber link interconnect; Giga -bit ethernet Technology advances  high rate, high-precision experiments 4

Focus on the first of these 2. 100’s of Gigaflops per 4. Commodity Servers Field-Programmable running at Giga-Hz rates, Gate Array Gate Array 1000 s of Gigaflops 1000’s of Gigaflops Physical Physical Measurement 1. Gigasample/s “digital oscilloscope 3. Inexpensive Giga-bit/s on a chip” fiber link interconnect; Giga-bit ethernet • Defines limit of the physical measurement • What Instrumentation Physicists contribute 5

Underlying Technology • Track and Hold (T/ H) T/H Sampled Data Analog Input g p C • Pipelined storage = array of T/ H elements, with output buffering l t ith t t b ff i Top Read Bus Vout=A / (1+A) * Q/Cs Write Bus N capacitors =V1 * A/(1+A) Bottom Read Bottom Read v V1=V V1=V 2 BUS Q=Cs.V 1 4 1 Cs 3 Return Bus N caps 6

7 Tiny charge: 1mV ~ 100e - Switched Capacitor Array Sampling 20fF Channel 2 Channel 1 switches closed @ once tc es c osed @ o ce Write pointer is ~few s • Few 100ps delay Input Input

Basic Functional components On or off- chip ADC chip ADC Single storage Ch Channel l Sample timing S l ti i Control Few mm x Few mm in size Readout Control 8

The Giga Package • 2 GSa/s, 1GHz ABW T k Tektronics Scope i S • 2.56 GSa/s LAB WFS ASIC Commercial S Sampling li 0.1-6 GSa/s 2 GSa/s speed “oscilloscope on Bits/ENOBs 16/9-13+ 8/7.4 a chip” Power/Chan. < = 0.05W Few W Cost/Ch. < $10 (vol) > 100$ 9

10 Very broad Impact LAPPD  LAPPD  Fundamental enabling technology (smallest to largest) Neutrinos AMBER

To be explicit, a demanding Application ~320ps Measured Measured ~7m • RF Transient (impulsive) Events (200-1200 MHz) • 324 chan. @ 2.6GSa/s 32 h @ 2 6GS / • Completely solar powered (tight demands on power, (tight demands on po e few hundred W total) • • Need full waveforms Need full waveforms A t Antarctic Impulsive Transient Antenna ti I l i T i t A t (ANITA-I) 11

ANITA concept Typical balloon field of regard 12 ~4km deep ice! Ice RF Effective “telescope” aperture: p p clarity: clarity: • ~250 km 3 sr @ 10 18 eV ~1.2km(!) • ~10 4 @ km 3 sr 10 19 eV attenuation ( compare to ~1 km 3 at lower E) ( length 12

Large Analog Bandwidth Recorder and Digitizer with Ordered Readout [LABRADOR] ith O d d R d t [LABRADOR] • Common STOP acquisition • 3.2 x 2.9 mm Straight • Conversion in Shot 120  s (all RF inputs 2340 samples) • Data transfer takes 80  s • Ready for next • Switched 8+1 chan. * 256+4 samples event in Capacitor 200  s Array (SCA) • Massively parallel Wilkinson ADC array Random access: 13

LABRADOR performance 12-bit ADC 2.6GSa/s 1.3mV • 10 real bits (1.3V/1.3mV noise) • Excellent linearity, noise • Sampling rates up to 4 GSa/s with voltage overdrive 14

(SURF = Sampling Unit for RF) (TURF = Trigger Unit for RF) SURFv3 Board SURFv3 Board J4 to TURF J1 to CPU LAB3 RF Inputs Programming/ Monitor Header Monitor Header Trigger Inputs PCI bus: 64bits, 66MHz ~ 0.5 GigaByte/s (upgrading for 3 rd flight) 15

Logical segmentation (example Trigger Type = 1 shown) A “high rate” Experiment g p Top cluster L2 = 2 of 5 Phi = 0 (1 of 16) Raw Signals Bottom cluster L2 = 2 of 5 L2 = 2 of 5 Nadir cluster L2 = 2 of 3 Level-2 Level-1 Level-3 SS Prioritizer Prioritizer n TDRS Cluster Antenna (+compress) Phi ents/min 2-of-2 2 f 2 2-of-5 2 f 5 3-of-8 f Few eve Few kHz 5-10Hz @ 36kBy/evt @ 36kBy/evt = 36-72Mby/s = 180-360kBy/s F To disk T di k 100-200kHz 100 200kH @ 36kBy/evt 80 RF channels = 3.6-7.2Gby/s @ 1.5By * 2.6GSa/s = 312 Gbytes/s Permits thermal noise level operation 16

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The “no free lunch” Theorem • Excellent results obtained 1. Made the ANITA project possible & highly successful 2. Similar architectures being studied for new and upgraded experiments 3. Minimize costs for large systems • Not a magic solution – Significant constraints – Technology in its infancy – will continue to improve • Limits and future directions The technology in a bit more detail The technology, in a bit more detail 18

Constraint 0: An Intrinsic Limitation No power (performance savings) for continuous digitization g Won’t displace Flash ADCs “d “down conversion” i ”  For most “triggered” ‘event’ applications, not a serious drawback 19

Constraint 1: Analog Bandwidth Difficult to couple in Large BW (C is deadly) inside ASIC inside ASIC RFamp RFamp Z S Z S Vsig Vsig Vin Vin 50 C in Ω Z T f 3dB = 1/2  ZC 20

Bandwidth Limitations (LAB1 example) f 3dB = 1/2  ZC Would like smallest possible Cstore • • For 1 2GHz C < ~ 2pF (NB input protection diode ~ 10pF) For 1.2GHz, C < ~ 2pF (NB input protection diode ~ 10pF) • Minimize C, (C drain not negligible x260) 21

An Example Bandwidth Evaluation LAB3 LAB3 Transient 9 channels of 9 channels of Impulse 256 samples To do FFT better, Difference f 3dB ~> 1.2GHz reduce input and Frequency [GHz] storage C storage C 22

23 Constraint 2: kTC Noise Want small storage C, but…

Similar Constraint 2b: Leakage Current Increase C or reduce conversion time << 1mV Sample channel-channel variation Sample channel-channel variation ~ fA leakage typically 24

Constraint 3: Digitization • No missing codes • Linearity as good as 12-bit ADC can make ramp • Can bracket range of interest Run count during ramp Wilki Wilkinson ADC ADC • Excellent linearity • Basically as good as can make current source/comparator • Comparator ~ 0.4 – 2.1V; 133MHz GCC max (~ 31us) 25

Constraint 4: Sample Aperture Variance • Inverter chain has transistor variations i ti •   t i between samples differ  “Fixed pattern aperture jitter” • “Differential temporal nonlinearity” TD i =  t i –  t nominal i i nominal • “Integral temporal nonlinearity” TI i =  t i – i  t nominal • “Random aperture jitter” = variation of  t i between measurements i  t 1  t 2  t 3  t 4  t 5 TD TD 1 TI TI 5 26

Non-uniform sampling timebase SURF data SURF data Long-suffering ANITA collaborator Long suffering ANITA collaborator 27

28 10-15% of dT typical dT Spread 2.6 GSa/s [LABRADOR3]

Average aperture calibration • Fixed aperature offsets are Fixed aperature offsets are constant over time, can be measured and corrected • Several methods are commonly used (sine fit [left], zero-crossing) • Most use sine wave with random phase and correct for TD i on a statistical basis l b 29

Sine Curve Fit Method i  500 1024 2           2 2 ( ( sin( ) )) min y a i o ji j j i j f   j j 0 i 0 j j y ji : i-th sample of measurement j a j f j  j o j : sine wave parameters j j j j  i : phase error  fixed jitter “Iterative global fit”: Iterative global fit : • Determine rough sine wave parameters fo each meas for each measurement by fit ement b fit • Determine  i using all measurements where sample “i” is near zero crossing • Make several iterations j S. Lehner, B. Keil, PSI 30

Option 1: Even Faster Sampling p p g 6 GSPS * 8 = 48 GSPS ) 8 = 25ps) (200ps/8 delays Possible with delay is implemented on PCB o b d ay p d o 31

32 Coupling between wire-bonds, Vref Constraint 5: Cross-talk