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Paul Scherrer Institute
Stefan Ritt The PSI DRS4 Integrated Circuit Chip
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Agenda Introduction to Switched Capacitor Array Chips
Comparison with FADCs Overview of chips on the market The DRS4 chip Design principles Special features Some applications New ideas for DRS5 chip to be designed in 2011 Increased bandwidth Zero dead time DPP Workshop PSI March 15th, 2011
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Introduction to Switched Capacitor Array Chips
DPP Workshop PSI March 15th, 2011
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Detectors in Particle Physics
Particles interact with matter and produce light: Signal: ~ 100’s mV ns DPP Workshop PSI March 15th, 2011
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Flash ADC Technique FADC Q-sensitive Preamplifier Baseline Restoration PMT/APD Wire Shaper 60 MHz 12 bit Amplitude TDC Time “Fast” 12 bit Transimpedance Preamplifier FADC PMT/APD Wire Digital Processing Shaper is used to optimize signals for “slow” 60 MHz FADC Shaping stage can only remove information from the signal Shaping is unnecessary if FADC is “fast” enough All operations (CFD, optimal filtering, integration) can be done digitally DPP Workshop PSI March 15th, 2011
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Nyquist-Shannon Theorem
If a function x(t) contains no frequencies higher than F Hertz, it is completely determined by giving its ordinates at a series of points spaced 1/(2F) seconds apart. If a detector produces frequencies up to 500 MHz (0.6 ns rise time), all information from that detector is recorded if sampled at 1 GSPS with good enough signal-to-noise ratio DPP Workshop PSI March 15th, 2011
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How to measure best timing?
Simulation of MCP with realistic noise and different discriminators K. Byrum, H. Frisch, J.-F. Genat et al., IEEE Trans.Nucl.Sci.57, 525 (2010) DPP Workshop PSI March 15th, 2011
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Currently available fast ADCs
8 bits – 3 GS/s – 1.9 W 24 Gbits/s 10 bits – 3 GS/s – 3.6 W 30 Gbits/s 12 bits – 3.6 GS/s – 3.9 W 43.2 Gbits/s 14 bits – 0.4 GS/s – 2.5 W 5.6 Gbits/s 24x1.8 Gbits/s Requires high-end FPGA Complex board design FPGA power 1.8 GHz! DPP Workshop PSI March 15th, 2011
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ADC boards 1-10 k€ / channel PX1500-4: 2 Channel 3 GS/s 8 bits
ADC12D1X00RB: 1 Channel 1.8 GS/s 12 bits 1-10 k€ / channel DPP Workshop PSI March 15th, 2011
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Switched Capacitor Array
0.2-2 ns Inverter “Domino” ring chain IN Waveform stored Out FADC 33 MHz Clock Shift Register “Time stretcher” GHz MHz DPP Workshop PSI March 15th, 2011
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Switched Capacitor Array
Cons No continuous acquisition Limited sampling depth Nonlinear timing Pros High speed (5 GHz) high resolution (11.5 bit) High channel density (9 channels on 5x5 mm2) Low power (10-40 mW / channel) Low cost (~ 10€ / channel) Dt Dt Dt Dt Dt Goal: Minimize Limitations STRAW3 TARGET LABRADOR3 G. Varner Univ. of Hawaii AFTER MATACQ SAM D. Breton E. Delagnes CEA Saclay DRS1 DRS2 DRS3 DRS4 This talk DPP Workshop PSI March 15th, 2011
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The DRS4 Chip DPP Workshop PSI March 15th, 2011
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Design Options CMOS process (typically 0.35 … 0.13 mm) sampling speed Number of channels, sampling depth, differential input PLL for frequency stabilization Input buffer or passive input Analog output or (Wilkinson) ADC Internal trigger Exact design of sampling cell PLL Trigger ADC DPP Workshop PSI March 15th, 2011
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DRS History 1995 2002 2004 2007 2008 DSC DRS1 DRS2 DRS3 DRS4
Roger Schnyder, Christian Brönnimann, pb Tiny signal 0.2 pF 20 pF DRS1 2002 I Temperature Dependence ~kT 2004 DRS2 Roberto Dinapoli DRS3 2007 2008 DRS4 PLL-regulated Sampling Speed DPP Workshop PSI March 15th, 2011
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DRS4 Fabricated in 0.25 mm 1P5M MMC process (UMC), 5 x 5 mm2, radiation hard 8+1 ch. each 1024 bins, 4 ch. 2048, …, 1 ch. 8192 Passive differential inputs/outputs Sampling speed 700 MHz … 5 GHz On-chip PLL stabilization Readout speed 30 MHz, multiplexed or in parallel DPP Workshop PSI March 15th, 2011
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12 bit resolution 11.5 bits effective resolution
DPP Workshop PSI March 15th, 2011
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Bandwidth Bandwidth is determined by bond wire and internal bus resistance/capacitance: 850 MHz (QFP), 950 MHz (QFN), ??? (flip-chip) ~2 nH Bond wire Parasitic ~10 pF final bus width QFP package 850 MHz (-3dB) Measurement Simulation Ueli Hartmann DPP Workshop PSI March 15th, 2011
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Bump Bonding Reduce input inductance by using
bump bonding instead of wire bonding 200 mm 75 mm DPP Workshop PSI March 15th, 2011
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How to minimize dead time ?
Fast analog readout: 30 ns / sample Parallel readout Region-of-interest readout Simultaneous write / read AD9222 12 bit 8 channels DPP Workshop PSI March 15th, 2011
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ROI readout mode e.g. 100 samples @ 33 MHz 3 us dead time
delayed trigger stop normal trigger stop after latency Trigger stop Delay 33 MHz e.g MHz 3 us dead time 300,000 events / sec. readout shift register Patent pending! DPP Workshop PSI March 15th, 2011
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Daisy-chaining of channels
Domino Wave Domino Wave clock clock 1 enable input Channel 0 enable input Channel 0 enable input Channel 1 1 enable input Channel 1 1 Channel 2 Channel 2 Channel 3 1 Channel 3 1 Channel 4 Channel 4 Channel 5 1 Channel 5 1 Channel 6 Channel 6 Channel 7 1 Channel 7 DRS4 can be partitioned in: 8x1024, 4x2048, 2x4096, 1x8192 cells Chip daisy-chaining possible to reach virtually unlimited sampling depth DPP Workshop PSI March 15th, 2011
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Simultaneous Write/Read
FPGA Channel 0 readout 1 Channel 0 Channel 0 Channel 1 Channel 1 1 Channel 1 8-fold analog multi-event buffer Channel 2 1 Channel 2 Channel 3 Channel 4 Channel 5 Channel 6 Channel 7 Expected crosstalk ~few mV DPP Workshop PSI March 15th, 2011
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DRS4 around the world Shipped (-Jan 2011): 2200 Chips
120 Evaluation Boards DPP Workshop PSI March 15th, 2011
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MEG Experiment MEG experiment @ PSI searches for meg decay
After ~10 years of chip design, DAQ setup, firmware programming, MEG runs with 3000 channels as designed 40 ps timing resolutions between all channels, running at 1.6 GS/s “Double buffer” readout mode increases life time to 99.7 % at 10 Hz event rate (3 MB/event) Took 400 TB in 2010 DPP Workshop PSI March 15th, 2011
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DRS4 @ MEG 3000 Channels LMK03000 4 x DRS4 32 channels
DPP Workshop PSI March 15th, 2011
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On-line waveform display
PMTs “virtual oscilloscope” template fit click pedestal histo DPP Workshop PSI March 15th, 2011
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Crosstalk elimination
Crosstalk removal by subtracting empty channel subtract Hit Hit DPP Workshop PSI March 15th, 2011
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Template Fit pb Experiment 500 MHz sampling Determine “standard” PMT pulse by averaging over many events “Template” Find hit in waveform Shift (“TDC”) and scale (“ADC”) template to hit Minimize c2 Compare fit with waveform Repeat if above threshold Store ADC & TDC values DPP Workshop PSI March 15th, 2011
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Trigger and DAQ on same board
SCA can only sample a limited (1024-bin window) many application require a wider window, trigger capability would require continuous digitization Using a multiplexer in DRS4, input signals can simultaneously digitized at 120 MHz and sampled in the DRS FPGA can make local trigger (or global one) and stop DRS upon a trigger DRS readout (5 GSPS) though same 8-channel FADCs DRS4 global trigger bus trigger FPGA MUX DRS FADC 12 bit 65 MHz analog front end LVDS SRAM DPP Workshop PSI March 15th, 2011
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“Slow” waveform and “Fast” window
Triggered DRS Waveform 1 GSPS (1 ns bins) up to 5 GSPS Window only limited by RAM Continuous Waveform 120 MSPS (8 ns bins) DPP Workshop PSI March 15th, 2011
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Sine Curve Fit Method yji : i-th sample of measurement j
aj fj aj oj : sine wave parameters bi : phase error fixed jitter “Iterative global fit”: Determine rough sine wave parameters for each measurement by fit Determine bi using all measurements where sample “i” is near zero crossing Make several iterations j S. Lehner, B. Keil, PSI DPP Workshop PSI March 15th, 2011
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Fixed Pattern Jitter Results
TDi typically ~50 ps 5 GHz TIi goes up to ~600 ps Jitter is mostly constant over time, measured and corrected Residual random jitter 3-4 ps RMS Achievable resolution exceeds best CFD + HPTDC DPP Workshop PSI March 15th, 2011
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Time-of-Flight PET Conventional electronics: CFD – TDC: 500 ps RMS
TOF needs: ps >1 MHz rate C. Levin, Stanford University DPP Workshop PSI March 15th, 2011
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ToF-PET Project “Ping-Pong Scheme” 20 samples (10 ns @ 2 GS/s)
Started fall 2010 after NSS/MIC in Knoxville (Siemens PET R&D home) New project started to replace current PET electronics with DRS4 (5) PCB ready summer 2011, firmware by Univ. Tübingen Simulations show that SCA technique can achieve 100 ps easily FPGA “Ping-Pong Scheme” 1 Channel 0 Channel 0 Channel 1 Channel 1 ROI Channel 2 20 samples (10 2 GS/s) * 30 ns / sample = 600 ns + 40 ns overhead = 640 ns 1 MHz rate Channel 3 Channel 4 Channel 5 Channel 6 Channel 7 DPP Workshop PSI March 15th, 2011
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DRS5 Chip Ideas DPP Workshop PSI March 15th, 2011
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Plans for DRS5 mSR CTA Increase analog bandwidth ~5 GHz
Smaller input capacitance Increase sampling speed ~10 GS/s Switch to 110 nm technology Deeper sampling depth 8 x 4096 / chip Minimize readout time (“dead time free”) for muSR & ToF-PET (minor) reduction in analog readout speed (30 ns 20 ns) Implement FIFO technology J. Milnes, J. Howoth, Photek mSR ~MHz event rate CTA DPP Workshop PSI March 15th, 2011
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How to combine best of both worlds? Next Generation SCA
Short sampling depth Deep sampling depth Low parasitic input capacitance High bandwidth Large area low resistance bus, low resistance analog switches high bandwidth Digitize long waveforms Accommodate long trigger delay Faster sampling speed for a given trigger latency How to combine best of both worlds? DPP Workshop PSI March 15th, 2011
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Cascaded Switched Capacitor Arrays
input shift register 32 fast sampling cells (10 GSPS/110nm CMOS) 100 ps sample time, 3.1 ns hold time Hold time long enough to transfer voltage to secondary sampling stage with moderately fast buffer (300 MHz) Shift register gets clocked by inverter chain from fast sampling stage fast sampling stage secondary sampling stage DPP Workshop PSI March 15th, 2011
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How noise affects timing
voltage noise band of signal voltage noise Du signal height U timing jitter arising from voltage noise timing uncertainty Dt rise time tr timing jitter is much smaller for faster rise-time number of samples on slope DPP Workshop PSI March 15th, 2011
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TDC vs. Waveform Digitizing
Constant Fraction Discriminator Q-sensitive Preamplifier PMT/APD Wire Shaper TDC CFD and TDC on same board crosstalk CFD depends on noise on single point, while waveform digitizing can average over several points Inverter chain is same both in TDCs and SCAs Can we replace TDCs by SCAs? yes if the readout rate is sufficient DPP Workshop PSI March 15th, 2011
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Typical Waveform Only short segments of waveform need high speed readout DPP Workshop PSI March 15th, 2011
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Dead-time free acquisition
Self-trigger writing of short 32-bin segments Simultaneous reading of segments Quasi dead time-free Data driven readout Ext. ADC runs continuously ASIC tells FPGA when there is new data Coarse timing from 300 MHz counter Fine timing by waveform digitizing and analysis in FPGA 20 * 20 ns = 0.4 ms readout time 2 MHz sustained event rate Attractive replacement for CFD+TDC DRS5 DPP Workshop PSI March 15th, 2011
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Plug & Play Firmware Emphasis shift from dedicated hardware to firmware Pre-designed modules for CFD, TDC, peak sensing ADC, … Modules can be configured by user and downloaded CFD TDC FIFO ADC Readout SCALER Interface FIFO FIFO ADC FIFO Data bus Parameter bus DPP Workshop PSI March 15th, 2011
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Conclusions DRS4 chip successfully used in many areas, true potential of SCA technology is just now discovered Planned DRS5 chip will increase BW and decrease readout dead time SCA technology should be able to replace most traditional electronics in particle detection DPP Workshop PSI March 15th, 2011
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Thanks to … Roland Horisberger: Original Idea
Roberto Dinapoli: Analog Design of DRS3+4 Ueli Hartmann: DRS4 Evaluation Boards PSI chip design core team DPP Workshop PSI March 15th, 2011
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