Progress on signal processing techniques for Lumical ... · sources – laser, 90Sr source,...

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Progress on signal processing techniques for Lumical testbeam and CLIC detectors Szymon Kulis, Marek Idzik Faculty of Physics and Applied Computer Science AGH University of Science and Technology Predeal, Romania | FCAL Collaboration Workshop 30.V - 01.VI.2011

Transcript of Progress on signal processing techniques for Lumical ... · sources – laser, 90Sr source,...

Page 1: Progress on signal processing techniques for Lumical ... · sources – laser, 90Sr source, generator • Good qualitative agreement for results obtained with different sources •

Progress on signal processing techniques for

Lumical testbeam and CLIC detectors

Szymon Kulis, Marek Idzik

Faculty of Physics and Applied Computer Science

AGH University of Science and Technology

Predeal, Romania | FCAL Collaboration Workshop 30.V - 01.VI.2011

Page 2: Progress on signal processing techniques for Lumical ... · sources – laser, 90Sr source, generator • Good qualitative agreement for results obtained with different sources •

Agenda

• Motivation & Goals

• Deconvolution principle

● Experimental & MC setup

● Preliminary Measurement & MC results

• Gated integrator concept

• Summary & Future plans

Page 3: Progress on signal processing techniques for Lumical ... · sources – laser, 90Sr source, generator • Good qualitative agreement for results obtained with different sources •

Motivation

• During next FCAL testbeam we will have to use technique which allows us to reconstruct amplitude (and maybe time) based on relatively rare samples (asynchronous sampling)

• In CLIC– Bunch crossing separation ~ 0.5 ns– No external event trigger will be available

• Detector subsystems will need triggerless readout electronics fulfilling a number of requirements:– Precise time information

– Good amplitude resolution

– Good pileup rejection

– Low power consumption

Page 4: Progress on signal processing techniques for Lumical ... · sources – laser, 90Sr source, generator • Good qualitative agreement for results obtained with different sources •

Readout electronics diagram - deconvolution

• Pulse at output of shaper v(t) is convolution of input signal (current from sensor – s(t) ) and impulse response of readout chain h(t):

• Using data from continuously running ADC and taking advantage of known pulse shape one can perform invert procedure – deconvolution – to get information about event time and amplitude

v t =∫−∞

h t−x s x dx

Page 5: Progress on signal processing techniques for Lumical ... · sources – laser, 90Sr source, generator • Good qualitative agreement for results obtained with different sources •

Deconvolution for CR-RC shaping

• Only two multiplications and three additions (very fast and light !)

• Deconvolution produces non-zero data only when one or two first samples are on baseline,and second/third is on pulse

• Initial time of pulse is found from ratio of those samples

• Amplitude is found from sum of those samples, multiplied by time dependent correction factor

• Deconvolution reduces (infinite number) of CR-RC pulse samples to 1 or 2 non zero samples !

Look Up Tables used

Can be done off-line

CR-RC, Tsmp

=Tpeak

=1, amp =1

}

d i=siw1 si−1w2 s i−2

Page 6: Progress on signal processing techniques for Lumical ... · sources – laser, 90Sr source, generator • Good qualitative agreement for results obtained with different sources •

CR-RC Deconvolution properties | Pileup

• Two events can be separated and precisely measured if they are distant 2-3 T

smp

• For shorter distance between pulses additional signature of not resolvable pileup may be used (more than 2 non zero samples)

CR-RC, Tsmp

=Tpeak

=1, amp =1

Page 7: Progress on signal processing techniques for Lumical ... · sources – laser, 90Sr source, generator • Good qualitative agreement for results obtained with different sources •

Measurement Setup configuration

Signal source:

• Pulse generator (AGILENT 81150A)

– Signal : Current pulse

– Trigger : second channel (channel to channel jitter < 100ps)

• Radioactive source 90Sr

– Signal : β- ~546 keV

– Trigger : Scintillator + PMT (poor time resolution >~ 1ns)

• Laser (PDL 800-D)

– Signal : Infrared photons 1060nm

– Trigger : provided by device(excellent time resolution, jitter < 100ps)

• MSO7104B 4Gsps (250ps) Digital sampling oscilloscope used as ADC

New prototype with Multichannel ADC SoC

ASIC is almost ready

Page 8: Progress on signal processing techniques for Lumical ... · sources – laser, 90Sr source, generator • Good qualitative agreement for results obtained with different sources •

Photograph of Measurement Setup

MSO7104Bsampling oscilloscope

E3612Apower supply

81150Apulse generator

Sensor & FE BOXScintillator & photomultiplier

Keithley 237HV Supply

Laser Head

PicoQuantPDL 800D

Radioactive source

Page 9: Progress on signal processing techniques for Lumical ... · sources – laser, 90Sr source, generator • Good qualitative agreement for results obtained with different sources •

Monte Carlo Software architecture

object oriented library written in Python

A dedicated software was developed to reproduce all measurements in order to compare deconvoluted experimental results with MC simulations results

Page 10: Progress on signal processing techniques for Lumical ... · sources – laser, 90Sr source, generator • Good qualitative agreement for results obtained with different sources •

Linearity check – measurements with laser

• Deconvolution algorithm is linear (as expected)

• For small SNR (<10) reconstructed amplitude is not yet optimised

• NF is slightly above 0, almost no degradation of SNR

• MC fits well to measurements

Tpeak

= Tsmp

= 60ns

NF=20 log10 SNRin

SNRout

Page 11: Progress on signal processing techniques for Lumical ... · sources – laser, 90Sr source, generator • Good qualitative agreement for results obtained with different sources •

Time reconstruction – measurements with laser

• Reconstructed time doesn't depend on amplitude (as expected)

• For Tpeak

= Tsmp

= 60ns time resolution in range 2-7 ns is obtained

• MC fits well to measurements

Constant Trigger delay

Tpeak

= Tsmp

= 60ns

Page 12: Progress on signal processing techniques for Lumical ... · sources – laser, 90Sr source, generator • Good qualitative agreement for results obtained with different sources •

Deconvolution as a function of Sampling Period Laser pulses, SNR ~20, T

peak = 60ns

• For Tsmp

between 20-40 ns time

resolution between 1-2 ns can be obtain for SNR 20 and T

peak = 60 ns

• Tsmp

should be a compromise between

power consumption (ADC) and requested timing resolution

• Wide plateau (30-70ns) with optimum amplitude resolution (NF)

Very good agreement between measurements and MC simulations

Page 13: Progress on signal processing techniques for Lumical ... · sources – laser, 90Sr source, generator • Good qualitative agreement for results obtained with different sources •

Deconvolution studied with various signal sources – laser, 90Sr source, generator

• Good qualitative agreement for results obtained with different sources

• Some quantitative differences are connected to :

– For generator relatively long rise time > 2.5ns

– For radioactive source (90Sr) poor timing resolution of reference photomultiplier signal

– Laser gives the most precise measurement

Tpeak

= Tsmp

= 60ns

Page 14: Progress on signal processing techniques for Lumical ... · sources – laser, 90Sr source, generator • Good qualitative agreement for results obtained with different sources •

Deconvolution results vs sensor bias voltages – pulse shape degradation

• Weak electric field (low HV) increases charge collection time and lengthen current pulse

• Non delta like pulse causes deviation from ideal CR-RC shaping

• Deteriorated pulse shape causes quantitative decrease of timing resolution

Tpeak

= 60ns

Altogether quantitative differences are not very big, the method is moderately sensitive to pulse shape

Page 15: Progress on signal processing techniques for Lumical ... · sources – laser, 90Sr source, generator • Good qualitative agreement for results obtained with different sources •

Deconvolution Summary

• Extraction of time and amplitude information using the deconvolution principle has been studied with MC simulations and verified experimentally

• Deconvolution performed on measured (with laser) data with the setup comprising of: sensor + Front-End + ADC shows very good agreement with MC simulations

• Precise timing information down to 1-2ns, good amplitude reconstruction and pileup rejection was obtained using a simple CR-RC shaper and T

peak=60ns

• Readout comprising of Front-End + ADC + DSP is a very good candidate for use in triggerless systems (CLIC / testbeam), replacing traditional dual chain readouts

• Subnanosecond resolution may be possibly obtained using shorter shaping/sampling times or multilayer detector systems, but have not been studied yet...

Page 16: Progress on signal processing techniques for Lumical ... · sources – laser, 90Sr source, generator • Good qualitative agreement for results obtained with different sources •

Deconvolution Future plans

• Short term : Verify fully custom triggerless system on testbeam (July 2011, see Adrian Matoga & Jonathan Aguilar talks)

• Long term : work in progress on extending the analyses (and measurements if possible) of deconvolution performance on:– optimization of power consumption, sampling time, shaping time for

given specifications

– precise calculation of correlated noise for given shaping/sampling

– implementation of higher order shaping like CR-RCn

– study ADC quantization effects

– study pileup effects

LumiCal Front-end ASIC Multichannel ADC ASIC Xilinx FPGA

Page 17: Progress on signal processing techniques for Lumical ... · sources – laser, 90Sr source, generator • Good qualitative agreement for results obtained with different sources •

Occupancy estimation for LumiCal@CLIC

(by Tel Aviv group)

• CLIC train structure :

– BX separation : 0.5ns

– BX per train 320 (whole train 160ns)

1% occupancy : → 3 hits per train → event separation ~ 50 ns

Page 18: Progress on signal processing techniques for Lumical ... · sources – laser, 90Sr source, generator • Good qualitative agreement for results obtained with different sources •

Technique for high occupancy CLIC

detectors – gated integrator & CDS

Page 19: Progress on signal processing techniques for Lumical ... · sources – laser, 90Sr source, generator • Good qualitative agreement for results obtained with different sources •

Gated Integrator - properties

• Simplest possible shape (step) will allow amplitude information reconstruction even in case of high occupancy

• Time resolution of single event tagging limited by rise time of preamplifier and ADC sampling frequency

• Feasible sampling frequencies :

– Only (fast) ADC : ~ 50 - 100 Msps (10 - 20ns)

– Analog memory followed by (slow) ADC : ~ 100 - 200 Msps (5 - 10ns)

• Dynamic range ~ 10 (12) bits

• SNR – to be estimated

Page 20: Progress on signal processing techniques for Lumical ... · sources – laser, 90Sr source, generator • Good qualitative agreement for results obtained with different sources •

Gated Integrator - Future plans ...

• We have already some prototypes with can be used to verify this concept

• Singal to Noise study has to be performed

• More information about time structure of incoming events is needed

Marek Idzik talkFCAL Collaboration Meeting

LAL-Orsay, France, 5-6 Oct. 2007

Page 21: Progress on signal processing techniques for Lumical ... · sources – laser, 90Sr source, generator • Good qualitative agreement for results obtained with different sources •

Summary

• Two methods for signal processing for CLIC detectors were presented

– Deconvolution gives very good results (both in amplitude and time domain) for relatively rare pulses (time interval > ~ 50ns)

– Gated integrator may be solution capable to process very high occupancy channels (signal to noise performance and time resolution are worst than for other methods)

• More information about time structure of incoming events / occupancy is needed

Page 22: Progress on signal processing techniques for Lumical ... · sources – laser, 90Sr source, generator • Good qualitative agreement for results obtained with different sources •

Backup slides

Page 23: Progress on signal processing techniques for Lumical ... · sources – laser, 90Sr source, generator • Good qualitative agreement for results obtained with different sources •

Very soon scope digitizer will be replaced by our new Multichannel ADC SoC ASIC

ADC ASIC 3rd prototype• 8 channels of 10 bit pipeline ADC

(verified to work up to 50Msps)

• Power scales linearly with fsmp

• Power switching on/off mechanism

• Cross talk < -70dB

• Digital multiplexer/serializer:

– Serial mode (max fsmp

~ 4 MSps)

– Parallel mode (max fsmp

~ 30MSps)

– Test mode (single channel readout)

• High speed LVDS drivers (~1GHz)

• Low power DAC control references

• Precise BandGap reference source

• Temperature sensor

• Die size ~ 2 x 3 mm ADC ASIC 2rd prototype

~ 0.8mW/MSps

Page 24: Progress on signal processing techniques for Lumical ... · sources – laser, 90Sr source, generator • Good qualitative agreement for results obtained with different sources •

Front-end Electronics & Sensor(designed for LumiCal detector@ILC)

Front-end spec:

– Cdet

≈ 0 ÷ 100pF

– 1st order CR-RC shaper (Tpeak

≈ 60 ns)

– variable gain

– SNR ~ 20 for MIP

Standard Silicon sensor :– Thickness 300um

– Capacitance ~ 5 – 25 pF / channel

– Leakage current ~ 5nA / channelAMS 0.35 μm

ASIC contains 8 channels

See more : M. Idzik, Sz. Kulis, D. Przyborowski "Development of front-end electronics for the luminoisty detector at ILC" Nucl. Instr. and Meth. A 608 (2009) pp.169-174

Page 25: Progress on signal processing techniques for Lumical ... · sources – laser, 90Sr source, generator • Good qualitative agreement for results obtained with different sources •

Few definitions

(for many events)

NF=20 log10 ( SNR%in

SNRout)

•Noise Figure (definition)

• (definition)

Recovered time = mean valueTime recovery error = RMS of such distribution

• NF = 0 → SNR doesn't change

• NF < 0 → SNR increases

• NF > 0 → SNR decreases

SNRin

= 20

• NF = 1db → SNRout

= 17.8

• NF = 2db → SNRout

= 15.9

• NF = 3db → SNRout

= 14.1

Page 26: Progress on signal processing techniques for Lumical ... · sources – laser, 90Sr source, generator • Good qualitative agreement for results obtained with different sources •

Deconvolution related issues

• How sampling time / peaking time / SNR affects timing resolution?

• What is optimum relation between sampling time, peaking time and power consumption?

• How deconvolution impacts on SNR ?• How pulse non-ideality affects deconvolution ?• How ADC resolution impacts on deconvolution ?

A dedicated experimental setup comprising of the whole readout chain (sensor + Front-End + ADC) was build to answer quantitatively some of these questions

Page 27: Progress on signal processing techniques for Lumical ... · sources – laser, 90Sr source, generator • Good qualitative agreement for results obtained with different sources •

Deconvolution – history, goals

• Deconvolution idea was proposed for use in pulse shaping in HEP experiments at the beginning of 90's

• It was then implemented in different versions of APV's (analog pipeline voltage) ASICs designed for synchronous with beam experiments like CMS at LHC, where deconvolution was performed by analog pulse shape processor (APSP)

• The main goal was amplitude measurement with good pileup rejection plus a rough estimation of time (to identify beam crossing, repeating every 25ns)

• Our goals are to:

– apply deconvolution principle in asynchronous systems

– obtain precise timing information (~1-10 ns rms) in addition to amplitude and good pileup rejection

– add ADC in each readout channel and use digital signal processing (much more robust than analog)

Page 28: Progress on signal processing techniques for Lumical ... · sources – laser, 90Sr source, generator • Good qualitative agreement for results obtained with different sources •

Deconvolution – principle and choice of adequate shaping

Requirements :– Simple hardware shaper realization

– Simple deconvolution formula

V sh s =1

s1/2

D s =1

V sh s=s1 /2

I sen t = t I sen s =1

z=esT

- peaking time

D z =z2−2 e−T /e−2T /

z-1 is a unit time delayT – sampling interval

d t i=z−1 D z =V sh t i−2e−T /V sh t i−1e−2T /V sh t i−2

CR-RC shaper

Sensor pulse: CRRC response

Deconvolution formula (s domain)

Deconvolution formula (time domain)

Deconvolution formula (z domain)

d t i=V sh t i−0.74V sh t i−10.14V sh t i−2

=TFor :

Page 29: Progress on signal processing techniques for Lumical ... · sources – laser, 90Sr source, generator • Good qualitative agreement for results obtained with different sources •

CLIC machine time structure – Power savings

Average power can be reduced 20ms/200ns ~= 100.000 times ! if switching on/off mechanism is implemented

Page 30: Progress on signal processing techniques for Lumical ... · sources – laser, 90Sr source, generator • Good qualitative agreement for results obtained with different sources •

Deconvolution alghoritm

• Look Up Tables used• Time and amplitude finding can be done off-line or in

external DAQ

Page 31: Progress on signal processing techniques for Lumical ... · sources – laser, 90Sr source, generator • Good qualitative agreement for results obtained with different sources •

Event processing

• Interpolation is used to find trigger time (< 250ps)

• Acquired (oversampled 4 Gsps) waveform is down-sampled to number of events for further analyses (but trigger information is left precise)

Testing all possibles phases between sampling clock and incoming event