9 th International Front-End Electronics meeting Fermilab – Argonne 2014 A. Dragone*, P....

9th International Front-End Electronics meeting Fermilab – Argonne 2014

A. Dragone*, P. Caragiulo, B. Markovic, R. Herbst, K. Nishimura, B. Reese, S. Herrmann, P. Hart, G. Blaj, J. Segal, A. Tomada, J. Hasi, G. Carini, C. Kenney, G. Haller

ePix: a class of architectures for second generation LCLS cameras

(* [email protected])

RED Integrated Circuits Dept.

2

Outline

• Introduction- A few words on LCLS detector needs (more in Sven Herrmann’s talk)

• The ePix approach: platform based ASIC architectures- Architectural choices

- ePix platform

• ePix100 and ePix10k ASIC variants- Pixel designs

- Prototypes performance

• Summary and conclusions

FEE 2014, Fermilab-Argonne

LCLS: the first hard X-ray FEL source

LCLS - Undulators Hall

3FEE 2014, Fermilab-Argonne

• Operational since 2009 • Six instruments:

• AMO (500 – 2000eV)• CXI (5 – 10keV)• MEC (4 – 10keV)• SXR (250 – 2000eV)• XCS (5.5 – 10keV)• XPP (4 – 10keV)

LCLS – main characteristics

• Pulsed (up to120Hz)• Pulses are very short (~30 - 200fs) • Monochromatic • Extreme peak brightness • Spatially coherent

Other FELs

• FLASH - (since 2005, DESY, Germany)• SACLA XFEL - (since 2011, Japan) • PAL XFEL (South Korea)• SwissFEL (Swiss)• European XFEL (Germany)

Pulsed sources Integrating detectorsHigh repetition rate Fast readout

No matching commercial camera available:• Compromise• Dedicated detector development

4

Detector needs (more in S. Herrmann talk)

•High Dynamic Range Front End (1- >104 photons )- The extremely high brilliance of X-ray FEL sources

enables single shot experiments with sufficient resolution (ρ=1/√(Nph·DQE))

•Large Detector Area (common to several experiments)- Diffraction techniques with atomic resolution require

large angular coverage (~2rad)

•Small Pixel Size and Low Noise- Coherence property of the X-ray FEL sources

enables X-ray Photon Correlation Spectroscopy techniques. To resolve speckle patterns small pixel 50um or below and large area detector are often required.


S. Boutet et al., “High-Resolution Protein Structure Determination by Serial Femtosecond Crystallography”, Science.1217737 (2012).

5

Parallelism and time division multiplexing: some guidelines

- S

en

sor

arc

hite

ctu

re c

om

ple

xity

an

d d

eve

lop

me

nt

time

incr

ea

se

+ ASIC Development Time

Serial Readout

Column Parallel Readout

Hybrid Pixel

3D

Hybrid Pixel Hybrid Pixel

ADC

ADC

ADC

Column Parallel Readout

+ Frame Rate

Min Parallelism

Max Parallelism

External A to D conversion variants

- Input capacitance (noise)+ Power per channel+ ASIC front-end complexity- System complexity+ Radiation tolerance (technology)

+ Frame rate- Power distribution complexity+ ASIC back-end complexity+ System scalability

+ Analog pixel

+ No digital activity during integration

+ More space for filtering

+ Robust high res. low power ADC

+ Minimum clock rates

+ Frame rate not limited by the readout time- Long hold time in the analog memory- Larger balcony (gaps)FEE 2014, Fermilab-Argonne

6

Modularity and scalability: Platform based designsD

AQ

• Cameras require a top down design approach using common platforms.• The platform is defined by standardized interfaces and communication protocols between the

various components of the detector• A minimum set of key components has multiple variants (ASIC and assemblies)

• Several variants of ASIC/sensor combinations with a common communication BE up to the DAQ.

• Variants can be housed in several module assembly

• Facilitates integration of one or multiple detectors into a combined camera of various sizes and shapes (rectangular planes, curved arcs)

• Combinations can even include modules with different functionalities

Standard communication protocol between DAQ and BE electronics

Standard configuration and communication protocol with minimum I/Os between ASIC and BE electronics.

BE electronics

ASICs with a common BE and different functionalities designed at the pixel level

Sensors with different pixel size to match different pixel implementations

High Dynamic Range variant

Ultra low noise variant

Multiple compatible modules assembly


352

96

4

ΣΔ ΣΔ ΣΔ

DEC DEC DEC

ΣΔ

DEC

Temp

Row

sel

ecto

rSerializer

LVDS Output Buffers

CMD unit SACI

Bias

Global Registers

ePix architecture highlights

7

ePix100 ePix10kMode of Operation INT INT-with auto-rangingTechnology 0.25 µm 0.25 µmPixel size 50x50 µm2 100x100 µm2

Array 352x384 176x192Full Size Full Reticule Full ReticuleFrame rate 120Hz (> 1kHz) 120Hz (> 1kHz)Range 220ke- 22Me-

Effective ENC <100e- (50e-) <350e- (120e-)FE Gain 6.5µV/e- 6.5µV/e- ,64nV/e-

Polarity positive positiveFiltering LP + cds LP + cdsS/N 44 8.8DC Power cons. < 10µW/pix < 10µW/pix Power pulsing (PP) Yes YesPP Power cons. < 3µW/pix @ 120Hz < 3µW/pix @ 120Hz

Pixel Matrix: fully analog. Different designs for each detector variants• Pre-amplifies signals • Filters signals• Samples signals (with CDS)

Balcony (ePix platform): • Controls Configuration• Controls Acquisition and Readout• Performs Analog to Digital Conversion• Provides Calibration and Monitoring support


ePix(A) intermediate step – status of the project

352

96

4

Buf. Buf. Buf.

Temp

Row

sel

ecto

r

Diff. Analog Buffer

CMD unit SACI

Bias

Analog Monitor Global Registers

analog balcony

• Columns are read sequentially

• Limited read-out speed (120Hz - 8ms)

• 5MHz clock required• Back-end noise limited

(ePix100)

Column selector

ePix (P) - minimum area matrix prototypes with analog balcony

ePix (A) – final size with analog balcony

ePix (F) - full matrix with digital balcony

ADC

ADC

ADC

ePix100p designed, fabricated testedePix10kp designed, fabricated tested

To mitigate risks and to bridge the gap of the development time and intermediate version of ePix using external ADC

ePix design phases:

ePix100a designed and in fabricationePix10ka designed and ready for submission

Digital balcony in design

FEE 2014, Fermilab-Argonne 8

SACI

Acquisition

Idle phase: non vital resources kept in power saving mode

Wake up phase: all resources get ready to run

Acquisition phase: analog processing in pixels active, no digital activity (balcony in power saving mode)

Readout phase: matrix readout A/D conversion, data serialization and transmission (non vital pixel analog blocks in power saving mode)

Global Registers, In pix registers (gain, calib., analog monitor)

8ms

LCLS Pulses

8ms

… …ROclk

AQCUse only 3 signals

Res, AQC and ROclk

Use only 4 signalsand a control interface based on a

SLAC configuration protocol (standard platform)

Res

ePix phases of operation


Pixel Matrix with Random Access

• In configuration phase a command unit pushes addresses into the counters providing access to the pixels. Single rows or columns can also be accessed in parallel as well as the full matrix

• In acquisition phase the row counter (both in the ver. A) scan the matrix in a windows defined by the addresses stored in the Rows and Columns start and stop registers

Pix Bank 1352x96

Pix Bank 2352x96

Pix Bank 3352x96

Pix Bank 4352x96

Row

de

cod

er

(Gra

y to

On

e H

ot)

352

96 96 96 96

Column Decoders (Gray to One Hot)

Bin

ary

Pro

gram

mab

le T

rue

Gra

y C

ount

er (

9 bi

ts)

9

Binary Programmable True Gray Counter (7 bits)

7

Row

Sta

rt R

eg.

Row

Sto

p R

eg.

9

9

Col Start Reg. Col Stop Reg.

7 7

ROclk

Pixel (0,0)

ePix pixel matrix access protocol


SLAC ASIC Control Interface (SACI)

Motivation

• Need simple serial interface to ASICs for

configuring registers and sending

commands.

Standard Options Not a Great Fit

• SPI: No backpressure. No way for ASIC

to signal that it is done with a command

or ready for new data. Requires polling.

• I2C: Backpressure possible through clock

stretching, but complex protocol and

implementation.

Master/Slave Serial Interface

4 Signals

• 3 shared: saciClk, saciCmd, saciRsp

• 1 dedicated select line per slave: saciSelL

Allows multiple slaves on same SACI bus. (Similar to SPI.)

• 320 Standard Cells

• 98.52 µm x 540.20 µm


Why sigma delta?

12

Noise Shaping

We are here

Ʃ-Δ

SAR

Pipeline

Flash

Ʃ-Δ

Sigma-delta present several advantages:• They are compatible with frame rates of 500-1kHz required by the application

• Allow trading resolution for clock speed (oversampling ratio). Different pixel variants may require different resolutions

• They provide noise shaping

• Have a pseudo-random nature which reduces cross-talk effects between channels

• Require low precision analog blocks and have simple implementation (small area)

• Have potential for upgrades in more advanced technologies (heterogeneous integration)

Optimal ADC architecture is a compromise among sampling rate, resolution, digital multiplexing, serialization rate and development time


• Gain calibration (per pixel)- charge can be injected in each single pixel or group of pixels. A 10-bit DAC can set the amount of

injected charge in constant or automatic scan mode.

• Frame common mode tracking (In frame)- at the end of each frame the baseline and the max charge values are digitized on each column.

This feature provides the possibility to track baseline shifts.

• Temperature tracking and compensation- a temperature variations compensation scheme is present.

• Analog and Digital monitors- critical internal nodes can be monitor during debugging and to check the correct functioning

during operation

ePix calibration, compensation and monitoring


“Any detector is only as good as it’s calibration” S. Gruner

ePix100 pixel architecture


ePix100 noise weighting function

15

Vout at 100ph @ 8keV Vout at 1ph @ 8keV


ePix100a pixel layout 50µm x 50µm

~ 28 million transistors

16

50 µm

50 µm


ePix100 prototype 96x96 pixels

ePix100p balcony close up ePix100p pixel close up

ePix100p pixel layout

ePix10k pixel architecture


ePix10k pixel response

• High Gain = 42mV/fC or 6.5µV/e-

• Low Gain = 398mV/pC or 64nV/e-

• Auto-ranging• Forced Switched Low Gain

Non-Linearity < 0.05%

18

•1024 pixels•Auto-ranging (multiple gains), •Multiple sampling per train, •Power pulsing

D. Freytag et al., IEEE Nucl. Sci. Symp. Conf. Rec. (2008) 3447

KPiX SLAC; similar implementation successfully used in HEP:

4 Modes of operation:


Simulated Noise: 120e- r.m.s.

ePix10ka pixel layout 100µm x 100µm

~ 20 million transistors

19

100 µm


ePix10k prototype 48x48 pixels

ePix10kp balcony close up ePix10kp pixel close up

ePix10kp pixel layout

100 µm

20

ePix100a expected power consumption

DC mode Power pulsed mode

10 µW/pixel 3 µW/pixel

Eiger 8.8µW/pixel

Timepix3 14µW/pixel

Medipix3 9µW/pixel

FEI4 10µW/pixel


21

ePix100 pixel linearity and gain measurements

Gain slightly lower than nominal. Compatible with parasitic capacitances around the feedback capacitor:

Measured equivalent Cf = 27.5fF


22

Columns

Ro

ws

10 20 30 40 50 60 70 80 90

10

20

30

40

50

60

70

80

90370

375

380

385

390

395

ePix100 gain uniformity measurement

Good Uniformity of gain across the full matrix is achieved:

Flatness across rows < 1count/fC i.e. max 0.26%

Flatness across columns < 2count/fC i.e. max 0.52%

ePix100p gain map


365 370 375 380 385 390 395 4000

100

200

300

400

500

600

700

800

900

1000

Gain [ADC Counts per fC]

Nu

mb

er o

f P

ixel

s

y(x) = a exp( - ((x - x0) 2̂) / (2 .̂..

a = 983.72 = 1.1148x

0 = 382.36

R = 0.99754 (lin)

Overall gain distribution and dispersion:

Gain dispersion of 1.11 count/fC is achieved i.e. ~0.3%

The result is compatible with the typical dispersion of MIM capacitors and expected gain variations in the pixel analog chain

23

Dark frame uniformity: fixed patterns

Columns

Ro

ws

10 20 30 40 50 60 70 80 90

10

20

30

40

50

60

70

80

90 1300

1400

1500

1600

1700

1800

1900

2000

Fixed pattern noise is visible across columns as expected considering the layout arrangement of the pixels in the matrix (groups of 16 with mirror image every column)

Good flatness of the dark field is achieved:

Flatness across rows < 150 counts i.e. max 0.9%

Flatness across columns < 100 counts i.e. max 0.6%

ePix100p darkframe (1000 frames averaged)


Columns

Row

s

10 20 30 40 50 60 70 80 90

10

20

30

40

50

60

70

80

90

2

2.5

3

3.5

4

4.5

5

ePix100p noise (darkframe subtracted)

Good noise uniformity across the full matrix is achieved:

Flatness across rows < 0.2 count i.e. max 6%

Flatness across columns < 0.1 count i.e. max 3%

24

ePix100 noise performance

a sigma of 3.2 counts r.m.s. is equivalent to about 50e- r.m.s. i.e. a S/N ratio of 44 for

single photon at 8keV

-30 -20 -10 0 10 20 300

200

400

600

800

1000

1200

1400

ADC Counts

y(x) = a exp( - ((x - x0) 2̂) / (2 .̂..

a = 1301.4 = 3.0391x

0 = 0.01

R = 0.99807 (lin)

Single pixel noise distribution

-40 -30 -20 -10 0 10 20 30 400

1

2

3

4

5

6

7x 10

6

ADC Counts

y(x) = a exp( - ((x - x0)^2) / (2 ^...

a = 6.8752e+006 = 3.2997x

0 = 0.056757

R = 0.99997 (lin)


All pixels cumulative noise distribution

Distribution of the pixel noise (r.m.s.) across the matrix

Noise dispersion among pixels is on the order of 2%

3 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.90

460

920

1400

ADC Counts

y(x) = a exp( - ((x - x0) 2̂) / (2 .̂..

a = 14.046 = 0.070021x

0 = 3.2543

R = 0.98227 (lin)

25

ePix100: first results with a bonded sensor

ePix sensor first test (left to right): P. Hart, K. Nishimura, S. Herrmann, G. Blaj, P. Caragiulo, B. Markovic

ePix100p sensor bump bonded on a ePix100p ASIC.


ASIC/Sensor Single pixel Noise performance under a x-ray tube with a Molybdenum target. (Integration time 10 times longer than planned for LCLS, no temperature control ~40 °C. Leakage fluctuations present).

Noise of 5.7 counts r.ms. ~ 90e- r.m.s.

(without optimization already compatible with the application requirement of 100e- r.m.s.) Charge sharing reconstructed - G. Blaj

26

ePix100: first results with a bonded sensor at LCLS

LCLS: 9.5keV beam hitting a Cu target with a Fe one on top

ePix100: set in x2 output gainC

ou

nts

ADU

Cu

Fe

G. Carini, S. Herrmann et al.

27

ePix10k pixel linearity and gain measurements

High Gain slightly lower than nominal. Compatible with parasitic capacitances around the feedback capacitor:

Measured equivalent Cf = 30fF


0 100 200 300 400 500 600 700 800 900 1000

4000

5000

6000

7000

8000

9000

10000

11000

12000

13000

14000

Pulser

AD

C C

ou

nts

0 100 200 300 400 500 600 700 800 900 1000

4000

6000

8000

10000

12000

14000

Pulser

AD

C C

ou

nts

0 100 200 300 400 500 600 700 800 900 1000

-8

-6

-4

-2

0

2

4

Pulser

INL

[A

DC

co

un

ts]

0 100 200 300 400 500 600 700 800 900 10000.4

0.6

0.8

1

1.2

1.4

1.6

x 104

Pulser

AD

C C

ou

nts

Pulser in HR

Pulser in LR

Pulser in HR

Fixed High Gain

Fixed Low Gain

Fixed Low Gain

Auto-range

28

ePix10k gain uniformity measurement

Good Uniformity of gain across the full matrix is achieved in both High Gain and Low Gain

ePix10kp gain maps:


Overall gain distribution and dispersion:

A gain dispersion of ~0.4% in High Gain and of ~ 0.3% in Low Gain have been achieved

137.5 138 138.5 139 139.5 140 140.5 141 141.5 142 142.50

20

40

60

80

100

120

140

Gain [ADU/Pulser DAC units]

Nu

mb

er

of

Pix

els

y(x) = a exp( - ((x - x0)^2) / (2 .̂..

a = 126.19 = 0.60442x

0 = 140.13

R = 0.9926 (lin)

High Gain Low Gain

1.685 1.69 1.695 1.7 1.705 1.71 1.715 1.72 1.725 1.730

20

40

60

80

100

120

140

160

180

Gain [ADU/Pulser DAC units]

Nu

mb

er

of

Pix

els

y(x) = a exp( - ((x - x0) 2̂) / (2 .̂..

a = 155.42 = 0.0044952x

0 = 1.7054

R = 0.99326 (lin)

Columns

Row

s

10 20 30 40

5

10

15

20

25

30

35

40

45135

140

145

Columns

Row

s

10 20 30 40

5

10

15

20

25

30

35

40

451.65

1.7

29

Dark frame uniformity: fixed patterns

Fixed pattern noise is visible across columns as expected considering the layout arrangement of the pixels in the matrix (groups of 16 with mirror image every column)

Good flatness of the dark field is achieved:

Flatness across rows < 80 counts i.e. max 0.4%

Flatness across columns < 120 counts i.e. max 0.6%

ePix10kp darkframe (1000 frames averaged)


ePix10kp noise (darkframe subtracted)

Good noise uniformity across the full matrix is achieved:

Flatness across rows < 0.4 count i.e. max 6%

Flatness across columns < 0.2 count i.e. max 3%

Columns

Ro

ws

5 10 15 20 25 30 35 40 45

5

10

15

20

25

30

35

40

45

1800

1900

2000

2100

2200

2300

2400

2500

2600

Columns

Ro

ws

5 10 15 20 25 30 35 40 45

5

10

15

20

25

30

35

40

45

4

5

6

7

8

9

10

6 6.2 6.4 6.6 6.8 7 7.2 7.4 7.6 7.8 80

50

100

150

200

250

300

350

400

ADC Counts

y(x) = a exp( - ((x - x0) 2̂) / (2 .̂..

a = 339.55 = 0.32752x

0 = 6.9506

R = 0.99451 (lin)

-40 -30 -20 -10 0 10 20 30 400

2

4

6

8

10

12

14

16x 10

4

ADC Counts

y(x) = a exp( - ((x - x0)^2) / (2 .̂..

a = 1.5725e+005 = 6.8069x

0 = -0.011614

R = 0.99996 (lin)

30

ePix10k noise performance

a sigma of 6.7 counts r.m.s. is equivalent to about 120e- r.m.s. i.e. a S/N ratio of 18 for

single photon at 8keV

Single pixel noise distribution


All pixels cumulative noise distribution

Distribution of the pixel noise (r.m.s.) across the matrix

Noise dispersion among pixels is on the order of 5%

-30 -20 -10 0 10 20 300

20

40

60

80

100

120

140

160

180

200

ADC Counts

y(x) = a exp( - ((x - x0)^2) / (2 .̂..

a = 180.35 = 6.7456x

0 = 0.16766

R = 0.99377 (lin)

31

ePix10k: first results with a bonded sensor


AD

U

Photons (8keV)

Linearity scan low gain mode at LCLSX-ray tube with a Molybdenum target (high gain)

G. Carini, S. Herrmann et al.

Co

un

ts

ADU

CumulativeCumulative with gain correction

Summary

32

• SLAC is working on a new generation of hybrid pixel detectors for photon

science based on a modular platform approach that:- facilitates integration, scalability, versatility

- mitigates risks

- reduces development time and costs

• ePix is a class of front-end ASICs for integrating hybrid photon detectors- Based on a column parallel readout architecture with sigma delta ADCs

- Fully analog pixel matrix with filtering optimized for different areas of application• ePix-100 is optimized for ultra low noise applications. It has pixels of 50µmx50µm

size arranged in a 352x384 matrix. A resolution of 50e- r.m.s. and a signal range of

35fC (100 photons at 8keV) has been achieved. In its final version it will be able to

sustain a frame rate of 1kHz.

• ePix-10k is optimized for high dynamic range applications. It has pixels of

100µmx100µm size arranged in a 176x192 matrix. A resolution of less than 120e-

r.m.s. and a signal range of 3.5pC (10k photons at 8keV) has been achieved. In its

final version it will be able to sustain a frame rate of 1kHz.

• Tests on the ePix100 and ePix10k prototypes have demonstrated the approach

is sound. - In particular the platform has been proven to behave as required, allowing to

proceed with the submission of the full size variants ePix100a and ePix10ka.


ePix100p with some pixel injected using the automatic scan mode based on the internal pulser. The pulser injects in every frame an increased amount of charge in the selected pixels up to the full scale (100Ph @8keV).The interesting aspect of this movie is that all functionalities of the ASIC are used.

33

ePix10k weighting functions

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-0.2

0

0.2

0.4

0.6

0.8

1

t/Tm0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

t/Tm

AD

U


Weighting functions in high gain mode

For a small signal the filter has a long time constant and the function is quasi-trapezoidal

Passed the range switching the weighting function has a reduced amplitude. The effect of gating the comparator firing can be seen in the top right part.

Weighting functions in auto-range mode

CDS effects on auto-ranging – ePix approach

5 10 15 20 25 30 35 40 45 50 55

10

15

20

25

30

Signal / Noise vs R0 to Acq distance

Sig

nal /

Noi

se

R0 to Acq [us]

@ 1 8keV Ph

@ 1 8keV Ph fitted@ 100 8keV Ph

@ 100 8keV Ph fitted


In auto-ranging if a signal triggers the comparator, the CDS will subtract a baseline weighted with a larger gain, resulting in an excess noise in the second range.

Solutions: - read the 2 samples separately and

subtract only if the signal is in the first range

- don’t use CDS at all- or the ePix approach

Because the intervals of time reserved to sample the baseline and the signal are continuously adjustable in ePix; the CDS timings can be unbalanced resulting in a filtered version of the baseline sample with an effective lower gain. This is equivalent of reducing the efficiency of the CDS and increasing the S/N ratio at the switching point.

Trade off between S/N ratio at the switching point and at the minimum signal in ePix10k auto-range mode

There is an optimal point at which the S/N is larger than 14 (150e- in the first range) in both ranges

35

20 30 40 50 60 70 80 90

1000

1500

2000

2500

3000

3500

4000

Carrier Temperature (°C)

Dum

my

Pix

el B

asel

ine

(AD

U)

y(x) = a x + ba = 20.826b = 1835R = 0.9941 (lin)

y(x) = a x + ba = -0.87013b = 1632.9R = 0.44481 (lin)

TCePix (uncompensated) = 20.8 ADU/°C

TCePix (compensated) = -0.9 ADU/°C

After proper calibration a TC between +- 0.2 ADU/°C is expected


ePix100 temperature compensation circuitry (preliminary)

9 th International Front-End Electronics meeting Fermilab – Argonne 2014 A. Dragone*, P....

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Transcript of 9 th International Front-End Electronics meeting Fermilab – Argonne 2014 A. Dragone*, P....