1. Infrared Detector & ASIC Technology
Markus Loose
STScI, May 8, 2014

2. Outline CMOS-based Detectors (infrared) Control ASICs Conclusion
General Properties of Solid State Detectors
CMOS-based Multiplexers
Examples
Control ASICs
General Description
Example: SIDECAR ASIC
Preamp, Biases, ADCs
Noise performance and issues
Conclusion
May 08, 2014
STScI Lecture

3. CMOS-based Infrared Sensors
( CMOS: Complimentary Metal Oxide Silicon )
May 08, 2014
STScI Lecture

4. Scientific Detector Workshop, Garching, Germany
The Ideal Detector
Detect 100% of photons
Each photon detected as a delta function
Large number of pixels
Time tag for each photon
Measure photon wavelength
Measure photon polarization
Up to 98% quantum efficiency
One electron for each photon gfdg
~1,400 million pixels (>109)
No - framing detectors
No – defined by filter
Plus Read Noise and other “Features”
Oct 15, 2009
Scientific Detector Workshop, Garching, Germany

5. Hybrid Imager Architecture
Image of indium bump array in comparison to human hair
(credit: Laser Focus World)
May 08, 2014
STScI Lecture

6. Energy of a Photon
Wavelength (m)
Energy (eV)
Band
0.3
4.13 UV
0.5
2.48
Vis
0.7
1.77
1.0
1.24
NIR
2.5
0.50
SWIR
5.0
0.25
MWIR
10.0
0.12
LWIR
20.0
0.06
VLWIR
Energy of photons is measured in electron-volts (eV)
eV = energy that an electron gets when it “falls” through a 1 Volt field.
May 08, 2014
STScI Lecture

7. An Electron-Volt (eV) is extremely small
1 eV = 1.6 • J (J = joule)
1 J = N • m = kg • m • sec-2 • m
1 kg raised 1 meter = 9.8 J = 6.1 • 1019 eV
The energy of a photon is VERY small
The energy of a SWIR (2.5 m) photon is 0.5 eV
Drop a peanut M&M® candy from a height of 2 inches
Energy is equal to 6 x 1015 eV (a peanut M&M® is ~2 g)
This is equal to 1.2 x 1016 SWIR photons
1 million x 1 million x 12,000
The number of photons that will be detected in ~1 million images from the James Webb Space Telescope (JWST)
A 2-inch peanut M&M® drop is more energy than will be detected during the entire 5-10 year lifetime of the JWST !
May 08, 2014
STScI Lecture

8. Photon Detection Eg (eV) c (m)
For an electron to be excited from the
conduction band to the valence band
h > Eg
h = Planck constant ( Joule•sec)
= frequency of light (cycles/sec) = /c
Eg = energy gap of material (electron-volts)
Conduction Band Eg
Valence Band
c = / Eg (eV)
Material Name
Symbol
Eg (eV)
c (m)
Silicon Si
1.12
1.1
Indium-Gallium-Arsenide
InGaAs
0.73 – 0.48
1.68 – 2.6
Mercury-Cadmium-Teluride
HgCdTe
1.00 – 0.07
1.24 – 18
Indium Antimonide
InSb
0.23
5.5
Arsenic doped Silicon
Si:As
0.05 25
May 08, 2014
STScI Lecture

9. General CMOS Detector Concept
CCD Approach
CMOS Approach
Pixel
Charge generation &
charge integration
Charge generation, charge integration & charge-to-voltage conversion +
Photodiode
Amplifier
Array Readout
Charge transfer from pixel to pixel
Multiplexing of pixel voltages: Successively connect amplifiers to common bus
Sensor Output
Output amplifier performs charge-to-voltage conversion
Various options possible:
no further circuitry (analog out)
add. amplifiers (analog output)
A/D conversion (digital output)
May 08, 2014
STScI Lecture

10. General Architecture of CMOS-Based Image Sensors
Bias Generation & DACs
(optional)
Control &
Timing
Logic (optional)
Vertical Scanner for Row Selection
Pixel Array
A/D conversion (optional)
Digital Output
Horizontal Scanner / Column Buffers
Analog Amplification
Analog Output
May 08, 2014
STScI Lecture

11. IR Multiplexer Pixel Architecture
Vdd
amp drain voltage
Output
Detector
Substrate
Photvoltaic
May 08, 2014
STScI Lecture

12. IR Multiplexer Pixel Architecture
Vreset
reset voltage
Reset
Vdd
amp drain voltage
Output
Detector
Substrate
Photvoltaic
May 08, 2014
STScI Lecture

13. IR Multiplexer Pixel Architecture
Vdd
amp drain voltage
Vreset
reset voltage
Reset
Enable
“Clock” (red)
“Bias voltage” (purple)
Output
Detector
Substrate
Photvoltaic
May 08, 2014
STScI Lecture

14. Special Scanning Techniques in CMOS
Different scanning methods are available to reduce the number of pixels being read:
Allows for higher frame rate or lower pixel rate (reduction in noise)
Can reduce power consumption due to reduced data
Windowing
Reading of one or multiple rectangular subwindows
Used to achieve higher frame rates (e.g. AO, guiding)
Subsampling
Skipping of certain pixels/rows when reading the array
Used to obtain higher frame rates on full-field images
Random Read
Random access (read or reset) of certain pixels
Selective reset of saturated pixels
Fast reads of selected pixels
Binning
Combining several pixels into larger super pixels
Used to achieve lower noise and higher frame rates
* Binning is typically less efficient
in CMOS than in CCDs.
May 08, 2014
STScI Lecture

15. Possible Reset Schemes for HxRG
Stitched CMOS Sensor
Reticle
May 08, 2014
STScI Lecture

16. Astronomy Application: Guiding
Special windowing can be used to perform full-field science integration in parallel with fast window reads.
Simultaneous guide operation and science data capture within the same detector.
Two methods possible:
Interleaved reading of full-field and window
No scanning restrictions or crosstalk issues
Overhead reduces full-field frame rate
Parallel reading of full-field and window
Requires additional output channel
Parallel read may cause crosstalk or conflict
No overhead  maintains maximum full-field frame rate
Full field row
Window
Full field row
Window 16
May 08, 2014
STScI Lecture

17. Guide Mode Demonstration
Video shows a small window in the center, read frequently for guiding, while the full field is read slowly in the background
May 08, 2014
STScI Lecture

18. Teledyne HAWAII-2RG Hybrid Detector Array
HgCdTe Astronomy Wide Area Infrared Imager
with 2k2 Resolution, Reference pixels and Guide Mode
2k x 2k HAWAII-2RG with HyViSI detector
2 x 2 Mosaic of HAWAII-2RG detectors
May 08, 2014
STScI Lecture

19. H2RG Block Diagram All pads located on one side (top)
Approx. 110 doubled I/O pads (probing and bonding)
Three-side close buttable
18 µm pixels
Total dimensions: 39 x 40.5 mm²
May 08, 2014
STScI Lecture

20. JWST - James Webb Space Telescope 15 Teledyne 2K×2K infrared arrays on board (~63 million pixels)
International collaboration
6.5 meter primary mirror and tennis court size sunshield
2018 launch on Ariane 5 rocket
L2 orbit (2.4 million km from Earth)
NIRCam
(Near Infrared Camera)
FGS / NIRISS
(Fine Guidance Sensors /
Near-Infrared Imager and Slitless Spectrograph)
NIRSpec
(Near Infrared Spectrograph)
Two 2x2 mosaics
of SWIR 2Kx2K
Two individual MWIR 2Kx2K
3 individual MWIR 2Kx2K
1x2 mosaic of MWIR 2Kx2K
Acquisition and guiding
Images guide stars for telescope stabilization
Canadian Space Agency
Spectrograph
Measures chemical composition, temperature and velocity
European Space Agency / NASA
Wide field imager
Studies morphology of objects and structure of the universe
U. Arizona / Lockheed Martin
May 08, 2014
STScI Lecture

21. Control ASICs
May 08, 2014
STScI Lecture

22. How to Operate an Image Sensor?
Sensor/Detector requires:
DC bias and reference voltages
Set properties like offset, bandwidth, reverse detector bias
Voltages need to be programmable to allow optimal performance
Very low noise to not contribute to the read noise (< 10µV noise)
Clocks/Digital control signals
Responsible for controlling the readout timing and sensor configuration
Configurable timing required
Video Signal Readout
If digital output sensor, job is mostly done. Simply route to FPGA for data acquisition and storage
If analog output sensor:
Amplify/buffer analog signal
Perform analog-to-digital conversion, then route digital data to FPGA
May 08, 2014
STScI Lecture

23. ASIC as Control Electronics
Replace this
with this!
1% volume 1% power
1% hassle
May 08, 2014
STScI Lecture

24. SIDECAR ASIC Architecture
System for Image Digitization, Enhancement, Control And Retrieval
May 08, 2014
STScI Lecture

25. SIDECAR ASIC Features 36 analog input channels, each channel provides:
500 kHz A/D conversion with 16 bit resolution
10 MHz A/D conversion with 12 bit resolution
gain = 0 dB …. 27 dB in steps of 3 dB
optional low-pass filter with programmable cutoff
optional internal current source (as source follower load)
20 analog output channels, each channel provides:
programmable output voltage and driver strength
programmable current source or current sink
internal reference generation (bandgap or vdd)
32 digital I/O channels to generate clock patterns, each channel provides:
input / output / high-ohmic
selectable output driver strength and polarity
pattern generator (16 bit pattern) independent of microcontroller
programmable delay (1ns - 250µs)
16 bit low-power microprocessor core (single event upset proof)
responsible for timing generation and data processing
16 kwords program memory (32 kByte) and 8 kwords data memory (16 kByte)
36 kwords ADC data memory, 24 bit per word (108 kByte)
additional array processor for adding, shifting and multiplying on all 36 data channels in parallel (e.g. on-chip CDS, leaky memory or other data processing tasks)
May 08, 2014
STScI Lecture

26. SIDECAR Operating a HAWAII-2RG / 1RG
Inside the dewar at cryogenic temperatures PC
SIDECAR ASIC
HAWAII-2RG
Sensor Chip Assembly
Software for SIDECAR Control and Data Capture
Analog Video
Vreset
Dsub
Clock
000 w
384
0cd
Biases
Power Supply
Data In
PCI Card
or USB interface
Serial Interface
Data Out
Clocks
Master Clock
3.3V
3.3V
Digital Supply
Analog Supply
Only 7 lines needed to operate the SIDECAR ASIC in base configuration (3 signal & 4 power lines)
The SIDECAR ASIC provides all 27 signals required to operate the HAWAII-2RG
The microcontroller driven SIDECAR ASIC generates all biases & clocks and digitizes the analog video outputs
May 08, 2014
STScI Lecture

27. SIDECAR ASIC Flight Package for JWST
Ceramic board with ASIC die and decoupling caps
Invar box with top and bottom lid
Two 37-pin MDM connectors
FPE-to-ASIC connection
ASIC-to-SCA connection
Qualified to NASA Technology Readiness Level 6 (TRL-6)
15 mW power when reading out of four ports in parallel, with 16 bit digitization at 100 kHz per port.
SCA side
FPE side
Comparison:
LGA Package
ACS (HST)
May 08, 2014
STScI Lecture

28. Missions Employing SIDECAR ASICs
James Webb Space Telescope
NIRCam, NIRSpec, FGS/NIRISS instruments
H2RG IR detectors, T = 38K (ASIC), planned launch in 2018
Hubble Space Telescope
ACS (Advanced Camera for Surveys)
CCD detector, T = 300K (ASIC), launched in 2009
Landsat Data Continuity Mission
TIRS (Thermal InfraRed Sensor) instrument
QWIP detector, T = 300K (ASIC), launched in 2013
OSIRIS-REx Asteroid Mission
OVIRS (OSIRIS-REx Visible and IR Spectrometer) instrument
H1RG IR detector, T = 300K (ASIC), planned launch in 2016
Euclid Mission
NISP (Near IR Spectrometer Photometer) instrument
H2RG IR detector, T = ~140K (ASIC), planned launch in 2020
MOSFIRE (Multi-Object Spectrometer For Infra-Red Exploration)
H2RG IR detector, T < 120K (ASIC), deployed at the Keck Telescope
FourStar Wide Field Infrared Camera
H2RG IR detector, T < 120K (ASIC), deployed at the Magellan Baade 6.5m Telescope
JWST
LDCM
HST
OSIRIS-REx
Euclid
May 08, 2014
STScI Lecture

29. Pre-Amplifier Block Diagram
Capacitor Feedback Design
Gain programmable by setting Cin and Cfb
Gain = Cin/Cfb
Low pass filter with programmable cutoff S3 S1 V1 V2 V3 V4 S4
Vref mid
bypass S5
SAR_En
SAR ADC output
LPF
Pipe_En
Pipeline ADC output S2
Cin
Cfb S6
Vpremidref
May 08, 2014
STScI Lecture

30. Preamp Drift and Mitigation
Data taken as 512 x 64 frames for efficiency, Gain = 4
σ= 52 ADU
Drift
kTC row noise
σ= 13.9 ADU
kTC removed (CCD mode)
σ= 2.6 ADU
May 08, 2014
STScI Lecture

31. Noise Reduction by Using Multiple ADC Channels
PreAmp inputs shorted to ground (lowest noise signal in order to be dominated by ADC noise)
PreAmp gain set to 4 (12 dB)
Noise measured by using multiple preamp and ADC channels in parallel (1, 2, 4, 6, and 8)
Noise reduces almost as the square root of the number of channels used
1 ADC
2 ADCs
4 ADCs
6 ADCs
8 ADCs
May 08, 2014
STScI Lecture

32. Bias Generator Block Diagram
SIDECAR has 20 Channels
Each Channel provides programmable voltage and current sources
Noise is caused mostly by buffer (1/f noise of MOS transistors)
Drive strength of buffer can be adjusted to modulate the bandwidth
Feedback compensation can be adjusted for stability
Buffer can be configured for single or dual stage operation
=> Tuning required for optimal noise performance
May 08, 2014
STScI Lecture

33. Bias Generator Noise Unfiltered Noise of Bias Output 1
Bias output 1 routed back into PreAmp
PreAmp gain set to 22 (27 dB)
Use 4 ADCs in parallel to reduce PreAmp & ADC noise
Noise on bias without filtering is about 35µV (11.6 ADU)
Noise can be reduced by RC filtering to less than 5µV
Unfiltered Noise of Bias Output 1
Bias noise as a function of RC filter time constant
Filtered Noise of Bias Output 1 (tRC = 360 ms)
PreAmp & ADC noise floor
May 08, 2014
STScI Lecture

34. Noise Power Spectrum of the Bias Outputs
FFT of temporal noise measurement with RC filter set to tRC= 3 µs
FFT of temporal noise measurement with RC filter set to tRC= 3 ms
May 08, 2014
STScI Lecture

35. Noise Power Spectrum of the Bias Outputs, Part 2
FFT of temporal noise measurement with RC filter set to tRC= 360ms
FFT of temporal noise measurement with grounded PreAmp inputs (i.e. noise floor)
May 08, 2014
STScI Lecture

36. Analog-to-Digital Conversion
Quantization noise of an ADC is
(1/√12) Least Significant Bit = LSB
Typically set gain of amplifier chain so that quantization noise is much less than readout noise. If readout noise is 4 electrons, set gain so that LSB equals ~2 electrons
16 bit ADC is most commonly used in astronomy. At ~2 electrons per ADU (analog to digital unit), or LSB, full well of a 16 bit ADC will be ~130,000 electrons; good match to the typical full well of a CCD or Short-Wave IR detector of 100,000 electrons.
Highly exaggerated quantization noise
“Don’t do this at home”
May 08, 2014
STScI Lecture

37. Differential Non-Linearity (DNL)
DNL describes the distance of an ADC code from its adjacent code.
It is measured as a change in input voltage magnitude, and then converted to number of Least Significant Bits (LSBs).
DNL = (VD+1 – VD) / VLSB-Ideal – 1
Code 100 is increased
DNL = +1
Code 10 is reduced
DNL = -0.5
Code 10 is missing
DNL = -1
May 08, 2014
STScI Lecture

38. Integral Non-Linearity (INL)
INL describes the deviation of the ADC transfer function from a straight line
It can be computed as the integral of the DNL, and is expressed in LSB
INL = (VD – VZero) / VLSB-Ideal – D
May 08, 2014
STScI Lecture

39. 16-bit ADC Linearity DNL INL
DNL [ LSB ]
INL [ LSB ]
Output Code
Differential Non-Linearity: < ± 0.3 LSB
Integral Non-Linearity: < ± 0.2 LSB
Temporal Noise: 2.7 LSB
Output Code
May 08, 2014
STScI Lecture

40. ADC Linearity Pitfalls
Differential ADC is composed of 2 separate single-ended ADCs
If one of the two ADCs saturates before the second one does, the transfer slope changes by 2
Slope change
Slope change
Vcm off by 160 mV
Vcm off by 80 mV
Requires careful adjustment of the ADC reference and common mode voltages
Simultaneous optimal tuning for all channels does not exist due to component mismatch
Avoid lower and upper end of ADC for science
Optimal Vcm
May 08, 2014
STScI Lecture

41. 1/F Noise in NIRSpec/JWST
Traditional CDS
Optimal CDS
σCDS ~ 18 e- rms
σCDS ~ 8 e- rms
May 08, 2014
STScI Lecture

42. (using real pixels as reference)
IRS^2 Noise Reduction Mode Example: NIRSpec 1000s Dark Up-the-Ramp Signal
Improved Reference Sampling & Subtraction (IRS^2) is a method to utilized reference pixels in a more efficient way
In every output channel, read reference pixels from the top or bottom or rows in-between the regular science pixels (e.g. read 4 reference pixels every 16 science pixels)
Use Fourier analysis to determine the frequency-dependent correlation between signal and reference pixels, and subtract the reference pixel signal accordingly
IRS^2
(using real pixels as reference)
Nominal (no IRS^2)
IRS^2
May 08, 2014
STScI Lecture

43. ACS 1/f Noise Bias Frame without correction (superbias subtracted)
Bias Frame with correction
(superbias subtracted)
May 08, 2014
STScI Lecture

44. Conclusion Infrared Detectors (Image Sensors) Control ASICs
Hybrid design: Detector material bump-bonded to readout chip
Different detector materials possible
HgCdTe for astronomy: lowest dark current and adjustable bandgap
Flexible readout options like guide mode or single-pixel reset
Control ASICs
Provide all functions to operate the detector
Clocking, Biasing, A/D conversion
Single-chip solution in contrast to discrete electronics
Lower power, space, weight
Can run cryogenically (next to the cooled detector)
Performance Improvements desired (lower noise, no artifacts)
May 08, 2014
STScI Lecture