Sun Sensor on a Chip – ESA MPD 2010
Werner Ogiers – CMOSIS – Antwerp (B)
© copyright 2010 – CMOSIS nv
Project Background
• Sensor on a Chip study (ESA 20252/06/NL/JA)
– Selex Galileo prime
– feasibility of single-chip Star Tracker and Sun Sensor
• ESA Avionics Workshop 2007
– confirms market for micro-miniature, robust, versatile,
high-accuracy digital sun sensor
• ESA call
– “Digital Sun Sensor on a Chip Prototype Design and
Manufacture”
– ► ESA 21835/08/NL/ST (S.P.Airey, TEC-ECC)
– potential follow-up for EQM/FM
© copyright 2010 – CMOSIS nv
2
Contract SoW
• To design a highly miniaturised, plug and play, medium to high accuracy digital sun
sensor suitable for use on all classes of mission from nano s/c (<10Kg) to GEO
telecoms (18year lifetime) and planetary rovers (e.g. high dust environment).
• To demonstrate, via the production and testing of prototype hardware, the feasibility,
characteristics and performances of a medium to high accuracy highly miniaturised
digital sun sensor.
dimensions
mass
lifetime
SEU, LU
supply
power
sun position update rate
accuracy
interface
user interaction
© copyright 2010 – CMOSIS nv
40 x 40 x 30
60
18
immune
5
300
2 - 10
0.05
SpaceWire, UART
none
3
mm
g
years GEO
V nominal
mW peak
Hz
degrees, over FOV
Project team
• Selex Galileo (I)
– prime
– instrument design
• BAE Systems (UK)
– optics
• THAS (F)
– client side (S/C)
• CMOSIS
– sensor chip design
© copyright 2010 – CMOSIS nv
4
And now for something completely different ...
• We don’t want to make a single-chip
SUN SENSOR
• Long-term, we want a single-chip highperformance autonomous STAR TRACKER
• The work starts here. After all, the sun is a star
too ...
© copyright 2010 – CMOSIS nv
5
A Micro-Miniature STR?
clock
oscillator
4Mb NVM
(software, star
catalogue)
1Mb RAM
POR
Readout control
APS Image
Sensor + ADC
μProcessor
(LEON)
Image
processing
3.3V
regulator
© copyright 2010 – CMOSIS nv
1.8V
regulator
6
SpaceWire /
LVDS
3.3V
regulator
quaternions
A Micro-Miniature Sun Sensor?
clock
oscillator
POR
Readout control
APS Image
Sensor + ADC
Image
processing
3.3V
regulator
© copyright 2010 – CMOSIS nv
Tracker State
Machine
1.8V
regulator
7
SpaceWire /
LVDS
3.3V
regulator
(X,Y) or (α,β)
Overview
• Quick overview of the chip
• Three particular challenges
– CMOS process selection & IP
– Optical performance
– Power consumption
• Layout, present status
© copyright 2010 – CMOSIS nv
8
looks at sky
identifies sun
tracks sun
centroid to high
accuracy
– (X,Y) to AOCS
• System links
Y Decoders
–
–
–
–
3.3V
Reg
Bias Generators
• Digital camera
Analogue IO (test only)
SSoC chip diagram
POR
512 Column Amps
Temp.
Sensor
512 Column ADCs (10b)
X Multiplexer
Readout Sequencer
Pixel and Object
Processing
SpaceWire / UART
TC/TM Interface
Sun Tracker State
Machine
1.8V
Reg
– 5V supply
– TC/TM interface
© copyright 2010 – CMOSIS nv
512 x 512 Pixel Array
(10 μm)
OSC
3.3V
Reg
9
Supply
IO
Digital IO (LVDS)
SSoC operating modes
X
X
FPA
Y
FPA
Y
1. Acquisition Mode
1. Full-frame images (512x512 pixels) @ 5 Hz
2. Search for the sun
© copyright 2010 – CMOSIS nv
10
SSoC operating modes (2)
X
FPA
Y
FPA
Y
1. Tracking Mode
1. Windowed images (80 x 80) @ 10 – 60 Hz
1. Track while spinning: 90°/s up to 600°/s
2. Centroid: 1/100 pixel pitch accuracy ► 0.05° in 128° FOV
© copyright 2010 – CMOSIS nv
11
Sun detection (the fun bit)
1. Reject singular bright/dark pixels
1. = sensor defects
2. = SEU streaks
2. 2D clustering of bright pixels
1. grow potential sun cluster
2. reject too small, too large
3. 1..4 potential suns concurrently
1. pick the one closest to last-known sun position
2. export sun position as 16-bit coordinates (X,Y)
© copyright 2010 – CMOSIS nv
12
Sun detection
1. Reject singular bright/dark pixels
1. = sensor defects
2. = SEU streaks
2. 2D clustering of bright pixels
1. grow potential sun cluster
2. reject too small, too large
3. 1..4 potential suns concurrently
1. pick the one closest to last-known sun position
2. export sun position as 16-bit coordinates (X,Y)
© copyright 2010 – CMOSIS nv
13
Sun detection
1. Reject singular bright/dark pixels
1. = sensor defects
2. = SEU streaks
2. 2D clustering of bright pixels
1. grow potential sun cluster
2. reject too small, too large
3. 1..4 potential suns concurrently
1. pick the one closest to last-known sun position
2. export sun position as 16-bit coordinates (X,Y)
© copyright 2010 – CMOSIS nv
14
Sun detection
1. Reject singular bright/dark pixels
1. = sensor defects
2. = SEU streaks
2. 2D clustering of bright pixels
1. grow potential sun cluster
2. reject too small, too large
3. 1..4 potential suns concurrently
1. pick the one closest to last-known sun position
2. export sun position as 16-bit coordinates (X,Y)
© copyright 2010 – CMOSIS nv
15
Challenge 1: CMOS process selection
• Circuit density, power
– ►180 n
• Radiation hardness
– FASTRAD simulation at system level
• chip parts > 300 krad
• commercial logic libs risky
– IMEC DARE libs ► UMC 180n Logic
© copyright 2010 – CMOSIS nv
16
Challenge 1: CMOS process selection (2)
• Electro-optical performance
– Pinned photodiode: lowest dark current & noise
• dark current is next barrier in STR performance
• each pixel ~ single-cell CCD
• ►dedicated CMOS Image Sensor process (CIS)
– Old saying ‘APS = commodity CMOS’ is broken!
• UMC 180n CIS ≠ 180 nm Logic
– thinner stack (parasitics!), only 4 metals, ...
– DARE libs not compatible
• Noordwijk, we have a problem ...
© copyright 2010 – CMOSIS nv
17
Who DAREs wins
• A Miracle ...
– ESA agreed CCN to DARE90 (20896/07/NL/JD)
• Redesign selected IO cells for UMC 180 CIS
• Recharacterise all core cells
• Additional cells & functions (mask-programmable flipflop, LVDS power-down)
– IMEC initiated work
• well before contracts signed
– IMEC finished work
• almost before libs were needed (a big THANK YOU!)
• Problem remains for space Image Sensor SoC:
– most interesting IP is NOT compatible with best process
© copyright 2010 – CMOSIS nv
18
Challenge 2: optical performance
• Pinned Photo Diode pixel
– part science, part art
• Standard development flow
– test chip
– 100s of pixel variants, pick the best one
• Now
– first time use of UMC process
– no time, budget for test chip
• partial test chip in ‘similar’ TSMC process
• Risky business!
© copyright 2010 – CMOSIS nv
19
Challenge 3: Power
• Supply = 5V from S/C secondary bus
– peaks up to 7V <> 180nm process tolerates 3.5V
– cascoded linear regulators, tolerant to ... 5.5V
• STR will need DC/DC for 1.8V logic
• Power optimisation
– 99% of service life in tracking mode
• 20 ms capture, 80 ms idle
– Analogue: unclocked when idle
– Logic: data-driven automatic clock gating
• dark pixel ► clocks OFF
© copyright 2010 – CMOSIS nv
20
Clocks
ON
Power (2)
• Acquisition Mode (5Hz, full image)
– 240 mW @ 5V
• Tracking Mode (10Hz, 80x80 window)
– 170mW @ 5V
• BUT ...
– 93 mW in SpaceWire LVDS drivers
– 50% of chip ( = system!) power in Tracking Mode!!!
• Wouldn’t it be nice if someone sat down and
designed low-power LVDS for UMC 180nm?
© copyright 2010 – CMOSIS nv
21
Layout
• Large die
– 11 x 11 mm
– pixel array ~central
• wastes Si
– few power/ground pads
– large metal rings
• low-R for ESD
– floorplan = interface to
optics
© copyright 2010 – CMOSIS nv
Logic
512 x 512
pixels
512 ADCs
22
Layout (2)
• Immersed optics
– glass die with pinhole bonded onto
silicon die
– brings radiation shielding
– MEMS stack must not impede
wire bond tool
• few, spaced IO pad cells
– prototyped on LCMS sensor
© copyright 2010 – CMOSIS nv
23
Timeline
• February 2009: initiated project
– Requirements analysis
– Architectural design
– Algorithm (re)development for robustness
• May 2009: detailed design
– initially 1 jr analogue designer, 1 sr logic
– team grew, company too (+100%)
• November 2009: transfer to IMEC for back-end
– synthesis, clock gating, ATPG, layout
• March 2010: tapeout
© copyright 2010 – CMOSIS nv
24
Timeline (2)
• 13 months
– Longer than planned, but still faster than LCMS (FillFactory)
• Tempting Murphy
– First-time use of UMC process / foundry
• Critical for pixel development!
• January 2010: UMC offered foundry process
experiments / optimisation
– ► setup delayed tape out
– ► partially offsets lack of pixel test chip
– First-time use of ported core and IO cell libs + debug
• Annoying tool problems
• Devised new ESD strategy
© copyright 2010 – CMOSIS nv
25
Conclusions
• System on Chip Sun Sensor
– evaluate through 2010 (inc. radiation)
– EQM / FM in 2011?
• Step towards SoC Star Trackers
–
–
–
–
–
DARE CMOS Image Sensor logic libs
Pinned diode pixels with very high performance
IP: regulators, POR, OSC, ...
Low power techniques
CIS process supply voltage tolerance
© copyright 2010 – CMOSIS nv
26
THANK YOU
Any questions?
© copyright 2010 – CMOSIS nv
© copyright 2010 – CMOSIS nv
28