Transcript document

Image Sensor
Technologies
Chris Soltesz
SSE Deluxe
Sony Electronics, Inc.
BPSD
Image Sensor
Technologies
An introductory guide to CCD
and CMOS imagers
Image Sensors

An image sensor is an electronic device that converts a
image (light) to an electric signal.

They’re used in digital cameras and other imaging devices.
Imagers are typically an array of charge-coupled devices (CCD)
or CMOS sensors such as active-pixel sensors (APS).
Color Principles
Electromagnetic Spectrum
Spectral Characteristics
Color Primaries
Color Primaries
R
Y
M
WHITE
G
C
B
BLUE
1
0
1
0
1
0
1
0
RED
1
1
0
0
1
1
0
0
GREEN
1
1
1
1
0
0
0
0
Dichroic Prism
Blue Imager
Green Imager
White Light
Red Imager
Additive Color
Image Sensor
Technologies
Image Sensor Technologies
What is the difference between
CCD & CMOS imagers?
a)
b)
c)
d)
Generate and Collect Charge
Measure Charge and turn into voltage or
current
Output
signal is in the
Thethe
difference
strategies
and mechanisms
Transfer
Mechanism
developed to
carry out those functions.
Mechanism Differences
CCD Image Sensor
Charge
Transfer
Vertical and
Horizontal CCD
Light-to-charge
Conversion
Capacitance Equation
Q
V
or
C = Capacitance
Q = Charge
V = Voltage
Amplifier behind
Horizontal CCD
Charge
Accumulation
Photo Sensor (Light-sensitive Region) of a Pixel
C
Charge-to-voltage
Conversion
/Amplification
Q  C V
Charge-to-voltage
Conversion
/Amplification
Amplifier
within Pixel
Voltage
Transfer
Signal Wire
(Micro Wire)
CMOS Image Sensor
CCD Image Sensor
Pixel
(a)
Light
Photo Sensor (b)
(Light-sensitive Region)
Charge
(Electrons)
Vertical CCD (c)
Output
Amplifier
(x)
Horizontal CCD (d)
CMOS Image Sensor
Pixel
Amplifier
Photo Sensor (b)
(a)
(y)
(Light-sensitive Region)
Light
Signal
ON
ON
Charge
O
N
Pixel-select Switch (e)
Pixel Row (j)
Column Signal Wire
(Micro Wire)
(f)
Column-select Switch
(g)
Column
Circuit (h)
Row Signal Wire (i)
(Micro Wire)
ON
Output
Basic Mechanism of
CCD Image Sensors
CCD Image Sensor
Pixel
(a)
Light
Photo Sensor (b)
(Light-sensitive Region)
Charge
(Electrons)
Vertical CCD (c)
Output
Amplifier
(x)
Horizontal CCD (d)
Charge Transfer- Photo Sensor to Vertical CCD
Light
Charge
(Electrons)
Photo Sensor
Gate Opens
Gate
Charge
(Electrons)
Vertical CCD
Charge Transfer
The transfer of charge in a CCD is similar to a bucket-brigade
moving water
CCD
Charge
CCD
CCD
CCD
Amplifier of CCD Image Sensor
Voltage
Generated on
Surface of FD
Horizontal CCD
Output
Output
Gate
Amplifier
Micro Wire
Charge
Floating Diffusion (FD)
Gate
Gate
Gate
Basic Mechanism of
CMOS Image Sensors
CMOS Image Sensor
Photodiode Active-Pixel Architecture (APS)
Actual Photodiode Active-Pixel Architecture
CMOS Image Sensor
CMOS Image Sensor
Pixel
Amplifier
Photo Sensor (b)
(a)
(y)
(Light-sensitive Region)
Light
Signal
ON
ON
Charge
O
N
Pixel-select Switch (e)
Pixel Row (j)
Column Signal Wire
(Micro Wire)
(f)
Column-select Switch
(g)
Column
Circuit (h)
Row Signal Wire (i)
(Micro Wire)
ON
Outpu
t
Voltage Detection
Fig. A When Charge is NOT Accumulated in
Photo Sensor
Surface Voltage
to Amplifier
Fig. B When Charge is Accumulated in
Photo Sensor
Surface Voltage
to Amplifier
Surface
Voltage
Surface
Voltage
0V
Voltage
Voltage
0V
Light
High
Photo Sensor
High
Charge
Photo Sensor
Voltage Detection
Fig. C When Charge is NOT Accumulated
in Photo Sensor
Surface Voltage
from Photo Sensor
Amplified
Voltage
Fig. D When Charge is Accumulated
in Photo Sensor
Amplified
Voltage
Surface Voltage
from Photo Sensor
0V
0V
V2
Current
Signal Voltage
V1
V1
High
Gate
Gate Lifts
High
APS Block Diagram
CCD & APS
Performance
Improvements
CCD Image Sensor with
2-channel Horizontal CCDs
Photo Sensor
(Light-sensitive Area)
Light
Pixel
Charge
(Electrons)
Vertical CCD
Output
Amplifier 1
Channel 1
Horizontal
CCD 1
Channel 2
Horizontal
CCD 2
Amplifier 2
CMOS Image Sensor with 3-channel Outputs
Pixel
Photo Sensor
(Light-sensitive Region)
Amplifier
Light
Signal
ON
ON
Charge
ON
Pixel-select Switch
Column-select Switch
Output
Channel 1
Channel 2
Channel 3
ON
Column
Circuit
Column Signal Wire
(Micro Wire)
ON
ON
Row Signal Wire
(Micro Wire)
Technologies Used to
Improve Performance of
Image Sensors
Buried-type
Photo Sensor
Conventional
Photo Sensor
Free
Electron
HAL
Free
Electron
Signal
Charge
Signal
Charge
HAD-type CMOS Image Sensor
Gate
Gate
Gate
Signal Wire
Poly-Si
Gate
Drain Drain
P+
P+ (HAL)
Source
P+
N
N
N
P+
N
N
SiO2
N
P-type Si
(Substrate)
Photo
Sensor
Readout
Gate
FD
Reset
Gate
Floating Diffusion (FD)
FD
Reset
Drain
Pixel-select
Switch
Amplifier
Micro Condensing Lens
Micro Condensing Lens
On-chip
Micro-lens
CCD Sensor
Structure
Hyper HAD CCD
Power HAD CCD
Power HAD EX Imager
Performance Improvement With New CCD construction
On-Chip-Micro lens
On-Chip-Micro lens
Internal Lens
Photo-Shielding
film
Photo-Shielding
film
Poly Si
Poly Si
Sensor
V-register
Sensor
Fig.-1 Power HAD CCD Sensor Construction
V-register
Fig.-2 New CCD Sensor Construction
Improvement of Smear with thinner insulation membrane
Power HAD CCD camera ：
Power HAD EX CCD camera
-125dB (Typical)
：
-140dB (Typical)
Thinner
Insulation
Film
Pros and Cons of
Image Sensors
Pros & Cons of Imagers
Feature Comparison
Feature
CCD
CMOS
Signal out of pixel
Electron packet
Voltage
Signal out of chip
Voltage (analog)
Bits (digital)
Signal out of camera
Bits (digital)
Bits (digital)
Fill factor
High
Moderate
Amplifier mismatch
N/A
Moderate
System Noise
Low
Moderate
System Complexity
High
Low
Sensor Complexity
Low
High
Camera components
Sensor + multiple support chips + lens
Sensor + lens possible, but additional support chips common
Relative R&D cost
Lower
Higher
Relative system cost
Depends on Application
Depends on Application
Pros & Cons of Imagers
Performance Comparison
Performance
CCD
CMOS
Responsivity
Moderate
Slightly better
Dynamic Range
High
Moderate
Uniformity
High
Low to Moderate
Uniform Shuttering
Fast, common
Poor
Uniformity
High
Low to Moderate
Speed
Moderate to High
Higher
Windowing
Limited
Extensive
Antiblooming
High to none
High
Biasing and Clocking
Multiple, higher voltage
Single, low-voltage
Pros & Cons of Imagers
Winding Path of
CMOS Development's
Initial Prediction for CMOS
Twist
Outcome
Equivalence to CCD in imaging
performance
Required much greater process adaptation and
deeper submicron lithography than initially
thought
High performance available in CMOS, but with
higher development cost than CCD
On-chip circuit integration
Longer development cycles, increased cost,
tradeoffs with noise, flexibility during operation
Greater integration in CMOS, but companion
chips still required for both CMOS and CCD
Reduced power consumption
Steady improvement in CCDs
Advantage for CMOS, but margin diminished
Reduced imaging subsystem size
Optics, companion chips and packaging are often
the dominant factors in imaging subsystem size
CCDs and CMOS comparable
Economies of scale from using
mainstream logic and memory
foundries
Extensive process development and optimization
required
CMOS imagers use legacy production lines with
highly adapted processes akin to CCD fabrication
Image Distortion with CMOS Camera
CMOS Camera