Image Sensor Technologies
description
Transcript of Image Sensor Technologies
Image Sensor Technologies
Chris SolteszSSE DeluxeSony 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
BLUE
GREEN
RED
R
G B
Y
C
MWHITE
1
111 1
1111
111
000
0000
0000
0
Dichroic Prism
White Light
Blue Imager
Green Imager
Red Imager
Additive Color
Image Sensor Technologies
Image Sensor Technologies
What is the difference between CCD & CMOS imagers?a) Generate and Collect Charge
b) Measure Charge and turn into voltage or current
c) Output the signal
d) Transfer MechanismThe difference is in the strategies and mechanisms developed tocarry out those functions.
Light-to-charge Conversion
ChargeAccumulation
Photo Sensor (Light-sensitive Region) of a Pixel
Charge Transfer
Vertical and Horizontal CCD
Amplifier behind Horizontal CCD
Charge-to-voltage Conversion /Amplification
Signal Wire (Micro Wire)
Voltage Transfer
Charge-to-voltage Conversion /Amplification
CCD Image Sensor
CMOS Image Sensor
Amplifier within Pixel
Mechanism Differences
V
QC VCQ or
Capacitance Equation
C = Capacitance
Q = Charge
V = Voltage
Light
Charge (Electrons)
Photo Sensor (b) (Light-sensitive
Region)
Vertical CCD (c)
Horizontal CCD (d)Amplifier
(x)
Pixel
(a)
Output
CCD Image Sensor
Photo Sensor (b) (Light-sensitive Region)
Light
Charge
Signal
Amplifier
(y)Pixel
(a)
Column Signal Wire (f) (Micro Wire)
Pixel-select Switch (e)
ONON ON
Output ON
Column
Circuit (h)Row Signal Wire (i) (Micro Wire)
Column-select Switch
(g)
Pixel Row (j)
CMOS Image Sensor
Basic Mechanism of CCD Image Sensors
Light
Charge (Electrons)
Photo Sensor (b) (Light-sensitive
Region)
Vertical CCD (c)
Horizontal CCD (d)Amplifier
(x)
Pixel
(a)
Output
CCD Image Sensor
Light
Photo Sensor
Gate
Charge (Electrons)
Gate Opens
Vertical CCD
Charge (Electrons)
Charge Transfer- Photo Sensor to Vertical CCD
The transfer of charge in a CCD is similar to a bucket-brigade moving water
CCD CCDCCDCCD
Charge
Charge Transfer
ChargeCharge
Charge
Gate GateOutput Gate Gate
Horizontal CCD
Floating Diffusion (FD)
Amplifier of CCD Image Sensor
Charge
Micro Wire
Voltage Generated on Surface of FD
Amplifier
Output
Basic Mechanism of CMOS Image Sensors
CMOS Image Sensor
Photodiode Active-Pixel Architecture (APS) Actual Photodiode Active-Pixel Architecture
CMOS Image Sensor
Photo Sensor (b) (Light-sensitive Region)
Light
Charge
Signal
Amplifier
(y)Pixel
(a)
Column Signal Wire (f) (Micro Wire)
Pixel-select Switch (e)
ONON ON
Output
ON
Column
Circuit (h)Row Signal Wire (i) (Micro Wire)
Column-select Switch
(g)
Pixel Row (j)
CMOS Image Sensor
High
0 V
Vo
ltag
e
Surface Voltage
Photo Sensor
Light
Surface Voltage to Amplifier
High
0 V
Vo
ltag
e
Surface Voltage
Photo Sensor
Surface Voltage to Amplifier
When Charge is NOT Accumulated in Photo Sensor
When Charge is Accumulated in Photo Sensor
Fig. A Fig. B
Charge
Voltage Detection
0 V
Amplified Voltage
High
V1
Gate
Current
Surface Voltage from Photo Sensor
When Charge is NOT Accumulated in Photo Sensor
0 V
Amplified Voltage
High
V2
V1
Surface Voltage from Photo Sensor
Gate Lifts
Signal Voltage
When Charge is Accumulated in Photo Sensor
Fig. C Fig. D
Voltage Detection
APS Block Diagram
CCD & APS Performance Improvements
CCD Image Sensor with 2-channel Horizontal CCDs
Light
Charge (Electrons)
Photo Sensor (Light-sensitive Area)
Vertical CCD
Horizontal CCD 2
Amplifier 1
Pixel
Channel 1
Channel 2
Horizontal CCD 1
Amplifier 2
Output
CMOS Image Sensor with 3-channel Outputs
Column Signal Wire (Micro Wire)
Photo Sensor (Light-sensitive Region)
Light
Charge
Signal
AmplifierPixel
Pixel-select Switch
ONON ON
Column-select Switch
Channel 1
Channel 3
Channel 2ON
Row Signal Wire (Micro Wire)ON
ON
Column Circuit
Output
Technologies Used to Improve Performance of Image Sensors
Signal Charge
HAL
Signal Charge
Free Electron
Conventional Photo Sensor
Buried-type Photo Sensor
Free Electron
P+N
P+N N N
P+
Photo Sensor
Read-out Gate
Floating Diffusion (FD)
FD Reset Gate
FD Reset Drain
Amplifier
Pixel-select Switch
N N
P-type Si (Substrate)
P+ (HAL)
Gate Gate
Gate
Gate
Drain Drain
Signal Wire
HAD-type CMOS Image Sensor
Source
SiO2
Poly-Si
Micro Condensing Lens
CCD SensorStructure
On-chipMicro-lens
Hyper HAD CCD Power HAD CCD
Micro Condensing Lens
Power HAD EX ImagerPerformance Improvement With New CCD construction
Improvement of Smear with thinner insulation membrane
Power HAD CCD camera : -125dB (Typical)
Power HAD EX CCD camera : -140dB (Typical)
Fig.-1 Power HAD CCD Sensor Construction
Poly Si
V-register
On-Chip-Micro lens
Poly Si
Sensor V-register
Fig.-2 New CCD Sensor Construction
Internal Lens
On-Chip-Micro lens
Sensor
Photo-Shieldingfilm
Photo-Shieldingfilm
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