Camera Architecture and Microscopy Austin Blanco

How does a camera work? ► Light is converted to electrical charge. ► Charge is stored in potential wells, these are the “Pixels” on the camera. ► Energy collected in each pixel is digitized. ► Digital data is transferred to computer.

Photons Emitted from Sample Fluorphore or Transmitted Light Pixels in CCD Array

Pixel Architecture

Active Area Register Output Node A/D Converter Masked Area

Register Output Node A/D Converter Most microscope manufacturer cameras use this array! Zeiss Axiocam, Olympus DP Series, Nikon Qi/DS, Hamamatsu “Orca” Series, Photometrics “CoolSNAP” Series, Q-Imaging “Retiga” Series.

Back Thinning PE -Very Sensitive (<90% Quantum Efficiency) -Expensive Process (Chemicals etch silicon) -Can only be used on FT or Full Frame sensors (not Interlines) Barrier Potential Well N-Channel

Active CCD Area

Active Area EM Register Output Node A/D Converter Masked Area

EM Register – “Impact Ionization”

Color Methods ► Pixels are not able to discern colors. ► This limitation lends to three methods of “colorization” in order to build an image.

3 Shot Color CCD RGB Merge

3 CCD Color RGB Merge Light

Color Mosaic -Enables fast acquisition -Sacrifices intensity spatial resolution -Lowers Sensitivity -Only used on interline sensors

Pixel Size -Lower Spatial Resolution -Greater Dynamic Range -Faster -More Sensitive -Lower Spatial Resolution -Greater Dynamic Range -Faster -More Sensitive Larger pixels can hold more energy – Providing more dynamic range Smaller pixels hold less energy.

Resolution

Choosing the Best Camera Speed Sensitivity Resolution Back Thinned Frame Transfer EM CCD Color Mosaic Interline Monochrome

CMOS vs. CCD ► What is a “CMOS”  Complimentary Metal Oxide Semiconductor ► Designates an electrical conductor layout which is used for many applications:  Sensors  Memory  Transceivers  Data Converters

CMOS Architecture Active PixelsA/D Converters

CMOS Readout Column Select Row Select

Positive Aspects ► Both Sensor and electronics for control are manufactured on chip  Theoretically lower cost  Smaller complete package (no external boards required)  On chip processing is more powerful (color compositing) ► A/D at each pixel  Superior control of gain for color applications  Far greater speed potential than CCD’s at lower readout rates (lower A/D Noise per pixel)  Sub Arrays have much more power due to non-serial nature of architecture ► Rugged Design  Less soldier contacts means less potential for something to break

Negative Aspects ► Shuttering Methods  Nowhere for stored charge to go!  Commonly use “Rolling Shutter” to avoid problem ► Distorts moving objects  Full frame shuttering ► requires multiple transistors per pixel ► Solves rolling shutter drawbacks ► Reduces fill factor ► QE  Under 10um pixel size QE is lower for CMOS than CCD ► More on-active area parts reduces fill factor ► > 10um CCD & CMOS are equivalent in QE ► Dynamic Range  multiple layers of construction in CMOS design ► Offer photons the opportunity to bounce to neighboring pixels ► Causes image softening ► Reduces dynamic range (creates new noise source)  A/D variations between pixels increases noise factor

Integration Limits ► CMOS design changes  Require more work for integration into camera bodies  Slow concept to market (~18 months) ► CCD Design Changes  “Drop In” new CCD’s can be used in old designs  Faster turnaround means more profit now (~ 8 months)

Future of CMOS ► Potential for back thinning  Could avoid current problems with softening and lower QE  With back thinning would compete and possibly beat CCD’s for low light applications ► Specific Manufacturing Facilities  Originally CMOS were thought to be cheap in production. Ultimately specific foundries will be required for scientific grade chips. ► Cost will go up to or above CCD manufacture.

Conclusions ► CCDs and CMOS sensors fit our needs in complimentary ways:  CCDs for low light quantitative apps  CMOS for high resolution brightfield apps  CMOS for rugged environments  CCDs for speed apps  CMOS for small form factor  CCDs for high dynamic range brightfield ► CMOS sensors are a “disruptive technology”  Someday CMOS will eclipse and possibly replace CCDs, just like tape -> CD -> Mp3.  Reaching the performance level of CCDs will require CMOS prices to meet or exceed current CCD pricing, meaning a stable market for imaging apps in the future

Thank You! ► Austin Blanco ► Technical Instrument  Training on Imaging / Software  Custom Programming for Software  Consultation on Existing and New Systems ► ►