iam11_lecture04

This is done by electric elds in which a photocurrent

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: 11 12 13 14 15 16 17 18 19 20 • To make the electron-hole pairs usable for image sensing, the charges must be separated. This is done by electric fields in which a photocurrent results. • The photocurrent depends linearly on the light intensity over approx. 10 orders of magnitude. However, linearity may be lost in later steps. 21 22 23 24 25 26 27 28 Image Sensorics (5) 12 Semiconductor Photosensors 34 Charge Accumulation 56 • Photodiodes: charges move in electrical field of pre-charged capacity, reducing its voltage; decay in stored voltage is measured after exposition. 78 • Metal-Oxide Semiconductors (MOS): charges again move in electrical field but this time they are stored in “trap” formed by isolating metal oxide; charges can be accumulated and manipulated there. 11 12 9 10 13 14 15 16 17 18 19 20 21 22 23 24 Schematic drawings. Left: Photodiode. Right: MOS element. (both: Seitz, 1999) 25 26 27 28 Image Sensorics (6) 12 Semiconductor Photosensors 34 CCD Sensors 56 • Charge-coupled devices (CCD): one MOS element for each pixels 78 • Instead of addressing pixels individually by electrodes, accumulated charges are moved along lines by clock-switched electrical fields and read out sequentially at the end. 9 10 Full Frame CCD (Wikipedia) 11 12 13 14 15 16 • Various modifications of this basic read-out architecture exist. 17 18 19 20 21 22 23 24 Charge transport in CCD by step-wise switching of electrical fields. (Seitz 1999) 25 26 27 28 Image Sensorics (7) 12 Semiconductor Photosensors 34 Active Pixel Sensors 56 • Active pixel sensors integrate semiconductor-based photosensors (photodiodes or MOS elements) with further MOS/CMOS field-effect transistors in each pixel. 78 • Most important type: CMOS sensors (e.g. in expensive digital cameras) 11 12 • Amplification in each pixel instead of moving unamplified charges along rows reduces artifacts caused by interactions between pixels. 13 14 • Readout typically by an array logic: One input line per row, one output line per column; readout of a row is triggered via the input line. • Nonlinear responses can be electronically realised on pixel level. 9 10 15 16 17 18 19 20 21 22 23 24 25 26 27 28 Image Sensorics (8) Semiconductor Photosensors 12 34 High Dynamic Range Sensors 56 • Important case of nonlinear response: logarithmic response 78 • Used for high dynamic range CMOS (HDRC) sensors 9 10 • Makes brightness differences illumination independent (from the order of magnitude) 11 12 13 14 15 16 17 18 19 20 21 22 23 24 High dynamic range images acquired using a 64 × 64 pixel logarithmic sensor. (Seitz 1999) 25 26 27 28 Photographic Parameters 12 Photographic Parameters 34 Important Parameters for Cameras and Films 56 • Image diagonal. Larger sensors suffer less from noise (fixed pixel number). 78 • Focal length. For 24 × 36 mm image format 50 mm are normal focus. Shorter focal length: wi...
View Full Document

This note was uploaded on 07/09/2013 for the course SC 111 taught by Professor S during the Winter '12 term at Uni Saarland.

Ask a homework question - tutors are online