• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

What are differences between CCDs used in scanners and CCDs used in cameras?

Status
Not open for further replies.

sara_s

New Member
What are differences between CCDs used in scanners and CCDs used in cameras? Do they have different sensitivity to light?

I have two electrical circuit for a CCD sensor used in scanner and a CCD sensor used in camera. the latest works even for lights far from the sensor, but the formest works only when a light source is sufficiently near to sensor. why?
 

Les Jones

Well-Known Member
Most Helpful Member
What you say is not true. The distance between the light source and the sensor depends on the optics (Lenses and mirrors.) between the light source and the sensor. The difference ia that the sensor used in a scanner is one dimensional. (A number of individual cells arranged in a straight line. A camera sensor is a 2 dimensional array of sensors. A scanner produces a 2 dimensional image as the sensor is moved with respect to the image. This normaly takes several seconds.

Les.
 

sara_s

New Member
thanks for your answer.
My CCD sensor (which used in scanner) is a linear and color one (RGB).
However I have this question:
What do we expect to see as a output of CCD when there are no optical system between light source and CCD?
Is there no output without optical system?!! Doesn't CCD indicate any sensitivity to light without optical system?!!

I have a non-zero output voltage on oscilloscope only when the light source (typical lamp 100watt or laser) is so near to CCD.
this output will be zero (dark) as soon as moving the source far from CCD.
Do this CCDs works for specific distance between them and sorce or
Should i use some sorce such as xenon lamp (similar to scanners)
to see the non-zero output voltage for any distance between sorce and CCD?
 

spec

Well-Known Member
Most Helpful Member
What are differences between CCDs used in scanners and CCDs used in cameras? Do they have different sensitivity to light?
Yes: big time. A camera has a vastly harder job to do than a scanner. Camera manufacturers spend millions trying to increase the ISO rating (sensitivity) of their cameras. CMOS arrays are mainly used now on high end cameras.

spec
 

Tony Stewart

Well-Known Member
Most Helpful Member
Since gain of CCD depends on load R for light current to voltage in order to increase Bandwidth of pixel light they must reduce RC integration time with much lower R results in very low voltage= I*R unless much brighter LUX levels such as scanners, with one linear capture at a time then increment, settle repeat using microstepping.

Camera may have 480 to 4k pixels vertical but capture all at once(unless sliding aperture) but scanners might have 100x as many pixels in max resolution raw image and need to step and settle between increments so much slower mechanism needs much faster capture since it is not capturing light all the time.
 
Last edited:

sara_s

New Member
Thanks. According to the CCD's data sheet, response or sensitivity of this sensor isn't high.
Perhaps it needs some special optical system and a source with high intensity
such as xenon lamp (which used in scanners) to get better results.

I have another related problem:

My work is based on FPGA and VHDL. analog output of CCD sensor ,observed on oscilloscope screen, has below typical shape. but it acts reversely. that is, the differences between the reference level and data level will be max while dark source and it will be min (near to zero) while max of intensity of light source!!! I don't know why it act reversely...
Moreover, after the converting of analog to digital, the observed output of AFE is noisy in both states of dark source and light source.
can you help me?
 

Attachments

Tony Stewart

Well-Known Member
Most Helpful Member
In TV, Black level is always closest to reference after negative sync tip with positive 100% IRE white

Here you show the same except everything is inverted. This is how TV carrier was modulated in old analog days with sync tip and black for the strongest carrier
 
Status
Not open for further replies.

Latest threads

EE World Online Articles

Loading
Top