The
most recent that is poised to get rid of the TV camera ‘tube’ and the electron
beam scanning is the solid state image sensor. The device uses a charge
coupling principle for transfer of charge from one picture element to the next
with the help of a series of electrodes and is hence called a charge coupled
device (CCD) image sensor. This consist of Metal Oxide Semiconductor (MOS)
transistor family type silicon chip with an array of metal electrodes in group
of three electrodes that are provided with three-phase clock pulses for
shifting the charge packets in the silicon substrate, proportional to the
illumination at the surface.
most recent that is poised to get rid of the TV camera ‘tube’ and the electron
beam scanning is the solid state image sensor. The device uses a charge
coupling principle for transfer of charge from one picture element to the next
with the help of a series of electrodes and is hence called a charge coupled
device (CCD) image sensor. This consist of Metal Oxide Semiconductor (MOS)
transistor family type silicon chip with an array of metal electrodes in group
of three electrodes that are provided with three-phase clock pulses for
shifting the charge packets in the silicon substrate, proportional to the
illumination at the surface.
As
the optical image is focused on the front-face of the CCD silicon chip, a
corresponding charge pattern is formed in the substrate due to electrons
produced by the light collecting beneath the central electrodes that are the
most positive of the three sets of electrodes. The spot under each triplet set
of electrodes forms a picture element. Scanning is done by shifting the charge
packets by phasing the clock pulse to the three electrodes to be in succession.
The charge pattern is thus clocked out as a series of pulses of varying
amplitude according to the original optical image.
the optical image is focused on the front-face of the CCD silicon chip, a
corresponding charge pattern is formed in the substrate due to electrons
produced by the light collecting beneath the central electrodes that are the
most positive of the three sets of electrodes. The spot under each triplet set
of electrodes forms a picture element. Scanning is done by shifting the charge
packets by phasing the clock pulse to the three electrodes to be in succession.
The charge pattern is thus clocked out as a series of pulses of varying
amplitude according to the original optical image.
The
process of scanning takes place in two steps, an integrate period and a readout
period. During the integrate period, one set of electrodes is maintained at a
constant voltage creating a depletion region under each electrode.
Electron-hole pairs are generated within the depletion region under each
electrode. Electron-hole pairs generated within the depletion region are
collected under each electrode in the integrate period and are read out by the
phased clock pulses. The readout time is around 100µs short compared to the
integrate time of 1 to 10ms. This minimises smear effects due to changes in
illumination during readout. The process of line imaging can be extended to the
frame imaging system for forming a TV picture frame signal.
process of scanning takes place in two steps, an integrate period and a readout
period. During the integrate period, one set of electrodes is maintained at a
constant voltage creating a depletion region under each electrode.
Electron-hole pairs are generated within the depletion region under each
electrode. Electron-hole pairs generated within the depletion region are
collected under each electrode in the integrate period and are read out by the
phased clock pulses. The readout time is around 100µs short compared to the
integrate time of 1 to 10ms. This minimises smear effects due to changes in
illumination during readout. The process of line imaging can be extended to the
frame imaging system for forming a TV picture frame signal.
