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Browse Prior Art Database

Active Pixel Battery Charger

IP.com Disclosure Number: IPCOM000118597D
Original Publication Date: 1997-Apr-01
Included in the Prior Art Database: 2005-Apr-01
Document File: 2 page(s) / 54K

Publishing Venue

IBM

Related People

Hook, T: AUTHOR [+2]

Abstract

Digital cameras require batteries to operate, which sometimes go dead at inopportune times. This disclosure uses the photo-current of active pixel sensors (or other solid-state imaging chip) to charge the batteries while in standby mode.

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Active Pixel

Battery

Charger

      Digital cameras require batteries to operate, which sometimes
go dead at inopportune times.  This disclosure uses the photo-current
of active pixel sensors (or other solid-state imaging chip) to charge
the batteries while in standby mode.

      Solid-state imaging chips (such as Charge-Coupled Devices
(CCDs) and active pixel sensors) can act as solar cells, since they
convert light energy into electrical energy.  The following discloses
a system which allows the chip to act as a battery charger when the
camera is not in use.

      With the addition of control logic and a Direct Current-Direct
Current (DC-DC) converter, power generated by the imaging chip may be
collected and boosted to supply charging current to the battery.  The
control logic is necessary to turn on all of the word lines and bit
switches in order to direct the current from all of the cells into a
single output.  The DC-DC converter is necessary because the voltage
output is generally limited to a single photodiode potential.  The
imager array typically has a common substrate node for all of the
cells.

The amount of power available may be calculated as follows for the
current typical application:
  o  Power to Earth's surface (AM1.5) = 844 W/m2
  o  Assumed efficiency of Si imager  = 5-10%
  o  Fill factor (w/ microlens)       = 35-60%
  o  1E6 pixels at 52 um2 each        =52E6 um2
  o  DC-DC converter at 90% efficiency = 0.9x
 ...