Suppose you were designing a digital camera,
and you wanted to extend its battery
life by turning off its big power-hungry
display screen whenever its users have
their eye up to the optical viewfinder. Or suppose you
were designing a notebook and you wanted a feature
that would turn the keyboard backlight on only when the user’s
hands were near the keyboard. Or suppose you were designing a
touchscreen phone and you wanted to deactivate the on-screen
buttons when users hold the phone up against their head.
Now suppose you could do that with a chip that adjusts screen
brightness for ambient lighting as well. That’s what you get with Capella Microsystems’ CM3612 proximity
and ambient-light sensor chip,
which integrates patented optical filters,
photodiodes, an analog-to-digital
converter (ADC), and an I2C interface
(Fig. 1).
Applied as part of the semiconductor
fabrication process, the company’s
patent-pending Filtron technology tops
the proximity sensor diode with an
830- to 880-nm infrared filter and the
ambient-light sensor diode with a 450-
to 650-nm optical band-pass filter.
By limiting the wavelengths impinging
on the ambient light sensor, Capella
Microsystems mimics the human eye’s brightness-sensing
mechanism.
When it’s used to deactivate touchscreen phones, the
proximity sensor function drives an integrated infrared emitter
diode. The chip then uses its infrared
detector to look for light reflected from the
user’s head.
The 12-bit ADC both provides a representation
of light intensity via the serial
interface and feeds a digital low-pass
filter that removes florescent light flicker.
The CM3612 operates on voltages from
2.6 to 3.7 V and draws 130 µA (typical).
The lower-cost CM3601 eliminates the
I2C interface and uses a digital-to-analog
converter (DAC) to output the ambient
light value as an analog signal.
The CM3612 and CM3601 come in
2.35- by 1.8- by 1-mm optical land-grid
array (OPLGA) packaging and are sampling now (Fig. 2).
In quan ti ties of 10,000, the CM3612 costs $1.50, and the
CM3601 costs $1.20.
DON TUITE
CAPELLA MICROSYSTEMS
www.capellamicro.com
