Maxim has introduced a digital ambient light sensor that allows for incandescent and fluorescent illumination, and it senses proximity using infra-red.
Called MAX44000 and made on a BiCMOS process, the 2x2x0.6mm IC includes three optical sensors and two ADCs.
Two of the photodiodes and an optical filter are used together to mimic the optical response of the human eye in a variety of spectral environments with a 0.03 to 65,535 lux dynamic range.
There are practical difficul¬ties in trying to reproduce the ideal photopic curve in a small cost-efficient package," said Maxim. "The IC instead uses two different types of photodiodes, a green and an infrared, each of which is amplified and subtracted on-chip with suitable gain coefficients so that the most extreme light sources - fluo¬rescent and incandescent - are well matched to a com¬mercial luminance lux meter."
Separate user-programmable green and IR chan¬nel gain trim registers allow the sensor to be used under dark or coloured glass.
Proximity detection uses the third photodiode, which is also infra-red, and an IR LED pulsed by the chip.
Pulsing cuts power consumption and allows the circuit to reject ambient illumination.
"When a smartphone is brought up to a user's face, the touch screen must be shut off to prevent inadvertent touches that may disrupt the call," said the firm. "Thus a proximity sensor is crucial. Once a sensed signal is received, it is run through a front-end circuit to reject ambient infra-red and sent to an ADC."
Operation is from 1.7-3.6V and the chip consumes 5?A when only the ambient light sensor is enabled, and both chip and LED together can draw as little as 11µA (time averaged) when detecting proximity if the programmable LED current is set low. 70µA is typical if the LED is set for 100mA pulses.
Applications are expected with touch-screens in phones and portable devices, as well as in industrial and for presence detection.
