CIE colour sensor chip is calibrated

AS7261 is a calibrated XYZ colour point sensor from AMS, intended for handheld colour analysers and calibration for paint colour matching, fluid colour analysis, display management and light metering.

AMS AS7261 block - CIE colour sensor chip is calibrated

It is part of a family of similar chips – scroll to the end for the other two.

Integrated silicon Gaussian interference filters are used, providing direct XYZ coordinates consistent with the CIE 1931 2° standard observer, in the case of the AS7261.

Additional mapping of XYZ coordinates to the x, y (Y) of the 2-dimensional colour gamut and scales of the CIE 1976 u’v’ coordinate system provide correlated colour temperature (CCT) measurements and colour point deviation from the black body curve for white in ∆u’v’ coordinates.

A Near-IR channel and LED drivers with programmable currents increase application flexibility, including support for electronic shutter applications.

“Its tri-stimulus XYZ colour sensing capability means, that it mimics the human eye’s response curve, represented by the CIE 1931 and CIE 1976 colour mapping systems,” said the firm. “The measurements of white light made by the AS7261 are typically accurate to ±0.002du’v’ on the CIE 1976 scale.”

Performance is maintained, according to AMS, thanks to the silicon filter set integrated on to the sensor die, which are resistant to temperature and ageing effects, and intelligence integrated into the sensor allows for calibration as part of the manufacturing process. “These in-line calibration processes often eliminate the need for end product manufacturers to calibrate each end-device on their own production line,” it claimed.

AMS AS7261 detail blockThere are six photo-diodes inside, filtered to be X Y Z C D and near-IR. A 16-bit ADC measures them. Control and spectral data access is through either I²C or serial UART.

Via the UART, the host microcontroller uses AT Commands  – the serial command interface interface borrowed from the ‘AT Command’ model used in early Hayes modems. I²C access is through a virtual register set.

There are two LED driver pins. One can be used to indicate when the flash memory is being programmed, or both LED driver pins can be used for electronic shutter applications which allows different
wavelength light sources to be used in the same system. Sink currents ca be set to 1, 2, 4 or 8mA on on pin and 12.5, 25, 50 or 100mA on the other.

Maximum operating current is 5mA from 3.3V.

AMS AS7261 opticOptics built into the 4.5 x 4.7mm LGA package deliver a ±20.5° field of view.

An evaluation board is available from the AMS on-line store.

Tennessee-based Variable has used the sensor in a colour identification device called Color Muse.

AS7261 is part of a family of chips.

AS7262 is similar, but with six visible channels, filtered at: 450, 500, 550, 570, 600 and 650nm, each with 40nm full-width half-max (FWHM).

AS7262 is similar, but with six near-IR channels at: 610, 680, 730, 760, 810 and 860, each with 20nm FWHM.

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