Patent ID: 8692200
Filing Date: 2014-04-08
Classification: G01J

Abstract:
1. An optical proximity sensor, comprising: an infrared light emitter configured to emit AC pulses of infrared light, the infrared light emitter further being configured to emit no or low levels of infrared light in-between AC pulses; a light detector configured to detect ambient light DC signals and infrared light AC pulses emitted by the light emitter and reflected from an object to be detected towards the light detector, and a differential integrator circuit operably connected to the light detector and configured to receive output signals therefrom representative of the ambient light DC signals and the reflected infrared light AC pulses; wherein the differential integrator circuit comprises a differential amplifier configured to receive first input signals from the light detector representative of the ambient light DC signals during first periods of time occurring in-between the pulses at a first input of the differential amplifier and second input signals representative of a combination of the ambient light DC signals and the reflected infrared light AC pulses during second periods of time occurring during the pulses at a second input of the differential amplifier, the differential integrator circuit further comprising a common mode feedback circuit connected to first and second outputs of the differential amplifier, the differential amplifier and differential integrator circuit being configured to provide first and second analog output signals representative of positive and negative integrated reflected infrared light AC pulses, respectively, the first and second analog output signals having the ambient light DC signals cancelled therefrom, wherein the differential integrator circuit comprises a first capacitor on a first current path from the first input of the differential amplifier to a first output of the differential amplifier that provides the first analog output signals and a second capacitor on a second current path from the second input of the differential amplifier to a second output of the differential amplifier that provides the second analog output signals and wherein the differential integrator circuit comprises first and second reset switches connected to the first capacitor and third and fourth reset switches connected to the second capacitor, the first and third reset switches being connected to discharge the first and second capacitors at an end of a measurement cycle, the second reset switch being connected to set the first input of the differential amplifier to a common mode voltage during the second periods, the fourth reset switch being connected to set the second input of the differential amplifier to the common mode voltage during the first periods.