Apparatuses and methods that reduce mismatch errors associated with analog subtractions used for light sensing
First Claim
1. A light measurement apparatus, comprising:
- a first sensor that senses light and generates a first current indicative of the light sensed by the first sensor;
a second sensor that senses light and generates a second current indicative of the light sensed by the second sensor;
an analog circuit that subtracts the first current from the second current to produce a third current that is equal to the first current minus the second current +/−
an error resulting from a mismatch error associated with the analog circuit;
an analog-to-digital converter that converts the third current to a digitized version of the third current; and
a calibration circuit that produces an adjustment signal in dependence on the digitized version of the third current;
wherein the adjustment signal produced by the calibration circuit is used to reduce the mismatch error associated with the analog circuit that subtracts the first current from the second current to produce the third current.
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Accused Products
Abstract
A system and method for adaptive analog infrared subtraction during ambient light sensing is provided. The system employs a current mirror circuit to perform an analog subtraction of currents (IIR and IIR+AB) obtained from photodiodes. An ADC is employed to digitize the output signal from the current mirror and, the digitized signal is amplitude modulated at a chop frequency utilized by the current mirror. Further, a digital filer is employed to generate an adjustment signal by filtering the modulated signal and the gain of the current mirror is calibrated by employing the adjustment signal. Moreover, as the adjustment signal converges to a value indicative of the mismatch error of the current mirror, the output signal of the current mirror provides an accurate value of ambient light incident on the photodiode.
20 Citations
19 Claims
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1. A light measurement apparatus, comprising:
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a first sensor that senses light and generates a first current indicative of the light sensed by the first sensor; a second sensor that senses light and generates a second current indicative of the light sensed by the second sensor; an analog circuit that subtracts the first current from the second current to produce a third current that is equal to the first current minus the second current +/−
an error resulting from a mismatch error associated with the analog circuit;an analog-to-digital converter that converts the third current to a digitized version of the third current; and a calibration circuit that produces an adjustment signal in dependence on the digitized version of the third current; wherein the adjustment signal produced by the calibration circuit is used to reduce the mismatch error associated with the analog circuit that subtracts the first current from the second current to produce the third current. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A method comprising:
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generating a first current indicative of an amount of a first sensed light; generating a second current indicative of an amount of a second sensed light; subtracting the first current from the second current using an analog circuit to produce a third current that is equal to the first current minus the second current +/−
an error resulting from a mismatch error associated with the analog circuit;converting the third current to a digitized version of the third current producing an adjustment signal in dependence on the digitized version of the third current; and adjusting a gain of the analog circuit, in dependence on the adjustment signal, to reduce the mismatch error associated with the analog circuit. - View Dependent Claims (15)
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16. An apparatus comprising:
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an analog current subtraction circuit including a current mirror circuit for generating an analog output signal based on a subtraction of a first current from a second current, wherein the first current is indicative of an amount of a sensed infrared (IR) light, the second current is indicative of a sum of an amount of sensed IR and an amount of sensed ambient visible light, and the analog output signal is equal to the first current minus the second current +/−
an error resulting from a mismatch error associated with the analog current subtraction circuit;an analog-to-digital convertor (ADC) for converting the analog output signal to a digital output signal; and a mismatch correction circuit for generating, in dependence on the digital output signal, an adjustment signal for adjusting a gain of the current mirror circuit to reduce the error in the analog output signal resulting from the mismatch error associated with the analog current subtraction circuit. - View Dependent Claims (17, 18, 19)
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Specification