Light source frequency detection circuit for image sensor
AssigneeOmniVision Technologies, Inc.
InventorsTiejun Dai, Jingzhou Zhang, Liping Deng
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Abstract
An apparatus for measuring the power frequency of a light source includes a photo-sensor, a modulator, and a logic unit. The photo-sensor generates an electrical signal that is responsive to light incident thereon from the light source. The modulator generates a modulated signal based on the electrical signal that toggles at a rate substantially proportional to the power frequency of the light source. The logic unit is coupled to receive the modulated signal and determine its toggling frequency.
Claims18
An apparatus for determining a power frequency of a light source, the apparatus comprising:
- a photo-sensor coupled to generate an electrical signal responsive to light incident thereon;
- a modulator circuit coupled to the photo-sensor to generate a modulated signal based on the electrical signal that toggles at a rate substantially proportional to the power frequency of the light source;
- and
- a logic unit coupled to the modulator circuit to determine a toggling frequency of the modulated signal and to generate a frequency select signal indicating the power frequency of the light source,
- wherein the modulator circuit comprises:
- a comparator including first and second comparator inputs and a comparator output, the first comparator input coupled to the photo-sensor and the second comparator input coupled to receive a reference signal;
- and
- a charging source coupled to selectively charge the first comparator input in response to the comparator output.
A method for determining a power frequency of a light source, comprising:
- generating an electrical signal responsive to light emitted from the light source and impinging upon a photo-sensor;
- generating a modulation signal toggling at a rate substantially proportional to the power frequency of the light, wherein generating the modulation signal includes:
- coupling the electrical signal to a circuit node;
- comparing a voltage of the circuit node to a reference voltage;
- toggling the modulation signal based on the comparing;
- latching the modulation signal synchronized to a clock source;
- and
- selectively charging or discharging the circuit node responsive to the modulation signal;
- and
- determining the power frequency of the light based at least in part upon the modulation signal.
An imaging system, comprising:
- a pixel array for capturing an image;
- a photo-sensor responsive to light incident thereon;
- a modulator circuit coupled to the photo-sensor to generate a modulated signal responsive to the light incident on the photo-sensor;
- and
- a logic unit coupled to the modulator circuit to receive the modulated signal and to determine a power frequency of the light incident on the photo-sensor based on the modulated signal, the logic unit further coupled to generate a frequency select signal indicating the power frequency of the light, wherein at least one operating characteristic of the pixel array is adjustable responsive to the frequency select signal,
- wherein the modulator circuit comprises:
- a comparator including first and second comparator inputs and a comparator output, the first comparator input coupled to the photo-sensor and the second comparator input coupled to receive a reference signal;
- a latch including a data input coupled to the comparator output and a data output;
- and
- a charging source coupled to selectively charge the first comparator input in response to the data output of the latch.
Dependencies are inferred from the claim text.