Apparatus and method for reducing noise in fingerprint sensing circuits

A method of sensing a biometric image comprising:

• sensing an analog response representative of a condition of an image pixel at an image pixel location by using an analog sensor having image pixel locations, each image pixel location being sensed during a respective image pixel sensing time period, to provide the analog response for the image pixel at the image pixel location being sampled during the image pixel sensing time period;
• sampling the analog response for the image pixel at the image pixel location during the respective image pixel sensing time period using an analog to digital converter connected to the analog output of the image pixel at the image pixel location;
• coupling a digital component having digital circuitry at least indirectly to the analog to digital converter during at least a portion of the image pixel sensing time period;
• activating conversion of a sampled analog response for a prior image pixel location sampled during a prior image pixel location sensing time period, in order to form a digital response for the prior image pixel location sampled duringthe prior image pixel sensing time period, during a conversion time period portion of the image pixel sensing time period at the same time as the analog to digital converter is receiving the analog output of the image pixel at the image pixel location, and activating sampling of the analog response for the image pixel location being sampled during an image pixel sampling time portion of the image pixel sensing time period, the sampling time portion of the image pixel sensing time period being selected to follow the conversion time period and to allow the analog response sampled during the image pixel sampling time portion of the image pixel sensing time period to have substantially reached steady state during the image pixel sensing time period;
• activating the digital component during a selected portion of the conversion time period and not activating the digital component during the image pixel sampling time portion of the image pixel sensing time period.

A tangible machine readable medium storing instructions that, when executed by a computing device cause the computing device to perform a method, the method comprising:

• sensing an analog response representative of a condition of an image pixel at an image pixel location by using an analog sensor having image pixel locations, each image pixel location being sensed during a respective image pixel sensing time period, to provide the analog response for the image pixel at the image pixel location being sampled during the image pixel sensing time period;
• sampling the analog response for the image pixel at the image pixel location during the respective image pixel sensing time period using an analog to digital converter connected to the analog output of the image pixel at the image pixel location;
• coupling a digital component having digital circuitry at least indirectly to the analog to digital converter during at least a portion of the image pixel sensing time period;
• activating conversion of a sampled analog response for a prior image pixel location sampled during a prior image pixel location sensing time period, in order to form a digital response for the prior image pixel location sampled duringthe prior image pixel sensing time, during a conversion time period portion of the image pixel sensing time period at the same time as the analog to digital converter is receiving the analog output of the image pixel at the image pixel location, and activating sampling of the analog response for the image pixel location being sampled during an image pixel sampling time portion of the image pixel sensing time period, the sampling time portion of the image pixel sensing time period being selected to follow the conversion time period and to allow the analog response sampled during the image pixel sampling time portion of the image pixel sensing time period to have substantially reached steady state during the image pixel sensing time period;
• activating the digital component during a selected portion of the conversion time period and not activating the digital component during the image pixel sampling time portion of the image pixel sensing time period.