Apparatus and method for reducing noise in fingerprint sensing circuits

摘要

An apparatus for reducing noise in fingerprint sensing circuits is disclosed in one embodiment of the invention as including a fingerprint sensing area onto which a user can apply a fingerprint. An analog front end is coupled to the fingerprint sensing area and is configured to generate an analog response signal. An analog-to-digital converter (ADC) samples the analog response signal and converts the sample to a digital value, which may be received by a digital device such as a processor or CPU. To reduce the amount of the noise that is present in the analog response signal and therefore reflected in the digital value, the digital device may be shut down while the ADC is sampling the analog response signal.

主权项

1. A biometric sensing apparatus comprising:
an analog sensor having image pixel locations, each image pixel location sensed during a respective image pixel sensing time period, to provide an analog response representative of the condition of an image pixel at the image pixel location being sampled during the image pixel sensing time period; an analog to digital converter connected to the analog output of the image pixel at the image pixel location and configured to sample the analog response for the image pixel at the image pixel location during the respective image pixel sensing time period; a digital component having digital circuitry at least indirectly coupled to the analog to digital converter during at least a portion of the image pixel sensing time period; an analog to digital converter timing circuit configured to activate 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 during the 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 to activate 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; a digital component timing circuit configured to activate the digital component during a selected portion of the conversion time period and not to activate the digital component during the image pixel sampling time portion of the image pixel sensing time period.