Apparatus and method for reducing noise in fingerprint sensing circuits

• US 8,787,632 B2
• Filed: 08/13/2013
• Issued: 07/22/2014
• Est. Priority Date: 04/04/2008
• Status: Active Grant

• Current Assignee: Synaptics Incorporated
• Original Assignee: Synaptics Incorporated
• Inventors: Dean, Gregory Lewis, Erhart, Richard Alexander, Jandu, Jaswinder, Thompson, Erik Jonathon
• Primary Examiner(s): Werner, Brian P
• Application Number:
  US13/965,978
• Publication Number:
  US 20140016838A1
• Time in Patent Office: 343 Days
• Field of Search: None
• US Class Current: 382/124
• CPC Class Codes: G06V 40/1306 non-optical, e.g. ultrasonic or capacitive sensing

Abstract

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.

Claims

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.

2. The biometric sensing apparatus of claim 1, wherein the biometric comprises an image of a fingerprint of a finger sampled by the biometric sensing apparatus.

3. The biometric sensing apparatus of claim 2 further comprising:

a transmitter element and a receiver element forming the image pixel at the image pixel location, the image pixel sensing time period defining a time during which the transmitter element and the receiver element for the image pixel at the image pixel location interact to form the analog response representative of the condition of the image pixel location being sampled during the image pixel sensing time period.

4. The biometric sensing apparatus of claim 1 further comprising:

the selected portion of the conversion time period being selected to allow noise induced by the digital component to substantially die out before the initiation of the image pixel sampling portion of the image pixel sensing time period.

5. The biometric sensing apparatus of claim 1 further comprising:

the selected portion of the conversion time being selected to activate the digital component while the analog to digital converter is in the beginning stages of converting the analog response to the digital response and lesser significant bits of the digital response are being determined by the analog to digital converter.

6. The biometric sensing apparatus of claim 1 further comprising:

the digital component comprising a processor processing the digital response.

7. The biometric sensing apparatus of claim 1 further comprising:

the digital component comprising a processor receiving the digital response.

8. The biometric sensing apparatus of claim 1 further comprising:

the digital component comprising a controller for the biometric sensing apparatus.

9. The biometric sensing apparatus of claim 1 further comprising:

the digital component comprising a controller for the analog to digital converter.

10. The biometric sensing apparatus of claim 1 further comprising:

the image pixel locations forming one of a one dimensional linear sensor array or a two dimensional grid sensor array.

11. The biometric sensing apparatus of claim 10 further comprising:

the one of the one dimensional linear sensor array or two dimensional grid sensor array being physically decoupled from a sensing apparatus integrated circuit controller.

12. The biometric sensing apparatus of claim 10 further comprising:

the one of the one dimensional linear sensor array or two dimensional grid sensor array being located off of a sensing apparatus integrated circuit controller die.

13. The biometric sensing apparatus of claim 1 further comprising:

the sensing apparatus being integrated with an access control mechanism for one of a security physical checkpoint, a portable computer, a personal data assistant, a cell phone, a gaming device, a navigation device, an information appliance or a data storage device.

14. 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.

15. The biometric sensing method of claim 14, wherein the biometric comprises an image of a fingerprint of a finger sampled by the biometric sensing method.

16. The biometric sensing method of claim 15 further comprising:

forming the image pixel at the image pixel location with a transmitter element and a receiver element, the image pixel sensing time period defining a time during which the transmitter element and the receiver element for the image pixel at the image pixel location interact to form the analog response representative of the condition of the image pixel location being sampled during the image pixel sensing time period.

17. The biometric sensing method of claim 14 further comprising:

the selected portion of the conversion time period being selected to allow noise induced by the digital component to substantially die out before the initiation of the image pixel sampling portion of the image pixel sensing time period.

18. The biometric sensing method of claim 14 further comprising:

the selected portion of the conversion time being selected to activate the digital component while the analog to digital converter is in the beginning stages of converting the analog response to the digital response and lesser significant bits of the digital response are being determined by the analog to digital converter.

19. The biometric sensing method of claim 14 further comprising:

the digital component comprising a processor processing the digital response.

20. The biometric sensing method of claim 14 further comprising:

the digital component comprising a processor receiving the digital response.

21. The biometric sensing method of claim 14 further comprising:

the digital component comprising a controller for the biometric sensing apparatus.

22. The biometric sensing method of claim 14 further comprising:

the digital component comprising a controller for the analog to digital converter.

23. The biometric sensing method of claim 14 further comprising:

the image pixel locations forming one of a one dimensional linear sensor array or a two dimensional grid sensor array.

24. The biometric sensing method of claim 23 further comprising:

the one of the one dimensional linear sensor array or two dimensional grid sensor array being physically decoupled from a sensing apparatus integrated circuit controller.

25. The biometric sensing method of claim 23 further comprising:

the one of the one dimensional linear sensor array or two dimensional grid sensor array being located off of a sensing apparatus integrated circuit controller die.

26. The biometric sensing method of claim 14 further comprising:

the sensing apparatus being integrated with an access control mechanism for one of a security physical checkpoint, a portable computer, a personal data assistant, a cell phone, a gaming device, a navigation device, an information appliance or a data storage device.

27. 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.