Optical-fingerprint detection system
A method of temperature compensation in an optical-fingerprint detection system includes acquiring a first reading associated with one or more pixels of an array. The first reading is a baseline reading. The method further includes acquiring a second reading associated with the one or more pixels of the array. The second reading includes the baseline plus a signal. Producing a temperature compensated signal reading by subtracting the first reading from the second reading. The array is an optical-fingerprint array, and each pixel of the array is coupled to a readout circuit via a pixel switch. The method includes row-based and frame-based schemes and a blind pixel scheme. Readout circuit improvements including multiplexed analog front-end (AFE), charge magnifier with column charge offset compensation and a low-noise gate driver circuit are provided.
1. A method of temperature compensation in an optical-fingerprint detection system, the method comprising:
acquiring, by using a readout circuit, a first reading associated with at least one pixel of an array, wherein the first reading includes temperature-dependent noise components;
acquiring, by using the readout circuit, a second reading associated with the at least one pixel of the array, wherein the second reading includes both the temperature-dependent noise components and a signal reading; and
producing a temperature compensated signal reading corresponding to the signal reading by subtracting the first reading from the second reading,
wherein the array comprises an optical-fingerprint array, the at least one pixel of the array is coupled to the readout circuit via at least one pixel switch, and the first reading is a baseline reading.
2. The method of claim 1 , wherein a temperature compensation scheme comprises a row-based scheme, wherein the at least one pixel of the array comprises pixels of a row of the array, and wherein acquiring the first reading is performed while corresponding pixel switches are open.
3. The method of claim 2 , wherein acquiring the second reading is performed while corresponding pixel switches are closed.
4. The method of claim 1 , wherein a temperature compensation scheme comprises a blind pixel scheme, wherein the at least one pixel of the array comprises entire pixels of the array, wherein pixels of one or more columns of the array comprise blind pixels that are shielded from optical exposure.
5. The method of claim 4 , wherein acquiring the first reading comprises performing a first row-based double sampling for blind pixels, and wherein acquiring the second reading comprises performing a second row-based double sampling for exposed pixels.
6. The method of claim 1 , wherein a temperature compensation scheme comprises a frame-based scheme, wherein the at least one pixel of the array comprises entire pixels of the array, wherein acquiring the first reading comprises performing a first frame-based double sampling while the array is not illuminated, and wherein acquiring the second reading comprises performing a second frame-based double sampling while the array is illuminated.
7. The method of claim 1 , wherein the temperature compensation method comprises a combination of at least two methods, wherein the at least two methods comprise a row-based method, a blind method and a frame-based method.