Fingerprint sensor and method of transmitting a sensor image to reduce data size and data rate
A fingerprint imager uses a non-rectangular image readout to reduce the bandwidth and data size of the read-out image. Narrow-width rows in the central portion of the image are used to align successive partial image frames of the fingerprint to reconstruct a full image of the fingerprint using full-width rows of the fingerprint frames.
1. A method of reading and transmitting data from a two-dimensional image array to reduce transmission bandwidth in a fingerprint sensor, the array comprising rows of pixels, the method comprising:
reading a plurality of full-width rows from the array;
reading a plurality of partial-width rows from the array, wherein the partial-width rows are vertically adjacent to the full-width rows;
transmitting the data from the full-width rows over an interface as a plurality of full-width image frames; and
transmitting the data from the partial-width rows over the interface as a plurality of partial-width image frames, wherein the partial-width image frames are interleaved with the full-width image frames when transmitted over the interface.
2. The method of claim 1 wherein the interface is an analog interface.
3. The method of claim 1 wherein the interface is a digital interface.
4. The method of claim 1 wherein the interface is a digital signal interface with one bit per pixel, the bit level indicating the presence of a fingerprint ridge.
5. The method of claim 1 wherein the array has pixels only in areas of the array that are transmitted.
6. The method of claim 1 , wherein the full-width image frames include no overlapping image data.
7. The method of claim 1 , wherein the array is substantially rectangular, wherein an unused portion of the array adjacent to the partial-width rows is used for non image-sensing circuitry.
8. A fingerprint sensor for reduced read-out data size comprising:
a two-dimensional image array comprising a plurality of full-width rows of pixels and a plurality of partial-width rows of pixels, wherein the partial-width rows are vertically adjacent to the full-width rows;
an interface; and
circuitry adapted to:
read the full-width rows from the array,
read the partial-width rows from the array,
transmit the data from the full-width rows over the interface as a plurality of full-width image frames, and
transmit the data from the partial-width rows over the interface as a plurality of partial-width image frames, wherein the partial-width image frames are interleaved with the full-width image frames when transmitted over the interface.
9. The fingerprint sensor of claim 8 wherein the array is substantially rectangular, wherein an unused portion of the array adjacent to the partial-width rows is used for non image-sensing circuitry.
10. The fingerprint sensor of claim 8 wherein the interface is an analog interface.
11. The fingerprint sensor of claim 8 wherein the interface is a digital interface.
12. The fingerprint sensor of claim 8 wherein the interface is a digital signal interface with one bit per pixel, the bit level indicating the presence of a fingerprint ridge.
13. The fingerprint sensor of claim 8 wherein the array has pixels only in areas of the array that are transmitted.
14. The fingerprint sensor of claim 8 , wherein the full-width image frames include no overlapping image data.