CMOS image sensor with compact pixel layout
An image sensor array of shared pixel units fabricated by a CMOS technology, wherein each pixel unit includes a plurality of photodiodes and respective transfer transistors and floating drains whose layout constitutes mirror images. The plurality of photodiodes each share a single reset transistor and source follower amplifier transistor wherein the shared floating diode is spaced at the minimum distance, from a gate electrode of the source follower transistor as is allowed by the CMOS fabrication technology chosen to manufacture the image sensor array.
1. An image sensor array of shared pixel units fabricated by a CMOS technology providing improved compactness and performance, each pixel unit comprising:
a first and second photodiode, each having associated adjacent first and second transfer transistors;
a first portion of a floating diode coupled to and adjacent to the first transfer transistor and a second portion of a floating diode coupled to and adjacent to the second transfer transistor;
a first portion of a reset transistor and a second portion of a reset transistor;
a first portion of a source follower amplifier transistor and a second portion of a source follower transistor; wherein the layout of the first photodiode, the first transfer transistor, the first portion of the floating diode, the first portion of the reset transistor and the first portion of the source follower transistor is a mirror image of the layout of the second photodiode, the second transfer transistor, the second portion of the floating diode, the second portion of the reset transistor and the second portion of the source follower transistor; and wherein the first and second portions of the reset transistor form a single reset transistor and the first and second portions of the source follower transistor form a single source follower transistor; and wherein the first and second portions of the floating diode form a single shared floating diode which is spaced at the minimum distance from a gate electrode of the source follower transistor as is allowed by the CMOS fabrication technology chosen to manufacture the image sensor array.
2. The pixel unit of the image sensor array of shared pixel units of claim 1 , wherein the spacing between the shared floating diode and the gate electrode of the source follower transistor is chosen from the range 0.05 micrometers to 0.25 micrometers.
3. The pixel unit of the image sensor array of shared pixel units of claim 1 , wherein the single reset transistor, the single shared floating drain, and the single source follower transistor are arranged along a horizontal line which constitutes the mirror image axis; and wherein the floating drain is coupled through a doped Silicon pathway on one side to the reset transistor and is spaced at the minimum distance from the gate electrode of the source follower transistor on its opposing side.
4. The pixel unit of the image sensor array of shared pixel units of claim 3 , additionally including a row select transistor electrically coupled to the source follower transistor and occupying a layout location at one of the two pixel unit corner locations lying along a vertical line running perpendicular to the horizontal mirror axis and through the source follower transistor.
5. The image sensor array of shared pixel units of claim 1 , comprising n rows and m columns of photodiodes wherein each pixel unit spans two rows and one column resulting in the use of n/2 rows and m columns of pixel units to layout the array of shared pixel units.