Ultra-high dynamic range CMOS sensor
An imaging array having a plurality of pixel sensors connected to a bit line is disclosed. Each pixel sensor includes a capacitive overflow pixel sensor characterized by an overflow capacitor having a switching terminal, and a floating diffusion node, a buffer amplifier that connects the floating diffusion node to a bit line in response to row select signal, and a switch that connects the switching terminal to either ground or a boost voltage. The imaging array also includes a switch controller that controls the switch and is connected to the bit line, the switch controller determining a voltage on the bit line, the switch controller connecting the switching terminal to the boost voltage during an exposure of the pixel sensor to light and to either ground or the boost voltage during a readout of charge stored on the overflow capacitor depending on the voltage on the bit line.
1. An apparatus comprising a plurality of pixel sensors connected to a bit line, at least one of said pixel sensors comprising:
a capacitive overflow pixel sensor characterized by an overflow capacitor having a switching terminal, and a floating diffusion node;
a buffer amplifier that connects said floating diffusion node to said bit line in response to a row select signal;
a switch that connects said switching terminal to either ground or a boost voltage; and
a switch controller that controls said switch and is connected to said bit line, said switch controller determining a voltage on said bit line, said switch controller connecting said switching terminal to said boost voltage during an exposure of said pixel sensor to light and to either ground or said boost voltage during a readout of charge stored on said overflow capacitor depending on said voltage on said bit line.
2. The apparatus of claim 1 wherein said switch controller outputs a signal indicative of whether said switching terminal was connected to ground or said boost voltage during said readout.
3. The apparatus of claim 1 wherein said switch controller comprises a comparator that compares said voltage on said bit line with a predetermined reference voltage, said comparator having an output of either ground or said boost voltage if said voltage on said bit line is greater than, or less than or equal, to said predetermined reference voltage, respectively.
4. The apparatus of claim 3 wherein said floating diffusion node is characterized by a voltage swing on said floating diffusion node and wherein said predetermined reference voltage is chosen to maximize said voltage swing.
5. The apparatus of claim 1 wherein said capacitive overflow pixel sensor are constructed in a process that sets a maximum allowed voltage across a gate in said capacitive overflow pixel sensor and wherein said floating diffusion node are reset to a reset voltage prior to exposing said apparatus to light, said boost voltage plus said reset voltage being less than said maximum allowed voltage.