High efficiency CMOS image sensor pixel employing dynamic voltage supply
View Patent ↗A global shutter compatible pixel circuit comprising a reset gate (RG) transistor is provided in which a dynamic voltage is applied to the drain of the reset gate transistor in order to reduce a floating diffusion (FD) leakage therethrough during signal hold time. The drain voltage of the reset gate transistor is held at a lower voltage than a circuit supply voltage to minimize the off-state leakage through the RG transistor, thus reducing the change in the voltage at the floating diffusion during the signal hold time. In addition, a design structure for such a circuit providing a dynamic voltage to the drain of a reset gate of a pixel circuit is also provided.
1. A method of operating a semiconductor circuit of an array of image sensor pixels, said method comprising:
exposing an entirety of said array simultaneously, while applying a first voltage to each drain of reset gate transistors in said entirety of said array;
applying a second voltage to each drain of said reset gate transistors of said entirety of said array after said exposing of said entirety of said array, wherein said second voltage is less than said first voltage and is from 10% to 90% of said first voltage; and
transferring data from said array of image sensor pixels row by row, wherein a hold time between said exposing of said entirety of said array and said transferring is different from row to row.
2. The method of claim 1 , wherein a switching between said first voltage and said second voltage is accommodated by a switchable voltage supply circuit connected to a system power supply voltage and an alternate voltage lower than said system power supply voltage.
3. The method of claim 1 , wherein said first voltage and said second voltage is provided by a control signal configured to be set at two different voltages and directly applied to at least one transistor of said image sensor pixel.
4. The method of claim 3 , wherein said at least one transistor includes a reset gate transistor within said image sensor pixel, and wherein said control signal is directly connected to a gate of said reset gate transistor.
5. The method of claim 3 , wherein said image sensor pixel comprises:
a source follower transistor including a source follower transistor source and a source follower transistor gate, wherein said source follower transistor gate is directly connected to a floating diffusion node; and
a row select transistor including a row select transistor drain and a row select transistor source, wherein said row select transistor drain is directly connected to said source follower transistor source and said row select transistor source is configured to provide an output signal of said image sensor pixel.
6. The method of claim 5 , wherein said at least one transistor includes said row select transistor, and wherein said control signal is directly connected to a gate of said row select transistor.