Dual conversion gain high dynamic range image sensor readout circuit memory storage structure

An image sensing system, comprising:

• a pixel array including a plurality of dual conversion gain (DCG) pixels arranged into a plurality of rows and a plurality of columns;
• control circuitry coupled to the pixel array to control operation of the pixel array;
• a plurality of readout circuits coupled to the pixel array to read out pixel data from the pixel array, wherein the pixel data includes low conversion gain (LCG) pixel data and high conversion gain (HCG) data, wherein each readout circuit includes:
• a ramp generator coupled to output a ramp signal;
• a comparator, wherein a first input of the comparator is coupled to receive the ramp signal from the ramp generator, wherein a second input of the comparator is coupled to a respective one of a plurality of column bitline outputs of the pixel array to receive an output signal from one of the plurality of DCG pixels, wherein the output signal is one of an LCG signal or an HCG signal;
• a counter coupled to receive an output of the comparator;
• a first memory circuit and a second memory circuit coupled to receive an output of the counter, wherein the counter is coupled to write to only one of the first and second memory circuits at a time in response to a memory write select signal;
• a first multiplexor, wherein a first input of the first multiplexor is coupled to receive an initial value, wherein a second input of the first multiplexor is coupled to receive an initial memory value from the first memory circuit, wherein the counter is coupled to load either the initial value or the initial memory value from an output of the first multiplexor in response to an initial select signal;
• a second multiplexor, wherein a first input of the second multiplexor is coupled to the first memory circuit, wherein a second input of the second multiplexor is coupled to the second memory circuit, wherein the second multiplexor is coupled to load either an LCG memory value from the first memory circuit or an HCG memory value from the second memory circuit from an output of the second multiplexor in response to a memory read select signal;
• and
• a data transmitter circuit coupled to the output of the second multiplexor to transmit pixel data of the pixel array;
• and
• a digital processor coupled to the readout circuits to receive the pixel data from the pixel array.

The image sensing system of 10, wherein each DCG pixel comprises:

• a photodiode coupled to photogenerate image charge in response to incident light;
• a first floating diffusion coupled to store the image charge photogenerated in the photodiode;
• a transfer transistor coupled to transfer the image charge from the photodiode to the first floating diffusion in response to a transfer signal;
• an amplifier transistor coupled to the first floating diffusion to amplify the image charge stored in the first floating diffusion to generate the output signal;
• a row select transistor coupled to the amplifier transistor to output the output signal in response to a row select signal;
• a DCG transistor coupled to the first floating diffusion to couple a DCG capacitor to the first floating diffusion in response to a DCG signal;
• and
• a reset transistor coupled to a voltage to reset the first floating diffusion in response to a reset signal.