Image sensor and method of operating the same

Abstract

A method of operating an image sensor includes generating a plurality of sub pixel signals using a sub pixel group. The sub pixel group includes a plurality of sub pixels and corresponds to a single pixel. The method further includes generating a pixel signal having a plurality of bits based on a result of comparing the sub pixel signals with a reference voltage. Each of the sub pixels is a 1-transistor (1T) pixel that detects at least one photogenerated charge and includes only one transistor.

What is claimed is: 
     
         1 . A method of operating an image sensor, the method comprising:
 generating a plurality of sub pixel signals using a sub pixel group, the sub pixel group including a plurality of sub pixels and corresponding to a single pixel; and   generating a pixel signal having a plurality of bits based on a result of comparing the sub pixel signals with a reference voltage,   wherein each of the sub pixels is a 1-transistor (1T) pixel that detects at least one photogenerated charge and includes only one transistor.   
     
     
         2 . The method of  claim 1 , wherein the sub pixels are arranged in a matrix of “n” rows and “m” columns in the sub pixel group, and
 the generating the pixel signal comprises: 
 comparing the sub pixel signals with the reference voltage to generate comparison signals for the respective columns; 
 generating a count result by counting each of the comparison signals; and 
 adding count results generated for the respective columns to generate the pixel signal. 
 
     
     
         3 . The method of  claim 2 , wherein the generating the pixel signal further comprises:
 transmitting sub pixel signals output to each of the columns to an input node of a comparator using a capacitor; and   resetting the input node of the comparator to a power supply voltage.   
     
     
         4 . The method of  claim 3 , wherein the generating the pixel signal further comprises:
 sequentially increasing a voltage of the input node of the comparator by a hole voltage.   
     
     
         5 . The method of  claim 4 , wherein the generating the pixel signal further comprises:
 resetting an output node of the comparator to a ground voltage.   
     
     
         6 . The method of  claim 1 , wherein a threshold voltage of the single transistor is changed according to the at least one photogenerated charge. 
     
     
         7 . An image sensor comprising:
 a pixel array comprising a plurality of sub pixel groups, each of the sub pixel groups including a plurality of sub pixels and corresponding to a single pixel;   a readout block configured to generate a pixel signal having a plurality of bits based on a result of comparing a plurality of sub pixel signals generated by each of the sub pixel groups with a reference voltage; and   a control unit configured to control the pixel array and the readout block,   wherein each of the sub pixels is a 1-transistor (1T) pixel that detects at least one photogenerated charge and includes only one transistor.   
     
     
         8 . The image sensor of  claim 7 , wherein the sub pixels are arranged in a matrix of “n” rows and “m” columns in each of the sub pixel groups, and
 the readout block comprises: 
 a comparator configured to compare sub pixel signals of each of the columns with the reference voltage to generate a comparison signal for each column; 
 a counter configured to generate a count result by counting the comparison signal; and 
 an adder configured to generate the pixel signal by adding count results generated for the respective columns. 
 
     
     
         9 . The image sensor of  claim 8 , wherein the counter is an asynchronous counter that receives the comparison signal as a clock signal. 
     
     
         10 . The image sensor of  claim 9 , wherein the readout block further comprises:
 a capacitor configured to transmit the sub pixel signals to an input node of the comparator; and   a first reset switch configured to reset the input node of the comparator to a power supply voltage.   
     
     
         11 . The image sensor of  claim 10 , wherein the readout block further comprises:
 a hole injection unit configured to sequentially increase a voltage of the input node of the comparator by a hole voltage.   
     
     
         12 . The image sensor of  claim 11 , wherein the hole injection unit comprises a plurality of hole injection transistors which are connected in series between the power supply voltage and the input node of the comparator. 
     
     
         13 . The image sensor of  claim 12 , wherein the hole injection transistors are P-channel metal oxide semiconductor (PMOS) transistors. 
     
     
         14 . The image sensor of  claim 11 , wherein the readout block further comprises a second switch configured to reset an output node of the comparator to a ground voltage. 
     
     
         15 . The image sensor of  claim 7 , wherein a threshold voltage of the single transistor is changed according to the at least one photogenerated charge. 
     
     
         16 . A method of operating an image sensor, comprising:
 receiving, at a readout circuit, a plurality of sub pixel signals from a plurality of one transistor pixels;   generating, by the readout circuit, a pixel signal based on the received sub pixel signals and a reference voltage.   
     
     
         17 . The method of  claim 16 , wherein the generating comprises:
 comparing each of the sub pixel signals to the reference voltage; and   generating the pixel signal based on results of the comparing.   
     
     
         18 . The method of  claim 16 , wherein the generating comprises:
 producing count values, each count value associated with a respective once of the sub pixel signals based on a duration that a voltage corresponding to the respective sub pixel signal meets a relationship with the reference voltage; and   determining the pixel signal based on the generated count values.   
     
     
         19 . The method of  claim 18 , wherein the generating comprising:
 changing the voltage corresponding to the respective sub pixel signal over time.