CMOS image sensors
Complementary metal–oxide–semiconductor
CMOS image sensors
Some drawbacks of CCDs
Advantages and drawbacks of the CMOS image sensors
present applications of CMOS image sensors
Overall architecture
Basic pixel structures
PN junction photodiode
Active pixel sensor, 3T-APS
Sensor peripherals

Active pixel sensor, 3T-APS
First, the reset transistor MRS is turned on

PD is reset to the value Vdd −Vth
Vth is the threshold voltage of transistor MRS

MRS is turned off and the PD is electrically floated

The accumulated charge changes the potential in the PD; the voltage of the PD,VPD ,decreases according to the input light intensity

After an accumulation time, the select transistor MSEL is turned on and the output signal in the pixel is read out in the vertical output line.
When the read-out process is finished MSEL is turned off and MRS is again turned on to repeat the above process.