Differential Readout
Charge measurement circuits remove fixed pattern noise by taking two voltage samples per pixel cycle. Correlated double sampling subtracts the reset voltage level from the integrated signal voltage level to isolate photon generated charge. This subtraction removes kTC noise introduced during the pixel reset phase.
Analog and digital implementations execute this differential measurement at the column line level.
Noise Attenuation
Sampling the reset voltage immediately before charge transfer captures thermal noise stored on the node capacitance. Subtracting this reference from the subsequent signal reading cancels low frequency reset variations. Thermal noise reduction allows sensors to reach lower detection limits under faint light conditions.
Signal path amplifiers multiply the remaining net differential voltage before conversion.
Drift Correction
Thermal changes cause DC offset shifts in pixel reset levels during extended sensor operation. Subtraction of reference samples eliminates thermal drift from output signals. Continuous frame sampling maintains stable baseline values despite fluctuating die operating temperatures.
High dynamic range sensors rely on this process to prevent dark current drift from saturating output registers.
Verification Standard
Characterization verifies noise attenuation performance by measuring dark frame temporal noise across gain settings. Transducer testing confirms reset noise cancellation by comparing single sample noise against differential sample noise. Automated test suites certify that residual column offset variations remain within designated LSB limits.
