Correlated double sampling (CDS
) is a method to measure electrical values such as
voltage
Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge t ...
s or
currents that allows removing an undesired offset. It is used often when measuring sensor outputs. The output of the sensor is measured twice: once in a known condition and once in an unknown condition. The value measured from the known condition is then subtracted from the unknown condition to generate a value with a known relation to the physical quantity being measured.
This is commonly used in
switched-capacitor A switched capacitor (SC) is an electronic circuit that implements a function by moving charges into and out of capacitors when electronic switches are opened and closed. Usually, non-overlapping clock signals are used to control the switches, so ...
operational amplifiers to effectively double the gain of the charge sharing opamp, while adding an extra phase.
When used in imagers, correlated double sampling is a noise reduction technique in which the reference voltage of the pixel (i.e., the pixel’s voltage after it is reset) is subtracted from the signal voltage of the pixel (i.e., the pixel’s voltage at the end of integration) at the end of each integration period, to cancel
kTC noise (the thermal noise associated with the sensor's capacitance).
See also
*
Dark-frame subtraction
In digital photography, dark-frame subtraction is a way to reduce image noise in photographs shot with long exposure times, at high ISO sensor sensitivity or at high temperatures. It takes advantage of two components of image noise that remain t ...
References
Electricity
Measurement
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