Correlated double sampling

Correlated Double Sampling(CDS) is a technique for measuring electrical values such as voltages or currents that allows for removal of an undesired offset. It is used quite frequently 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 operational amplifiers to effectively double the gain of the charge sharing opamp (while adding an extra phase).