CY8CKIT-025 PSoC® Precision Analog Temperature Sensor Expansion Board Kit Guide, Doc. # 001-65791 Rev. *J
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Example Projects
5.3.3.3.4
Correlated Double Sampling (CDS)
Correlated double sampling is a technique where the offset and low frequency noise is eliminated by
subtracting a zero voltage reading from every voltage sample. See application notes
and
for more details on correlated double sampling. The ADCMux, Channel 8, is used to make
zero-voltage measurement for the DS600. To make zero-voltage measurement for the RTD and
diode, pass a zero current through the RTD, diode, or calibration resistor and measure the ADC out-
put across the RTD/diode/calibration resistor.
5.3.3.3.5
Calibration
For this project, user calibration is not available for the temperature sensors. The 3.3 V and 5 V mea-
surements are adjusted by a calibration factor. This is because the ADC configuration (±6.144 V
ADC input range) used to read the 3.3 V and 5 V rail is not factory calibrated. To achieve this calibra-
tion factor, a voltage is read with one of the factory calibrated ADC ranges (ADC configuration 1 –
±1.024 V range); that same value is read with the non-factory calibrated range. The ratio of these
two readings is then used to adjust the 3.3 V and 5 V measurements. This calibration is done before
the main code loop.
