AN2226 - PSoC®1 - Using Correlated Double Sampling to Reduce Offset, Drift, and Low Frequency Noise

AN2226 presents low noise signal processing in PSoC® 1 through the use of Correlated Double Sampling (CDS) to reduce errors due to offset, drift, and low frequency noise. An analog front end for a type K thermocouple is used as a design example. For equivalent implementation in PSoC 3 or PSoC 5, see AN66444. For complete thermocouple system design see in PSoC 3 or PSoC 5, see AN75511. A project for analog front end for type K thermocouple is provided in the associated download.

Introduction

The thermocouple (TC) is a voltage output device that measures the temperature difference between the sensor tip and a reference junction (called the cold junction). This is a relative measurement and to be accurate, the reference lead temperature must also be known. Type K thermocouples have an average output of approximately 40.7 μV/°C. This output is approximately linear. For complete linearization, see AN75511.

Correlated Double Sampling (CDS) provides a means to efficiently subtract offset and remove drift, and low frequency noise from this sensitive measurement. This technique works just as well for differential measurements such as pressure sensors and load cells.

Reading the following application notes will aid in better understanding of this application note:

AN74170 – PSoC 1 Analog structure and configuration with PSoC Designer - Discusses in detail about the architecture of analog blocks in PSoC 1 and how they can be configured to implement a particular functionality.

AN2224 – Lower noise continuous time signal processing - Provide an introduction to semiconductor noise phenomena and specifics on PSoC noise parameters.

AN2219 – Selecting Analog Ground and reference - Describes the internal ground and reference settings in detail and how they can be routed at the output to provide a reference.
 

PSoC 1 - Correlated Double Sampling Video

This video presents low noise signal processing in PSoC® 1 through the use of Correlated Double Sampling (CDS) to reduce errors due to offset, drift, and low frequency noise.