This document introduces the CSA and CSD capacitive sensing methods. CSA uses successive approximation to find the capacitance value by charging and discharging the sensor capacitor until the voltage matches a reference level. CSD uses a sigma-delta modulator to compare the sensor capacitor to a reference and outputs a bit stream. Both methods detect changes in capacitance by measuring how long it takes to charge the sensor capacitor, with increased capacitance resulting in a faster charge time and higher output value. The value is then processed to determine if a touch is present.

1. Introduction to Capacitive Sensing Source: Cypress Part2: CSA And CSD CapSense

2. Module Introduction Purpose This module introduce the CSA and CSD Capacitive Sensing. Outline Introduction to CSA Capacitive Sensing. Introduction to CSD Capacitive Sensing. Contents 32 pages Duration 15 Minutes

3. Sidebar: Switched Capacitors Method for developing analog components with basic CMOS technologies

4. Switched Capacitors (cont.)

5. Switched Capacitors (cont.)

6. Switched Capacitors (cont.)

7. Switched Capacitors (cont.)

8. Switched Capacitors (cont.)

9. Switched Capacitors Example

10. Making Sense of It Detect the difference between the presence or absence of conductive element: Continuously read the sensor capacitance Digitize the readings Cancel out the noise Compare to a threshold Make a decision based on the value

11. CapSense Sensing Methods CapSense Successive Approximation (CSA) CapSense Sigma-Delta (CSD)

12. CSA Sensing Method

13. CSA Sensing Method

14. CSA Sensing Method

15. CSA Waveform

16. Equivalent Resistance Replace the sensor capacitor (C X ) with its equivalent resistance

17. Region 1 Find an iDAC current value where voltage across R CX (V Start ) is just below V REF Successive approximation used to find golden iDAC current Done once for each sensor in the CSA_Start() API

18. Count long it takes for the voltage return to V REF Region 2

19. Update the baseline Compare measurement to the baseline Determine button status / centroid location Region 3 Process measured values in firmware

20. With Finger Present

21. Change in Capacitance

22. CSA Summary Increase in C x reduces R Cx , lowering the starting voltage, V start Lower starting voltage causes longer charge time Large charge time enables the counter for a longer time Due to the counter’s longer enable time, higher raw counts are measured Comparator triggers when V start is equal to V REF , stopping counter The raw counts are processed by firmware Update the baseline Compare measurement to the base line Determine button status / centroid location

23. CSD Sensing Method

24. CSD Sensing Method

25. CSD Sensing Method

26. CSD Sensing Method

27. Equivalent Resistance

28. Sigma-Delta Modulator

29. Sigma-Delta Modulator

30. Bit Stream Filter

31. CSD Method

32. CSD Summary Increase in C x reduces R Cx , allowing more current to charge C Mod More current causes C Mod to charge faster Faster charge time increases the duty cycle Larger duty cycle enables the counter for a longer time Due to the counter’s longer enable time, higher raw counts are measured The raw counts are processed by firmware Update the baseline Compare measurement to the baseline Determine button status / centroid location

33. Additional Resource For ordering PSoC, please click part list or call our sales hotline For additional inquires contact our technical service hotline For more product information go to http://www.cypress.com/capsense/ Newark Farnell