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.

4. Switched Capacitors (cont.)

5. Switched Capacitors (cont.)

6. Switched Capacitors (cont.)

7. Switched Capacitors (cont.)

8. Switched Capacitors (cont.)

9. Switched Capacitors Example

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

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

20. With Finger Present

21. Change in Capacitance

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