SAM D21 Peripheral Touch Controller

1. SAM D21 Peripheral Touch Controller Noise Immunity

2. PresentationOutline • Impact of noise on a touch application • Noise sources • Noise immunity standard • Peripheral Touch Controller noise immunity features • Pre-processing and post-processing features • Serial Resistor (Rs) • DetectIntegration (DI) • Acquisition Features • Filter_Level • Auto Oversampling (Auto_OS) • FrequencyHopping • Video : 10VCI Bench • Conclusion

3. Impact of noise on a Touch application

4. Radiated Noise Definition Radiated noise correspond to unwanted ’noisy’ RF voltages emitted by external element from the system. Fluorescent lamp Induction plate

5. Radiated noise Impact on touch application Lamp impact

6. Conducted noise definition Impact on touch application Touch No touch Without noise Withradiated noise earth Noise always present in the system

7. Conducted noise Definition Conducted noise correspond to unwanted ’noisy’ RF voltages and currents carried by its external wires and cables. Common mode noise

8. Conducted noise Impact on touch application Noisy Power supply (3.3V) Not tuned board

9. Conducted noise definition Impact on touch application Touch No touch Without noise earth Withconducted noise user’s finger now provides a return path and effectively couples noise directly into the capacitive sensor power supply lines maintain a stable difference between VDD and GND

10. Noise immunity International Standard IEC/EN 61000-4-6 • Define Common reference and a set of testing methods • Modulated RF signal stepped over the frequency range from 150kHz to 80MHz. • At each step there is a ’dwell period’ whilst the EUT (Equipment Under Test) is checked for performance degradation. • Result classifications : • Class A – No significant degradation. • Class B – Degradation in operation but the product fully recovers once the stress is removed without any operator intervention. (no loss of data) • Class C – Operation is affected and operator intervention is required (no loss of data) • Class D – Unrecoverable loss of function or degradation of performance. Loss of data may occur.

11. PTC noise immunity features

12. PTC noise immunity features PTC acquisition/ software features • Manage by combination of hardware acquisition features and software post acquisition treatment . • Fast and easy Tuning is possible using dedicated Library parameters • QTouch Library • Set RSEL_VAL • Set DI • Set Filter_Level • Set Auto_OS • Set Frequency_Mode API Compensation Circuit Input control Y0 IRQ RS • AcquisitionModule • Sensitivity ctrl • ADC • Oversampling Y1 Result Y15 100K 16 X0 X1 X Line Driver X15

13. PTC noise immunity features Post-processing and pre-processing features

14. PTC noise immunity features Serial Resistor (RSEL_VAL_x) • Increasing the impedance of the signal path can significantly improve immunity to conducted noise while maintaining the overall signal integrity. • Intermediate resistor value can be chosen to achieve the required level of noise suppression while meeting other system design requirements such as power consumption and response time. Compensation Circuit Input control Y0 RS • AcquisitionModule • Sensitivity ctrl • ADC • Oversampling Y1 Y15 1-100k X0 X1 X Line Driver X15

15. PTC noise immunity features Detect Integration (DI) • Principle : Post processing Filter that requires several consecutive measurements to confirm touch/Release (Similar to debounce system) • Example DI = 3 : • DI Limit range • A DI count of 3 is the minimum practical setting • A DI count of 6 is common • Higher values : better noise immunity, slower response No touch reported No touch reported Touch reported No Touch reported

16. Illustration : 10CI Bench Video

17. Illustration : 10CI Bench Video Bench description Test Software CI Signal Generator Power amplifier Coupling / decoupling network 10cm standofffromearth plane Application to test

18. Illustration : 10CI Bench Video Test 1 : Test Application without noise • Configuration : Filter_Level = 4 • Result: Good and fast operation

19. Illustration : 10CI Bench Video Test 2 : First frequency of standard CI sweep (150kHz) • Configuration : frequency = 150kHz , Filter_Level = 4 • Result: Shows false detects and failures.

20. Illustration : 10CI Bench Video Test 3 : First frequency of standard CI sweep (150kHz) • Configuration : Frequency = 150kHz, Rs = 100k, Filter_Level = 32 • Result: Works very well

21. Illustration : 10CI Bench Video Test 5 : Test frequency = 265kHz • Configuration : frequency = 256kHz, Rs = 100k, Filter_Level = 32 • Result: Shows false detects, failures

22. Illustration : 10CI Bench Video Test 5 : Test frequency = 265kHz • Configuration : Frequency = 256kHz , Rs = 100k , Filter_Level = 64, Auto_OS = 8 • Result: Works very well

23. Illustration : 10CI Bench Video Test 6 : Test frequency = 267kHz (Harmonic Close to Oversampling 266.67kHz) • Configuration : Frequency = 267kHz , Rs = 100k , Filter_Level = 64, Auto_OS = 8 • Result: Shows flickering on both keys and slider LEDs

24. Illustration : 10CI Bench Video Test 7 : Test frequency = 267kHz (Harmonic Close to Oversampling 266.67kHz) • Configuration : Frequency = 267kHz , Rs = 100k , Filter_Level = 64, Auto_OS = 8 Frequency hopping enabled • Result: Works very well

25. Conclusion • When dealing with noise immunity, It is important to understand the environment in which the touch application is designed to operate in, and where appropriately apply suitable techniques to address the effects of unwanted noise disturbances. • The Peripheral touch controller embed in SAM D21 and associated Software Library provide key features for building suitable touch application with techniques to overcome noise disturbance . Introducing Atmel SAM D20 Flash MCUs