© 2013 Atmel 1 SAM D21 Peripheral Touch Controller Noise Immunity

2 © 2013 Atmel 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) Detect Integration (DI) Acquisition Features Filter_Level Auto Oversampling (Auto_OS) Frequency Hopping Video : 10VCI Bench Conclusion Presentation Outline

3 © 2013 Atmel Impact of noise on a Touch application

4 © 2013 Atmel Radiated Noise Definition Radiated noise correspond to unwanted ’noisy’ RF voltages emitted by external element from the system. Fluorescent lamp Induction plate

5 © 2013 Atmel Radiated noise Impact on touch application Lamp impact

6 © 2013 Atmel Conducted noise definition Impact on touch application EARTH Without noise With radiated noise No touch Touch Noise always present in the system

7 © 2013 Atmel Conducted noise Definition Conducted noise correspond to unwanted ’noisy’ RF voltages and currents carried by its external wires and cables. Common mode noise

8 © 2013 Copyright Atmel Corporation Conducted noise Impact on touch application Noisy Power supply (3.3V) Not tuned board

9 © 2013 Copyright Atmel Corporation Conducted noise definition Impact on touch application EARTH Without noise With conducted noise No touch Touch power supply lines maintain a stable difference between VDD and GND user’s finger now provides a return path and effectively couples noise directly into the capacitive sensor

10 © 2013 Copyright Atmel Corporation 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. Noise immunity International Standard IEC/EN

11 © 2013 Copyright Atmel Corporation PTC noise immunity features

12 © 2013 Copyright Atmel Corporation Manage by combination of hardware acquisition features and software post acquisition treatment. Fast and easy Tuning is possible using dedicated Library parameters PTC noise immunity features PTC acquisition/ software features 100K 16 IRQ Acquisition Module Sensitivity ctrl ADC Oversampling RSRS Compensation Circuit X Line Driver Input control Y0Y0 Y1Y1 Y 15 Result X0X0 X1X1 X 15 QTouch Library Set RSEL_VAL Set DI Set Filter_Level Set Auto_OS Set Frequency_Mode APIAPI

13 © 2013 Copyright Atmel Corporation PTC noise immunity features Post-processing and pre-processing features

14 © 2013 Copyright Atmel Corporation 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. PTC noise immunity features Serial Resistor (RSEL_VAL_x) 1-100k Acquisition Module Sensitivity ctrl ADC Oversampling RSRS Compensation Circuit X Line Driver Input control Y0Y0 Y1Y1 Y 15 X0X0 X1X1 X 15

15 © 2013 Copyright Atmel Corporation 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 PTC noise immunity features Detect Integration (DI) No touch reported No touch reported Touch reported No Touch reported

16 © 2013 Atmel Illustration : 10CI Bench Video

17 © 2013 Atmel Illustration : 10CI Bench Video Bench description Application to test Test Software Coupling / decoupling network Power amplifier 10cm standoff from earth plane CI Signal Generator

18 © 2013 Atmel Illustration : 10CI Bench Video Test 1 : Test Application without noise Configuration : Filter_Level = 4 Result: Good and fast operation

19 © 2013 Atmel Configuration : frequency = 150kHz, Filter_Level = 4 Result: Shows false detects and failures. Illustration : 10CI Bench Video Test 2 : First frequency of standard CI sweep (150kHz)

20 © 2013 Atmel Configuration : Frequency = 150kHz, Rs = 100k, Filter_Level = 32 Result: Works very well Illustration : 10CI Bench Video Test 3 : First frequency of standard CI sweep (150kHz)

21 © 2013 Copyright Atmel Corporation Illustration : 10CI Bench Video Test 5 : Test frequency = 265kHz Configuration : frequency = 256kHz, Rs = 100k, Filter_Level = 32 Result: Shows false detects, failures

22 © 2013 Copyright Atmel Corporation 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 © 2013 Copyright Atmel Corporation Illustration : 10CI Bench Video Test 6 : Test frequency = 267kHz (Harmonic Close to Oversampling kHz) Configuration : Frequency = 267kHz, Rs = 100k, Filter_Level = 64, Auto_OS = 8 Result: Shows flickering on both keys and slider LEDs

24 © 2013 Copyright Atmel Corporation Illustration : 10CI Bench Video Test 7 : Test frequency = 267kHz (Harmonic Close to Oversampling kHz) Configuration : Frequency = 267kHz, Rs = 100k, Filter_Level = 64, Auto_OS = 8 Frequency hopping enabled Result: Works very well

25 © 2013 Copyright Atmel Corporation 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. 03/04/2013 Introducing Atmel SAM D20 Flash MCUs Conclusion