Capacitive Touch Based User Interfaces and Hardware-based Solutions

Capacitive Touch Based User Interfaces and Hardware-based Solutions...  Adoption of technology is happeningExpansion of Capacitive Touch Key Interfaces... Why Use Capacitive Touch Inter

Capacitive Touch Based User Interfaces and Hardware-based Solutions

Renesas Technology & Solution Portfolio

Microcontroller and Microprocessor Line-up

44 DMIPS, True Low Power Embedded Security, ASSP

25 DMIPS, Low Power

 Industrial & Automotive, 150nm

 190µA/MHz, 0.3µA standby

 Industrial, 90nm

 242µA/MHz, 0.2µA standby

 Automotive & Industrial, 90nm

 600µA/MHz, 1.5µA standby

 Automotive & Industrial, 65nm

 500µA/MHz, 35µA deep standby

Market Trend

 Adoption of technology is happening

Expansion of Capacitive Touch Key Interfaces

 Audience:

 Why would you use a touch interface?

Why Use Capacitive Touch Interfaces

Typical System Configurations

 1 touch channel does not necessarily mean 1 key

Touch Channel vs Key vs PCB Electrode

Ch0 Ch1 Ch2 Ch3 Ch4 Ch5 Ch6 Ch7

Touch Controller

Key1 Key2 Key3

Key4 Key5 Key6

Key7 Key8 Key9

Matrix Configuration.

Direct Key Configuration

 Dedicated IC for touch sensing

 Single-chip reduces BOM cost

Configuration Example (Touch Sensor IC)

System Controller

Touch Sensor IC

1 4

Serial I/F

3

3 2

Single-chip

Examples of Focused Applications

communication

communication

Design Considerations

Typical Touch Key Design Flow

1 • Specify touch requirements (ex: type of touch I/F, # of keys, overlay), and other system constraints including mechanical

2 • Evaluate options with actual hardware (ex: Kit)  select best fit solution

3 • Design per vendor’s recommendations (including PCB layout, noise countermeasures)

4 • Initial testing and tuning of hardware + software (including noise filtering) If performance not met go back to step #3

 All solutions based on same concept: measurement of

change in capacitance

 Must maximize signal-to-noise ratio

 System-level design considerations, not just a sensor IC

Reliable Capacitive-based Touch Key Detection

Noise Noise Signal

Touch Design Considerations (Hardware)

Touch Design Considerations (Firmware)

• Scanning should not be interrupted

• Need multiple charging/discharging and measurements for good accuracy

Measurement

• Software tuning to maximize SNR

• Real-time monitoring while touch detection

• Source code (APP + Touch) for optimization

Tuning and Debugging

• Multi-touch, wheel/slider decoding, water detection/suppression: application-specific

Application-Level

Touch Functions

Renesas Touch Key Solution

Sensor Control Unit (SCU) Detection:

 Connect one sensor channel to CHxA using internal MUX

 Charge Cc by driving CHxC High

 Switch CHxC to Hi-Z mode

 Discharge Cc through Rc by driving CHxB Low

 Switch CHxB to Hi-Z mode

 Check the logic level of ChxA

 If logic level is still high repeat steps 4,5 and 6 until the logic level goes low

 Major components…

Simplified Hardware Circuit

Charge Circuit Circuit Control Capacitance Detection

Touch Electrode

 Repeat discharge and re-distribution

Circuit Operation

Test if Vct below Vref

No = Count channel up Yes = Cycle complete

 Tracking counts vs time

Touch…Analog to Digital

‘Counts’

 Control, Status, and Error Management

 Measurement and Sequencing/Scanning

 Noise Countermeasure

 Data transfer

Status decoder

Timing variable counter

Channel control counter

Status counter (5-bits)

Channel control block

Secondary counter

Measurement block

Count source control block

Trigger control block

Clock

Trigger

Signal

Touch Signal

Channel Selection

Sensor Control Unit (SCU)

1

3

1

4 2

1

1

1 1

Software-based

solution

 In software solution, CPU is utilized 100%

R8C T-SCU CPU Utilization

Single-chip MCU for Touch + System Control

1.8V–5.5V

COMM RAM Flash

.

Step-down

converter IC

CPU

Wheel Renesas Touch MCU (R8C/3xT)

R8C/3xT Low Power Consumption

Clock Source Low-speed

OCO High-speed OCO High-speed OCO Peripheral Clock 125kHz 5MHz 5MHz

Average Current = ~16 µA for 1 channel

Optimized Software Architecture

Sensor

Functional

Implementation

User Application

Reference and Threshold

Sensor Touch Decision

(Binary)

Drift Compensation

Wheel Decoder Decoder Switch

Matrix Decoder Calibration Auto

Functional Noise Rejection (Debounce, Wipedown) Application

 Complete Touch Sensor API as source code

Circuit Modeling

Measurement Intuitive GUI

Parameter Setting

Advanced Tuning Tools

Benefits of Renesas Capacitive Touch Solution

Hardware-Assisted Touch High Integration

• <15% of CPU utilization

• Built-in noise countermeasures

• Touch sensing in standby

• Full peripheral functions for system control

• Reduced system cost

R5F213J4T R5F213J5T R5F213J6T

R5F213N7T

R5F2136AS R5F2136CS

R5F21388S R5F2138AS R5F2138CS

Renesas Touch MCU (R8C/3xT) Line-up

SCU TSCU

 Evaluation System Features

Self-contained Touch Evaluation System

Online Resources for Touch MCU Solutions

Questions?