HMI
High performance wearables can be energy efficient
Luciano Duca, general manager, solution marketing, Toshiba Electronics Europe, talks about recent processor development ease design challenges
A
ll too often, wearable devices are bought on an impulse and end up left in the drawer within six months.
In this exciting new area the term 'stickiness' encompasses the whole user experience, covering everything from how valuable the apps are through to the longevity of the battery between charges. As devices become more sophisticated and power-hungry, delivering 'sticky' solutions becomes more challenging. Finding the best trade-off between functionality, performance and battery life is an important challenge for the wearable tech designer. This means careful consideration of embedded processor technologies.
Evolution of wearable technology Wearables now dominate the Internet-of- Things (IoT) with, according to Gartner, over four billion devices already connected, increasing by 5.5 million devices every day. Many wearables currently connect to the outside world via a smartphone, yet the latest wearables are closer to the smartphone itself than earlier unconnected devices. Indeed, much of the recent innovation – from MMI interfaces for displays / touchscreens and wireless connectivity elements including BLE, WiFi and GPS - finds its roots in smartphone technology. The need for wearable devices with high levels of functionality, outstanding performance and excellent battery life is undeniable. Creating devices that are sufficiently compelling that the user will keep using them and upgrade to the next generation is a major challenge for designers. Research shows a third of all activity trackers purchased were discarded
in the first six months of ownership and half are no longer used. Lack of functionality, operating difficulties, and inconvenience, are major contributors to this trend.
Design challenges To create a compelling wearable solution, several functional blocks have to be squeezed into a very small space. The challenge includes all design aspects
- processors, batteries, power management, displays, audio, MMI, interfaces and security sections. In addition, a whole range of sensor inputs have to be integrated. Often the requirements compete; for example, a larger, faster processor increases functionality and performance, but size and battery life suffer. Always-on sensors and communications drain batteries, so designers have to devise schemes to power these off until they are needed. To manage the complexities of providing high performance in a small package with extended battery life, designers must select the processor carefully.
Integrated processor technology for wearable devices Specific processors for IoT and wearable devices are now available from several companies. For example, Toshiba’s ApP Lite family of application processors, including the latest TZ1200, is specifically targeted at wearables including activity monitors and smart watches. The TZ1200 processor is based on a high-performance 32-bit ARM Cortex-M4F RISC floating-point core with memory protection and a flexible interrupt processor operating up to 120MHz. The on-board power management functionality gives the TZ1200 an active current consumption of just 78 A/MHz in normal operation. Meaning that, with a 200mAh battery, endurance is about a week in pulse management applications and a month in watch applications.
Figure 1: Smart, connected wearable device - example block diagram 34 November 2016 Components in Electronics
In addition to 2.2MB of embedded high- speed SRAM, the TZ1200 incorporates external memory interfaces including SPI NOR, SPI NAND and e•MMC. An advanced
LCD controller / 2D graphics engine supports MIPI Display Bus Interface (DBI) and Display Serial Interface (DSI) protocols compatible with HVGA (480x320) displays at 30fps and QVGA displays refreshed at 50fps. The 2D Graphics Accelerator (GFX) provides a powerful platform for drawing, rotating and resizing images as well as performing colour conversion. These autonomous blocks reduce processor load, contributing to further power efficiencies. As a result, designers can
create high-end graphics with a low CPU load and
Figure 2: The advanced, low-power, graphics engine is ideal for sophisticated wearables
ultra-low power consumption. In 'always- on' applications such as a watch with a moving second hand, the current consumption is as low as 450uA. For applications that only update periodically (e.g. a watch with no second hand) the current draw reduces by a factor of 15 to a miserly 30uA.
Thus, with the powerful graphics engine and the ability to produce graphical data with ease at low power consumption, the TZ1200 is ideally suited to being used as the core component in smart watches and other similar wearable devices such as healthcare and fitness devices. In fact, many wearable devices based upon the TZ1200 only need to be charged once every month. A lossless compress and decompress
hardware engine supported by integrated USB, UART, SPI and I2C interfaces eases the integration of sensors and peripherals to monitor activity and/or movement. The high-precision analogue front-end (AFE) brings together a 24-bit delta- sigma ADC, 12-bit ADC, 12-bit DAC and an LED DAC and is a particularly important aspect of the new processor. Most notably, the AFE supports direct sensing, directly connecting analogue sensors to the high-resolution ADC offering significant space and power savings and reducing EMI. Eliminating the ‘pre-conditioning’ high pass filter, high gain amplifier and low pass filter simplifies design as these conditioning functions are performed by software running directly on the processor. Thus, the AFE simplifies implementation and improves the performance of key wearable functionality such as impedance measurement (for galvanic skin response or GSR), voltage measurement (used for ‘right leg drive’ ECG monitoring) and the current measurement required for LED-based PPG (photoplethysmographic) pulse rate sensing and SpO2 (pulse oximeter oxygen saturation) measurement.
Example application – pulse rate solution
Pulse rate monitoring is a fundamental application for fitness-oriented wearables. To the user such monitoring must appear to be continuous yet, in reality, continuous monitoring significantly impacts power consumption and battery life. Conventional designs that use external filtering are inflexible in terms of continuous monitoring, as shown below. Depending on the resolution
required (optimisation of accuracy and speed are set for each application) the TZ1200 is configurable to differing intermittent operation rates. This can reduce the total current draw of the application by over 98 per cent when compared to a conventional design. Furthermore, because the 24-bit ADC has a x16 FIFO, the CPU does not need to wake every time a sensor signal is received meaning that the average, overall current consumption can reduce to 0.85mA.
Support In order to bring compelling products to market quickly, designers require sophisticated support from manufacturers to facilitate rapid prototyping and debugging. Toshiba's evaluation board for the TZ1200 ApP Lite processor includes SPI-Flash and e•MMC memory, audio I/O, a 6-axis sensor, a DSI display with touch panel and onboard Bluetooth low energy communications. The evaluation package includes
software to support rapid GUI creation, and a library of images and graphics middleware for image handling. The evaluation board can also be used in conjunction with support tools and BSPs from leading embedded systems tool vendors.
www.toshiba.semicon-
storage.com/eu/top.html
www.cieonline.co.uk
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52