JUNE 2015
Ambient Light Sensors in Wearable Devices ROHM Sensor Platform Overview
Interview with Thomas Stockmeier COO of ams
Sensing the FUTURE
ams’ Plans to Shape the World with Sensor Solutions
Join Today Today CLICK HERE Join
eeweb.com/register
CONTENTS
SENSOR TECHNOLOGY
EEWeb FEATURE Inside the Apple Watch A Look at the Sensors Behind the Most Popular Smartwatch
PRODUCT WATCH ROHM Sensor Platform Kit Crouzet Level Control Relays
INDUSTRY INTERVIEW Sensing the Future Interview with Thomas Stockmeier – COO of ams
TECH REPORT Ultra-small Ambient Light Sensors The Need for ALS in New Wearable Devices
CONTENTS
4 10 16 20 26
3
SENSOR TECHNOLOGY
The Sensor Technology
Behind the
Apple Watch
Photo by Raysonho @ Open Grid Scheduler / Grid Engine (Own work) [CC0], via Wikimedia Commons
4
By Rob Riemen EEWeb Contributing Author
EEWEB FEATURE
W
ith the recent release of the Apple Watch,
wearable electronics are becoming more and more mainstream. The Apple Watch may just seem like another expensive replacement for a smartphone, but the device is marketed as Apple’s most “personal” device yet, with constant contact with the user’s wrist and a suite of sensors that deliver health data and vitals statistics. With the advent of microelectromechanical systems (MEMS) and the technological advancement of the sensors used in these systems, it is possible to make a watch do way more than just tell time.
5
SENSOR TECHNOLOGY
Photo by Henriok (Own work) [CC0], via Wikimedia Commons
Wearable electronics generally use sensors to track certain aspects of the user’s life. The Apple Watch includes an accelerometer, a gyroscope, and a barometer—all of which are pretty common in smaller wearables. Along with these sensors, the Apple Watch utilizes two Apple-designed sensors: the Force Touch Sensor and the Heart Rate Sensor. The Force Touch sensor helps the watch determine the user’s intentions as they push on the screen, and the Heart Rate sensor uses a series of light sensors to determine vitals of the user. All five sensors work together to give a new and unique experience in a watch form factor.
movements and positions that smartphones are usually in do not require advanced monitoring, as they are resting in the palm of your hand. For Apple Watch, screen display orientation is not the only application these sensors are used for; they also determine movement of any kind, even if the watch is on standby. This is to help count steps and detect movement for letting users know they have not stood in a while. When exercising, the accelerometer and gyroscope send usable data to let the system know that that the user is doing more work than a brisk walk, and the software is able to track this data.
The accelerometer and the gyroscope are actually found in current smartphones. As is the case with the smartphones and wearables including the Apple Watch, the accelerometer and the gyroscope help determine orientation. There are actually three separate accelerometers in the Apple Watch— one for each axis, specifically the x-, y-, and z-axis. But, in most cases, these three sensors are combined and referred to as a single entity. In the case of the Apple Watch, and most small devices, the three accelerometers help detect movement in any direction. The gyroscope then measures the rate of rotation across these three axes.
Reading pressure is an interesting concept for a wearable device. The Apple Watch has a barometer implemented to read the pressure around the user. Similar to the accelerometer and the gyroscope, the barometer is widely used for the fitness aspect of the Apple Watch. The barometer can track elevation changes for a workout, which can occur when a user is running or biking and the path changes elevation. This can also help with step tracking when a user is climbing stairs. From the elevation change, the Apple Watch uses the data gained from the barometer to give an accurate calorie count, or accurate distance covered. The barometer can also read atmospheric changes between whether or not the user is indoors or outdoors allowing for the Apple Watch to give information and feedback allowing for productive suggestions.
For the Apple Watch, the data that the accelerometers and the gyroscope produce are read much more frequently than a smartphone. The range of
6
EEWEB FEATURE The engineers at Apple designed and implemented a Heart Rate Monitor to keep in line with the health-monitoring mission of the Apple Watch. Initially, it might seem reasonable to use an accelerometer to measure the vibration of someone’s pulse on a certain axis, but this might not give readings that would accurately portray the heart rate of the user wearing the device. Instead, the Apple Watch uses what is called photoplethysmography. Rather than using vibrations, this technology uses light as a means to measure heartrate. Blood reflects red light and absorbs green light, so green and infrared LEDs project light onto the user’s wrist while photodiode sensors actively read the amount of light reflected and absorbed from the LEDs. The LEDs flash hundreds of times per second in order to get an accurate count of heartbeats each minute. If the user’s body doesn’t pump blood aggressively, or the watch can’t get a reading then the Apple Watch software increases both LED brightness and sampling rate.
All five sensors [accelerometer, gyroscope, barometer, Force Touch sensor and Heart Rate sensor] work together to give a new and unique experience in a watch form factor.
Photo by Markort1312 (Own work) [CC BY-SA 4.0 (http://creativecommons. org/licenses/by-sa/4.0)], via Wikimedia Commons
Photo by thomersch (Own work) [CC BY 4.0 (http:// creativecommons.org/ licenses/by/4.0)], via Wikimedia Commons
7
SENSOR TECHNOLOGY
The Force Touch Sensor uses multiple different calculations to determine if the user just taps the surface or if the user is pressing on the surface.
8
The heartbeat monitor helps both in fitness and health monitoring as well as has some social benefits. Apple has implemented a heartbeat message between Apple Watch users that takes advantage of the heart rate sensor. Allowing an accurate heart rate sensor can be very beneficial to user’s health and gives unique functionality to a smartwatch. Apple has created what is called the Force Touch Sensor, which they started to implement into all of their devices including the trackpads in their laptops and iPhones. The Force Touch Sensor uses multiple different calculations to determine if the user just taps the surface or if the user is pressing on the surface. There is a force sensor implemented into the Apple Watch along with a lateral vibrator. When the user pushes down on the Apple Watch screen, a thin piezoelectric force sensor moves and from that movement, a voltage is created. The amount of force used generates a variable voltage, which is read by the
watch and is then converted by software to a force reading. The force reading is then used to determine whether the user wanted to do a tap or a press as well as controls the lateral vibrator. The lateral vibrator gives feedback to the user as to if a tap or a press is determined by increasing or decreasing the amount of vibration felt. Software has been developed that can provide different options to users based on a tap or a press of the watch. The Force Touch sensor allows a more immersive experience with the watch by allowing more control and giving more feedback. The Apple Watch is an attempt at stepping into the future smaller, wearable devices. Sensors make wearable devices that are much more practical when combined with the right software. With the many months of development, the software package implemented into the Apple Watch makes use of all the sensors helping the user receive a personalized experience while having the functionality of a smartphone.
http://www.cherrycorp.com
Your Circuit Starts Here. Sign up to design, share, and collaborate on your next project—big or small.
Schematics.com Click Here to Sign Up
SENSOR TECHNOLOGY
10
PRODUCT WATCH
ROHM
Sensor Platform Kit This sensor platform kit from ROHM showcases the company’s various sensors, demonstrating their flexibility and ease of use. The kit contains six expansion boards each with a different sensor on it such as hall sensor, analog, and light sensors. This provides an excellent starting place when integrating these sensors into your own project.
11
SENSOR TECHNOLOGY
Hardware Baseboard
Six Expansion Boards Six Sensor Expansion Boards • Digital ambient light sensor (BH1721FVC) (ROHM) • Analog ambient light sensor (BH1620FVC) (ROHM) • Omnipolar hall sensor (BU52011HFV) (ROHM)
Portable USB battery*
• Temperature sensor (BDE0600G) (ROHM)
Power Adaptors
• Analog UV sensor (ML8511) (LAPIS)
Quick Start Guide
• Baseboard for sensor platform
• Accelerometer + Magnetometer combo sensor (KMX61) (Kionix)
12
Portable USB Battery*
* The newer, less-expensive SENSEKIT2-EVK-101 from ROHM is now available without USB battery.
PRODUCT WATCH
Specs The baseboard has an FTDI chip on it, so the user can unplug the baseboard from the USB battery and plug directly into their computer. Using a PuTTY terminal at 9600 baud, the user gets a VT-100 terminal that shows the actual values of the ambient light, or whatever the sensor is measuring. Along with the analog ambient light sensor and hall sensor, the sensor kit includes a digital ambient light sensor, a UV sensor, an accelerometer and magnetometer combo sensor, as well as a temperature sensor. The kit provides an easy way to see each sensor’s capabilities and how easily they can be integrated into other projects. ROHM has created a Github account, with the address on the Quick Start Guide, where they have posted all of the design files, both the hardware and the firmware, for this entire kit. If you’re looking for small form factor and easy-to-use sensors, the ROHM sensor platform kit is a great first step to finding what you need.
Watch Video Click below to watch a demonstration of the ROHM sensor platform kit:
CLICK 13
CLIHERE
MYLINK
SENSOR TECHNOLOGY
Crouzet
Level Control Relays Available from
16
PRODUCT WATCH
HSN
ENRM
ENR
The Level Control Relays from Crouzet are typically used to control liquid levels in applications where fluid is being moved, monitored, or otherwise included in the system. Crouzet level control relays work by taking input from two level sensors, such as float switches, submersible probes, or capacitive sensors, and uses the feedback from those sensors to determine if the pump needs to turn on. The pump can be used for emptying or filling, and certain models include a time delay function. This time delay prevents the relay from toggling on and off due to waves or ripples in the liquid tripping the sensors.
17
SENSOR TECHNOLOGY
Specs Level control with Crouzet relays utilizes float switches, capacitive sensing, or immersed probes to toggle the internal relay, which controls power to the pumps and valves. This controlled filling and emptying prevents pumps from running dry, which often results in downtime to repair or replace the pump. Crouzet’s ENR is a single output level controller that can be configured to pump up or down and relies on submerged probes. The pumping action and sensitivity is set from the front of the unit. For filling or pumping up, the relay turns on to start the pump once the liquid drops below the probe; for emptying, it turns on when the liquid level reaches the probe. The ENRM adds multiple probe sensitivity ranges and a time delay when sensing a single level. The time delay can be set to delay turning the relay on or off once the appropriate liquid level is reached. This allows any waves to settle out and ensures pumping does not turn on or off too soon. The HNM is similar to the ENRM, but includes a second relay. This second relay can be used to control other functions or to indicate the status of the pump to a PLC or other system controller.
18
PRODUCT WATCH
Hardware 1 3
Operating Mode
2
Sensitivity Level
4
Time Delay
Crouzet HNM
Watch Video For more information on these and other Crouzet level control relays, visit OnlineComponents.com. To watch a video overview of the onlinecomponents.com Crouzet Level Control Relays, click below:
CLICK 19
SENSOR TECHNOLOGY
Sensing the
Future
ams’ Plans to Shape the World with Sensor Solutions
Interview with Thomas Stockmeier COO of ams
20
INDUSTRY INTERVIEW
T
he world around us is changing. Technology has increasingly become more integrated into
our surroundings to offer users a seamless operating experience with everyday devices. At the heart of this transformation are sensors; along with interface ICs and algorithms, sensors are integral in the intercommunication between the user and the device. For ams, an Austrian-based sensor solutions company, sensor solutions will take smart applications to the next level. The company’s highly differentiated product offerings are optimized for the most demanding and challenging applications, furthering the push towards a seamless interface between humans and technology. EEWeb spoke with Thomas Stockmeier, COO of ams, about the company’s broad sensor offering, how they will integrate with the Internet of Things, and some new exciting applications for sensor solutions.
21
SENSOR TECHNOLOGY
Tell us about ams as a company. What is the range of sensor products that you offer? Around three years ago, ams began transforming from a specialized analog IC company towards being the sensor and sensor solution company. Last year, we reorganized the company along product competencies. We have focused on two primary market segments: consumer, communication, and computing— which comprises two thirds of our business—and automotive, industry, and medical—which comprises one third of our business. All of our segments show strong growth, with the consumer segment taking the lead at the moment. We gave ourselves the mission to “shape the world with sensor solutions.” For us, this includes the sensor, the sensor interface IC, along with the algorithms and the software that is needed. So there is a high value proposition with our products. If you look into the technical competencies, our biggest segment is optical sensors, which are used predominantly for ambient light sensing, proximity sensing, gesture recognition, and bio sensing for health vitals and statistics. However, we also have a wide
22
range of other sensor solutions. Our company’s growth is mostly organic, but we also add competencies and market segments through acquisitions in accordance with our long-term strategy.
How will the rise of the Internet of Things affect the sensor industry? The Internet of Things is a broad term. It originally came from the industrial area where machines become more intelligent and communicate with each other. This boosts the number of sensors needed in industrial automation, but it also requires sensors to be more rugged, reliable, and longer lasting for all types of demanding applications. This is the distilled version of the Internet of Things. Another vision for the IoT is with smart homes. The smart home contains sensors that communicate with each other to recognize when a person or group of people walks into a room, and adjusts the room settings to their preferences. The IoT has certainly put a lot of wind under the wings of sensor technologies.
INDUSTRY INTERVIEW With your background in wireless as well as power management, how does your analog competence give you an advantage in the sensor world? At the end of the day, all these sensors provide an analog signal that must be generated at very low power consumption with a very high signalto-noise ratio, and then converted to a digital signal. ams has decades of analog experience, which puts us in a strong position. When you look into connectivity, you will find that there is a lot of digital content in there, but there is always an analog front-end, such as how you manage the antenna and how you manage the power. It is not easy to acquire these competencies, and ams is proud to have over 500 engineers on staff with deep knowledge in sensors, sensor ICs, wireless communication, and power.
In what ways does ams provide customized sensor solutions to its customers? When we look into the different market segments, such as the consumer space, we have customers that require very specific forms, shapes, and combinations of different sensors that fit their needs. We have platform technologies from which we derive the specific sensor solutions. In the automotive, industrial, and medical industries, it is common to have a customer that needs specific devices. In some cases, the customer comes to us with a specification and we build the sensor and the sensor interface according to these specifications, like a classic ASIC business model. We also have standard products that we can adapt, if needed, to precisely fit the customer’s needs – whether it is a package adaptation, or
23
SENSOR TECHNOLOGY
if it has special functions needed for the product. A majority of our business is targeted to meeting the specific needs of customers—ranging from very high to low volumes. And we have a whole variety of business models to accommodate our customers. There are no two customers that are the same. But, of course, we’re also selling standard products in very significant numbers.
As devices are becoming more connected, and there are more sensors implemented in devices, what are some of the new applications that you anticipate down the road? In the consumer space, there are certain trends that don’t go away—for example, every smartphone will need a proximity sensor, ambient light sensor, and microphone. Then there are sensors that may or may not be adopted by consumers in the long term, things like environmental sensors—gas, pressure, humidity, temperature—and biosensors. If we look at developing countries where the infrastructure is relatively weak, there is still a relatively large infrastructure for wireless capability in the smartphone area. Having a biosensor that goes
24
beyond the simple fitness function into a more serious medical application can really provide help to people in need. These sensors can send vital health data to doctors over long distances, who can determine if the patient needs immediate medical attention or not. These applications are very meaningful to the user and will definitely be widely adopted. Of course, biosensors will also greatly impact health status and associated health care costs in all other countries, as well. In the smart home area, we will see a great change in how lighting is arranged in homes and offices. ams has started to develop sensors that can adjust the color temperature and intensity in LED lights. Sensors can detect when the user walks into a room, and change the light settings to the individual’s preferences. The smart home will also contain more sensors that monitor air quality and human presence, which will all be connected by sensor hubs that adjust individual rooms. These sensors must have a friendly user interface so the consumer can fully utilize the sensor’s capabilities. One more example of new applications is the change in the heat, water, and gas metering business towards ultrasoundbased sensors. These sensors are much
INDUSTRY INTERVIEW more accurate and can detect even small leaks and then provide feedback to the user by wireless communication, thereby greatly contributing to conservation of precious natural resources.
What is ams doing to address the specific needs of these markets and applications and to enable those applications that are not quite possible right now? We have a well-designed strategy and road-mapping process that anticipates what our customer and market needs will be over the next few years. This roadmap contains the elements of markets, products, and technologies, all interconnected with each other, and identifies the needs for our own development and what we need to acquire. One of the major requirements is that sensors still need to become much smaller, more reliable, easier to use, and even more cost-effective.
the sensor and sensor IC into one wafer. Any type of wafer scale technology will allow us to achieve these goals and make the sensors very small, reliable, and rugged. We have pioneered a CMOS-compatible through-silicon via technology, which we first applied to the medical imaging area. However, recently we announced an optical sensor solution that has the sensor on top, the CMOS circuit underneath, and the TSV that connects this chip directly to the customer’s flex-substrate. It is the smallest—and in particular the lowest height—solution at the moment. It’s a great example of how we are shaping the world with sensor solutions.
There is one major technology trend that we actively pursue as an IDM, and that is that we monolithically integrate
25
SENSOR TECHNOLOGY
26
TECH SERIES
Addressing the Need for
Ultra-small AMBIENT LIGHT SENSORS
in Wearable Products By Dave Moon Senior Product Marketing Manager (US), ams http://www.ams.com www.ams.com
In today’s wearable health and fitness market, where consumer electronic backlight displays continue to get thinner, having an ambient light sensor (ALS) capable of being integrated into the thinnest backlight displays is becoming ever more important to designers of these devices. The proliferation of cell phones and the demand for better user experiences has driven a high adoption rate of ALS in touchscreen smartphones. In these display management applications, automatically controlling the backlight intensity with an ALS ensures the best possible user experience while extending battery life.
27
SENSOR TECHNOLOGY
However, one of the main challenges associated with making an ALS for the evolving wearables market, is that the ALS device must have an extremely thin form factor as it is usually mounted directly onto the actual flex PCB of the touch panel display. Additionally, the sensor’s accuracy and sensitivity should also be robust enough to allow for mounting behind inked glass. Light sensor technology has been around since the 1950s, and has evolved from the inception of simple photodiodes and phototransistors to intelligent opto-sensing solutions, which offer a much higher level of integration, lower
Figure 1. Smartwatch block diagram
28
operating power, and inclusion of noise immune digital bus interfaces. These modern day ambient light sensor solutions incorporate photodiodes, analog-to-digital converters (ADC), control logic for interrupt persistency and thresholds events, and a fast-mode I2C digital interface. The digital interface and interrupt capability makes it well suited for use in microcontroller- and processor-based applications such as wearables and smartwatches. As shown in Figure 1, ALS sensors are connected through a digital I2C interface to an applications processor in the smartwatch block-diagram.
TECH SERIES The Photopic and Silicon Response As with most consumer electronic devices, including wearable products, cost-effectiveness has become a key factor. Therefore, a light sensor made with a CMOS photodiode offers the effective solution. However, the spectral responsivity of CMOS silicon is between 300nm and 1100nm, and peaks at around 700nm in the infrared (IR) region. As shown in Figure 2, the human eye responds to light in the 390- to 750nm-wavelength range. As seen in Figure 3, the visible region that the human eye responds to light encompasses a small portion of the region of the photodiodes response.
Figure 2. Visible light spectrum
The challenge of making a robust ALS is getting it to see the same 390-750nm wavelengths that the human eye sees without responding to wavelengths in the 300-390nm ultraviolet and 750-1100nm infrared wavelengths. ams’ TSL2584TSV light-to-digital sensor views ambient light just like the human eye sees light. It utilizes a verysensitive analog front-end (AFE) with a patented dual-diode architecture to transform light intensity into a digital count value. A broadband photodiode responsive to visible and infrared is used in conjunction with an infrared-
Figure 3. Silicon responsiveness and the photopic response
ams’ TSL2584TSV light-to-digital sensor views ambient light just like the human eye sees light.
29
SENSOR TECHNOLOGY
only responsive photodiode and the two photodiode channel responses are mathematically subtracted via a lux equation on a micro-controller through the digital I²C interface. Ambient light level illuminance in lux is derived using an empirical formula to approximate the human eye response. The TSL2584TSV is shown in Figure 4.
Figure 4. TSL2584TSV
To optimize this ALS solution, the TSL2584TSV includes an on-chip photopic infrared-blocking interference filter that rejects unwanted UV and IR producing a near-photopic response. This produces a highly accurate lux measurement irrespective of glass transmissivity, even when mounted behind very dark opaque glass. Through advanced filter deposition technology ams produces a more accurate and repeatable photopic filter than other filters offered in the market. This photopic filter virtually has no temperature or humidity variation and is deposited directly onto the silicon. The TSL2584TSV spectral responsivity is illustrated in Figure 5.
The Need for TSV Technology
Figure 5. TSL2584TSV spectral response
30
With the advantage of having inhouse wafer fabrication expertise, through-silicon via (TSV) packaging technology has been adopted by ams for advanced light sensor technology. TSV technology eliminates the use of wire bonds and provides a direct connection from the device I/Os to a solder ball as shown in Figure 6.
TECH SERIES The small package size of the TSV package technology addresses the small form factor size requirement in wearable products. The TSV package technology, which has been developed and qualified by ams, enables the design and production of radically improved IC packages that are smaller and offer better device performance. As seen in Figure 4, the TSL2584TSV ALS has a very small package size of 1.145 x 1.66mm with a height of 0.32mm, which is approximately half the size of competing devices and makes it the world’s smallest ALS. The TSV technology utilizes an etched via through the TSL2584 silicon wafer. Tungsten is deposited into these etched cavities, a Backside Re-Distribution
Layer (BRDL) is deposited from the via to the planned solder ball location, then SAC305 (Sn96.5Ag3.0Cu0.5 alloy composition) or similar Pb-free solder balls are affixed which results in an overall package height of 0.32mm. Removing the wirebonds and routing the signal directly down through a via channel constructed during the silicon manufacturing process results in an overall package height reduction, as seen in Figure 7. Additionally, without a bond wire connecting the IC to the package, interconnect inductance is minimized. Another key feature of this TSV package is that it is offered in a glassless package, which helps to further reduce the overall z-height compared to chip-scale packages. Since there is no
The TSV technology utilizes an etched via through the TSL2584 silicon wafer.
Figure 6. Through-silicon via packaging technology
31
SENSOR TECHNOLOGY
Figure 7. Reducing package height by removing the wirebonds
actual glass material included in the TSV package, not only is the z-height reduced but this type of glassless package is ideally suited for use in a different product to enable UV detection when paired with UV pass filters. Device reliability performance is also significantly improved with the TSV package because it minimizes the corrosion effects due to humidity exposure and enhances temperaturecycling performance. The TSV package has interconnects internal to the package, unlike some chip-scale packages that require metal edge connections, thus improving reliability of the TSL2584TSV to a Moisture Sensitivity Level-1 standard rating, making it suitable for higher moisture environments. The photopic interference filters deposited on the TSL2584TSV are quite dense, are extremely durable and have highly scratch resistance characteristics, similar to the glass used in chip-scale and MEMS packaging. The spectral response of the photopic filter has no degradation or spectral shifting after highly accelerated stress testing because its filter characteristics are not sensitive to Temperature and Humidity variations.
32
Future Outlook The wearables market is in its embryonic market state with a mere 24-million smartwatches and fitness band shipments in 2014. In a recent report from BI Intelligence, this market is projected to grow at as much as 35% CAGR to 135-million units by 2018. As the wearables market continues to evolve, offering reduced size, accurate, and high sensitivity ALS solutions such as the TSL2584TSV enables designers of wearable devices such as smart watches and fitness bands, to easily integrate ambient light sensors into the thinnest backlight displays. Improved accuracy and sensitivity performance allows for mounting behind inked glass while automatically controlling the backlight intensity and ensuring the best user experience. The ultra-small size of the TSL2584TSV provides developers with increased design flexibility as its footprint is less than 2mm2 and has a height of only 0.32 mm and overall a robust and effective solution.
For Further Information ams AG Tel:+43 (0) 3136 500 info@ams.com clickhereforemail www.ams.com clickhereforweb
MYLINK
M o v i n g To w a r d s a
David Elien VP of Marketing & Business Development, Cree, Inc.
Clean Energy
Let There Be
LIGHT
FUTURE
How Cree reinvented the light bulb
— Hugo van Nispen, COO of DNV KEMA
Cutting Edge
SPICE
Modeling
MCU Wars 32-bit MCU Comparison
+
Cutting Edge Flatscreen Technologies
+
New LED Filament Tower
View more EEWeb magazines— Click Here Click here
Power Developer O ct o b er
201 3
From Concept to
Reality
Sierra Circuits:
Designing for
Durability
A Complete PCB Resource
Wolfgang Heinz-Fischer Head of Marketing & PR, TQ-Group
TQ-Group’s Comprehensive Design Process
Freescale and TI Embedded Modules
+
Ken Bahl CEO of Sierra Circuits
PLUS: The “ Ground ” Myth in Printed Circuits
+
+
PCB Resin Reactor
ARM Cortex Programming
Low-Power Design Techniques