Mouse sensor technology, still evolving and here to stay
So commonplace is touch as a natural human interface, that it has found its way into PC peripherals, including the mouse, keyboard and standalone track pad. But for all the benefit that an intuitive touch screen provides with the right applications, more intensive user input such as typing or editing is generally more accurate and typically faster using a physical keyboard.
The latest touch screen devices to hit the market are tablets, slates, netbook convertibles and to a lesser extent, notebooks. Some may think these touch computing platforms will signal the obsolescence of the ubiquitous computer mouse, but this is not likely. Tablets are ideal for browsing the internet, watching videos, and reading, but the lack of a mechanical keyboard makes them more suited as content consumption devices. As with mobile phones, the virtual keyboard and associated user interface is not as easy to use when generating any significant amount of content.
This is evident by the fact that docking stations are sold with tablets that connect to traditional mice and keyboards. Computer touch screens, albeit of the resistive type, have been in existence for decades and have coexisted with the mouse and other peripherals. As touch technology migrates to multi-touch capacitive, the mouse and keyboard will remain the most efficient means of input and therefore will continue to be around for many years to come. With that foundation, this article will provide an overview of the evolution of mouse technology and will explore the latest innovations in surface coverage, power-consumption, integration and wireless connectivity.
It started with surface coverage
The first commercially viable LED-based optical mouse changed the computing world, as it displaced the mechanical ball mouse, along with the mouse pads they required to aid in smooth operation. The non-mechanical optical mouse was able to track more accurately and at a much higher resolution.
Figure 1: LED-Based optical navigation system.
As innovative as the LED optical navigation engine was, users soon realized that it could not track well on very smooth surfaces. To solve that problem, the next generation optical navigation engine was invented by replacing the LED with a vertical cavity surface emitting laser or VCSEL. The coherent nature of the collimated laser light, along with the specular optics, allowed this sensor to track on more surfaces compared to the LED-based mouse sensor.
Figure 2: Laser-based navigation engine tracks on more surfaces.
The PC mouse has become so commonplace that, when it doesn’t simply work on all surfaces, the user is surprised. This is particularly evident when attempting to use either an LED or standard laser mouse on glass. The ability to track on glass has long been heralded as the pinnacle of optical navigation technology. It has taken many years of development, but the first track-on-glass engine was market released in 2009 by Avago Technologies. Today, it remains the only such laser navigation technology with the highest level of combined surface coverage and tracking available.
Figure 3: Some laser-based mice can now track on glass.
The desktop goes mobile
Optical navigation technology has evolved to keep up with the way consumers use their computers. Today, users find themselves computing in remote locations where glass, granite and other reflective table top surfaces are present. Today, mobile computing platforms far exceed shipments of desktop PCs. While it was once thought that such trends would lead to a significant drop in mouse usage, unit volumes have actually enjoyed growth. Many users still prefer to carry a mouse to use, rather than using the built-in laptop track pad, because of improved responsiveness, accuracy, and immunity to false touches.
With mobility comes the need for long battery life. In the last two years, most of the major mouse manufacturers promote battery life as a selling feature because longer battery life appeals to the environmentally conscious consumer. To support the green effort, the optical navigation system must be capable of consuming less current and operate at lower supply voltages. At Avago, this is accomplished through patented or proprietary firmware powering inventive hardware and optical designs.
Another source of power reduction is the choice of LED illumination. Red LEDs have historically been used because the sensor’s pixel array was most sensitive at the 630nm wavelength. However, the red LED is not very efficient and contributed to shorter battery life of the mouse. IR LEDs (870nm) with lower forward bias voltage enable usage with lower supply voltages, and in turn, reduce the power consumption of the overall optical navigation solution. Both the IR LED and the mouse sensor can use the same 1.8V power supply. As an example of power-efficiency development, the Avago ADNS-2080/3000 navigation sensors offer over one year of operation with a single AA-sized battery.
Integration of key components
As technologies mature, the tendency is to vertically integrate more of the solution into a single IC to help reduce the overall size, complexity and power consumption. The earliest mouse sensor solutions consisted of a separate navigation sensor, illumination source (LED or laser) and lens. For corded mice, a separate USB MCU was also required to communicate to the host PC. And, for cordless mice, a separate MCU and radio was required. Over time, the packaged LED or laser was integrated into the sensor package, the USB MCU was integrated into the navigation sensor, and radio manufacturers combined the discrete MCU and radio.
Radio protocols
The choice between radio protocols depends on the desired performance, value and cost of the mouse. The use of 27MHz radios is largely being replaced by 2.4GHz proprietary technology, as the cost of the higher frequency standard has come down enough where the performance of the 2.4GHz outweighs the price premium. Both 27MHz and 2.4GHz radios require dongles to complete the wireless communication link to the host computer.
Bluetooth is another 2.4GHz option. As a standard protocol, a mouse equipped with a Bluetooth radio is able to communicate with all laptops with built-in Bluetooth without the need for a separate dongle. Bluetooth radios used to be the most expensive wireless solution but, the price has fallen to a point where it competes with 2.4GHz proprietary technology. A laser sensor with integrated Bluetooth, such as the Avago ADNS-7630 device, can greatly reduce problems with interoperability and pairing. Integrated solutions can also help to simplify dealing with the sensor/radio interface, and reduce power consumption.
Figure 4: Comparison of the wireless protocols most commonly used in cordless mice.
The computer mouse has evolved from the simple mechanical ball mouse to a device that contains some of the most sophisticated electronics found in consumer electronics today. The changing user environment has driven the development of innovations over the past decade, and will continue to do so. In fact, as Google TV and other digital living room technologies become more popular, 3D motion control devices, already available today may become more mainstream.
The choices between LED-based or laser-based sensors, wired or one of the three wireless protocols, and discrete solutions or vertically integrated, will result in various combinations of performance and cost. With all of these tools at their disposal, mouse manufacturers can offer a full spectrum of differentiated computer mice that appeal to every market segment.
Dennis Moy is marketing director, navigation interface division at Avago Technologies – www.avagotech.com
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