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Atmel has announced the production release of its Maxtouch range of capacitive touchscreen controllers, capable of supporting an unlimited number of simultaneous touches with a refresh rate of 250Hz.

Atmel’s Maxtouch technology platform supports the development of touchscreens surpassing 10in with full zoom, rotate, handwriting and shape-recognition functionality.

The first device in the range, the MXT224, has 224 nodes that allow it to accurately report the positions of unlimited, simultaneous touches and it can completely redraw the screen every 4ms.

The MXT224’s large number of nodes and fast performance make it suitable for advanced touchscreen functionality, such as rejection of unintended touches, stretch/pinch and rotate gestures, handwriting and shape recognition such as face detection on mobile phones, mobile internet devices (MID) and netbook screens.

By integrating the entire capacitive sensing circuitry on-chip, these Maxtouch products provide a fully integrated single-chip solution without the need for external components to support the capacitive sensing, minimising the cost and PCB footprint requirements.

Multiple MXT224 touchscreen solutions can be used to provide smaller interspatial distances between touches on larger screens.

The MXT224 is able to support the use of a stylus for drawing or signature capture and character recognition, thanks to its 80:1 signal-to-noise ratio (SNR) and fast refresh rate.

A high SNR is critical for the accurate reporting of adjacent or weak signals, and allows for precise reporting in noisy environments such as products with noise coupled from radio transceivers, LCD displays and battery chargers.

Solutions without a suitably high SNR consume more power and decrease their response time with extra filtering and processing in an attempt to extract a weak signal from a high noise environment.

In contrast, according to Atmel, the nearest competing off-the-shelf touchscreen solution has half as many nodes as the MXT224, a screen refresh rate of only 83Hz (66 per cent slower) and an SNR of only 25:1 (66 per cent less).

Maxtouch also offers advanced noise suppression algorithms to provide end products with the immunity against coupled noise issues.

By combining Atmel’s Charge Transfer and Xmega technologies, Atmel’s engineering teams have produced an optimal and scalable architecture that enables smart processing of a capacitive touch image to accurately regenerate and report the user’s interaction with the touchscreen.

The unlimited number of touches possible with Atmel’s Maxtouch technology is the result of its mutual capacitive sensor design, combined with Atmel’s Charge Transfer method of signal acquisition.

Unlike self capacitance technologies that sense individual rows or columns leaving ambiguity in reported multi-touch positions, mutual capacitance sensors create a matrix of independent capacitive sensing nodes at the intersections of these rows and columns.

Using Atmel’s Maxtouch technology, each of these nodes are independently scanned within the matrix accurately sensing the position of an unlimited number of touches and delivering smooth movement in any location of the screen.

The processing efficiency provided by the Xmega microcontroller CPU allows the chip to ignore unintentional activity such as facial touch when on a call with a mobile phone.

Atmel said that this capability, combined with the ability to collect the charge image in near theoretical times, allows the Maxtouch products to demonstrate extraordinary performance.

The MXT224 integrates Atmel’s single-cycle RISC AVR core with 32 registers and two on-chip DSP engines that process the X and Y positions on the touchscreen.

An event system and peripheral DMA controller off-load all inter-peripheral communications and data transfer operations from the CPU, freeing it up for post processing of the sensor image.

This architecture enables the simultaneous processing of 224 nodes at 250Hz, while consuming less than 5mW.

The MXT224 product is the first in a range of capacitive sensing controller solutions that eliminate the need for external components to support the capacitive sensing, thereby minimising cost and reducing PCB footprint requirements.

It is available now in a 5mm x 5mm BGA package.

Additional Maxtouch solutions will be introduced in the fourth quarter of 2009 and 2010.

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