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QTouchADC

Atmel's Long-Range Proximity Sensing Solution
QTouchADC is Atmel's newest sensing algorithm that is implemented by oversampling a standard SAR ADC. The QTouch® devices charge a sense electrode of unknown capacitance to a known potential. The electrode is typically a copper area on a PCB (could be any conductive material, including ITO). QTouchADC only requires 1-series resistor and 1-pin per channel. No other external components are required. Compared with standard QTouch technology, QTouchADC offers faster acquisition times with shorter burst lengths, resulting in lower power consumption.

In the initial state, an amount of charge is built-up on an untouched sensor to set the sensor's reference level. As the finger makes contact with the sensor, it couples with the electric field of the sensor. This results in a drop of that sensor's charge – since a portion of that charge is drained off through the finger to ground. Further charge transfers (conversions) from that sensor result in a reduced signal level compared to the untouched state. If the difference between the reference level and the signal level is greater than the user-determined threshold (your delta), a touch is detected.

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QTouchADC can be set up to do physical touch sensing (where the finger makes contact with the sensor) or tuned to do proximity sensing (where the hand only needs to couple with the sensor's e-field). Guidelines for effective proximity can be found in the QTAN0087: Proximity Design Guide.

Signal processing in the decision logic makes QTouch technology robust and reliable, eliminating false detections caused by environmental noise.

Supports Multiple Button Types
QTouch sensors can drive single or multiple channels. When you're using multiple buttons, you can set each button for an individual sensitivity level. You can also use buttons of different sizes and shapes to meet both functional and aesthetic requirements.

Prevents False Touch Detections
When several touch buttons are close together, an approaching finger changes the signal level around more than one button. Atmel's patented Adjacent Key Suppression (AKS™) uses an iterative technique to repeatedly measure the capacitance change on each key, compare the results and determine which key the user intended to touch. AKS™ then suppresses or ignores signals from all other buttons, when the signal from the selected key remains above the threshold value. This prevents false touch detections on adjacent keys. AKS is selectable by the system designer.

Lowers Cross-Sensor Interference
For excellent electromagnetic compatibility, QTouch sensors use spread-spectrum modulation and sparse, randomized charging pulses with delays between bursts. Individual pulses can be as short as 5% or less of the intra-burst pulse spacing. The benefits of this approach include lower cross-sensor interference, reduced RF emissions and susceptibility, and low power consumption.

These devices feature automatic drift compensation, to account for slow changes due to component ageing or varying environmental conditions. They have a dynamic range of several decades and do not require coils, oscillators, RF components, special cabling or numerous discrete parts. QTouch technology presents a simple, robust, elegant and affordable engineering solution for your touch designs.