AT42QT1011 View Datasheet(PDF) - Atmel Corporation
Part Name
Description
Manufacturer
AT42QT1011 Datasheet PDF : 25 Pages
| |||
2. Overview of the AT42QT11
2.1 Introduction
The AT42QT1011 (QT1011) is a digital burst mode charge-transfer (QT™) sensor that is capable of detecting near-
proximity or touch, making it ideal for implementing touch controls.
With the proper electrode and circuit design, the self-contained digital IC will project a touch or proximity field to
several centimeters through any dielectric like glass, plastic, stone, ceramic, and even most kinds of wood. It can
also turn small metal-bearing objects into intrinsic sensors, making them responsive to proximity or touch. This
capability, coupled with its ability to self-calibrate, can lead to entirely new product concepts.
The QT1011 is designed specifically for human interfaces, like control panels, appliances, toys, lighting controls, or
anywhere a mechanical switch or button may be found. It includes all hardware and signal processing functions
necessary to provide stable sensing under a wide variety of changing conditions. Only a single low-cost capacitor is
required for operation.
2.2 Basic Operation
Figure 1-1 on page 4 and Figure 1-2 on page 4 show basic circuits.
The QT1011 employs bursts of charge-transfer cycles to acquire its signal. Burst mode permits power consumption
in the microamp range, dramatically reduces RF emissions, lowers susceptibility to EMI, and yet permits excellent
response time. Internally the signals are digitally processed to reject impulse noise, using a “consensus” filter which
requires four consecutive confirmations of a detection before the output is activated.
The QT switches and charge measurement hardware functions are all internal to the QT1011.
2.3 Electrode Drive
For optimum noise immunity, the electrode should only be connected to SNSK.
In all cases the rule Cs >> Cx must be observed for proper operation; a typical load capacitance (Cx) ranges from
5 – 20 pF while Cs is usually about 2 – 50 nF.
Increasing amounts of Cx destroy gain, therefore it is important to limit the amount of stray capacitance on both SNS
terminals. This can be done, for example, by minimizing trace lengths and widths and keeping these traces away
from power or ground traces or copper pours.
The traces and any components associated with SNS and SNSK will become touch sensitive and should be treated
with caution to limit the touch area to the desired location.
A series resistor, Rs, should be placed in line with SNSK to the electrode to suppress ESD and EMC effects.
2.4 Sensitivity
2.4.1
Introduction
The sensitivity on the QT1011 is a function of things like the value of Cs, electrode size and capacitance, electrode
shape and orientation, the composition and aspect of the object to be sensed, the thickness and composition of any
overlaying panel material, and the degree of ground coupling of both sensor and object.
2.4.2
Increasing Sensitivity
In some cases it may be desirable to increase sensitivity; for example, when using the sensor with very thick panels
having a low dielectric constant, or when the device is used as a proximity sensor. Sensitivity can often be increased
by using a larger electrode or reducing panel thickness. Increasing electrode size can have diminishing returns, as
high values of Cx will reduce sensor gain.
AT42QT1010 [DATASHEET]
5
9542I–AT42–05/2013
Share Link: 