1 Overview

The QT1101 is an easy to use, ten touch-key sensor IC

based on Quantum’s patented charge-transfer (‘QT’)

principles for robust operation and ease of design. This

device has many advanced features which provide for

reliable, trouble-free operation over the life of the product.

Burst operation: The device operates in ‘burst mode’. Each

key is acquired using a burst of charge-transfer sensing

pulses whose count varies depending on the value of the

reference capacitor Cs and the load capacitance Cx. In LP

mode, the device sleeps in an ultra-low current state

between bursts to conserve power. The keys signals are

acquired using three successive bursts of pulses:

Burst A: Keys 0, 1, 4, 5

Burst B: Keys 2, 3, 6, 7

Burst C: Keys 8, 9

Bursts always operate in A-B-C sequence.

Self-calibration: On power-up, all ten keys are

self-calibrated within 450ms typical to provide reliable

operation under almost any conditions.

Auto-recalibration: The device can time out and recalibrate

each key independently after a fixed interval of continuous

touch detection, so that the keys can never become ‘stuck

on’ due to foreign objects or other sudden influences. After

recalibration the key will continue to function normally. The

delay is selectable to be either 10s, 60s, or infinite

(disabled).

The device also auto-recalibrates a key when its signal

reflects a sufficient decrease in capacitance. I n this case the

device recalibrates after ~2 seconds so as to recover normal

operation quickly.

Drift compensation operates to correct the reference level

of each key slowly but automatically over time, to suppress

false detections caused by changes in temperature,

humidity, dirt and other environmental effects.

The drift compensation is asy mmetric. In the increasing

capacitive load direction the device drifts more slowly than in

the decreasing direction. In the increasing direction, the rate

of compensation is one count of signal per two seconds. In

the opposing direction, it is one count every 500ms.

Detection Integrator (DI) confirmation reduces the effects

of noise on the QT1101 outputs. The DI mechanism requires

consecutive detections over a number of measurement

bursts for a touch to be confirmed and indicated on the

outputs. In a like manner, the end of a touch (loss of signal)

has to be confirmed over a number of measurement bursts.

This process acts as a type of ‘ debounce’ against noise.

In normal operation, both the start and end of a touch must

be confirmed for six measurement bursts. In a special ‘Fast

Detect‘ mode (available via jumper resistors) (Tables 1.2 and

1.6), confirmation of the start of a touch requires only two

sequential detections, but confirmation of the end of a touch

is still six bursts.

Fast detect is only available when AKS is disabled.

Spread Spectrum operation: The bursts operate over a

spread of frequencies, so that external fields will have

minimal effect on key operation and emissions are very

weak. Spread spectrum operation works with the DI

mechanism to dramatically reduce the probability of false

detection due to noise.

Sync Mode: The QT1101 features a Sync mode to allow the

device to slave to an external signal source, such as a mains

signal (50/60Hz), to limit interference effects. This is

performed using the SYNC/LP pin. Sync mode operates by

triggering three sequential acquire bursts, in sequence

A-B-C from the Sync signal. Thus, each Sync pulse causes

all ten keys to be acquired.

Low Power (LP) Mode: The device features an LP mode for

microamp levels of current drain with a slower response

time, to allow use in battery operated devices. On detection

of touch, the device automatically reverts to its normal mode

and asserts the DETECT pin active to wake up a host

controller. The device remains in normal, full acquire speed

mode until another pulse is seen on its SYNC/LP pin, upon

which it goes back to LP mode.

AKS™ Adjacent Key Suppression is a patented feature

that can be enabled via jumper resistors. AKS works to

prevent multiple keys from responding to a single touch, a

common complaint about capacitive touch panels. This can

happen with closely spaced keys, or with control surfaces

that have water films on them.

AKS operates by comparing signal strengths from keys

within a group of keys to suppress touch detections from

those that have a weaker signal change than the dominant

one.

The QT1101 has two different AKS groupings of keys,

selectable via option resistors . These groupings are:

AKS operates in three groups of keys.

AKS operates over all ten keys.

These two modes allow the designer to provide AKS while

also providing for shift or function operations.

If AKS is disabled, all keys can operate simultaneously.

Outputs: The QT1101 has a serial output using one or two

wires, RS-232 data format, and automatic baud rate

detection. A simple protocol is employed.

The QT1101 operates in slave mode, i.e. it only sends data

to the host after receiving a request from the host.

An additional /CHANGE (state changed) signal allows the

use of the serial interface to be optimised, rather than being

polled continuously.

Simplified Mode: To reduce the need for option resistors,

the simplified operating mode places the part into fixed

settings with only the AKS feature being selectable. LP

mode is also possible in this configuration. Simplified mode

is suitable for most applications.

2

QT1101 R4.06/0806