QT110-DG_技术文档

lQ

QT110

QTOUCH™ SENSOR IC

ꢀ Less expensive than many mechanical switches

ꢀ Projects a ‘touch button’ through any dielectric

ꢀ 100% autocal for life - no adjustments required

ꢀ No active external components

Vdd

Out

1

2

3

4

8

7

6

5

Vss

Sns2

Sns1

Gain

ꢀ Piezo sounder direct drive for ‘tactile’ click feedback

ꢀ LED drive for visual feedback

Opt1

Opt2

ꢀ 2.5 ~ 5V single supply operation

ꢀ 10µA at 2.5V - very low power drain

ꢀ Toggle mode for on/off control (via option pins)

ꢀ 10s or 60s auto-recalibration timeout (via option pins)

ꢀ Pulse output mode (via option pins)

ꢀ Gain settings in 3 discrete levels

ꢀ Simple 2-wire operation possible

ꢀ HeartBeat™ health indicator on output

ꢀ Pb-Free packages

APPLICATIONS -

ꢀ Light switches

ꢀ Industrial panels

ꢀ Appliance control

ꢀ Security systems

ꢀ Access systems

ꢀ Pointing devices

ꢀ Elevator buttons

ꢀ Consumer electronics

The QT110 charge-transfer (“QT’”) sensor IC is a self-contained digital IC used to implement near-proximity or touch sensors. It

projects sense fields through almost any dielectric, like glass, plastic, stone, ceramic, and wood. It can also turn small metal-bearing

objects into intrinsic sensors, making them respond to proximity or touch. This capability coupled with an ability to self-calibrate

continuously leads to entirely new product concepts.

The QT110 is designed specifically for human interfaces, like control panels, appliances, toys, lighting controls, or anywhere a

mechanical switch or button may be found; they may also be used for some material sensing and control applications provided that

the presence duration of objects does not exceed the recalibration timeout interval.

A piezo element can also be connected to create a feedback click sound.

This IC requires only a common inexpensive capacitor in order to function. Average power consumption is under 20µA in most

applications, allowing battery operation.

The QT110 employs digital signal processing techniques pioneered by Quantum, designed to make it survive real-world challenges,

such as ‘stuck sensor’ conditions and signal drift. Sensitivity is digitally determined for the highest possible stability. No external active

components are required for operation.

The device includes several user-selectable built-in features. One, toggle mode, permits on/off touch control for example for light

switch replacement. Another makes the sensor output a pulse instead of a DC level, which allows the device to 'talk' over the power

rail, permitting a simple 2-wire twisted-pair interface. Quantum’s unique HeartBeat™ signal is also included, allowing a host controller

to continuously monitor sensor health.

By using the charge transfer principle, the QT110 delivers a level of performance clearly superior to older technologies in a highly

cost-effective package.

AVAILABLE OPTIONS (Pb-FREE)

T_A

0⁰C to +70⁰C

-40⁰C to +85⁰C

SOIC

-

8-PIN DIP

QT110-DG

-

QT110-ISG

lq

QT110 R1.04/0405

Figure 1-1 Standard mode options

1 - OVERVIEW

The QT110 is a digital burst mode charge-transfer (QT) sensor

designed specifically for touch controls; it includes all hardware

and signal processing functions necessary to provide stable

sensing under a wide variety of changing conditions. Only a

few low cost, non-critical discrete external parts are required for

operation.

+2.5 ~ +5

1

R

E

Vdd

2

3

4

7

5

6

SENSING

OUT

SNS2

GAIN

SNS1

Figure 1-1 shows the basic QT110 circuit using the device,

with a conventional output drive and power supply

connections. Figure 1-2 shows a second configuration using a

common power/signal rail which can be a long twisted pair from

a controller; this configuration uses the built-in pulse mode to

transmit output state to the host controller (QT110 only).

ELECTRODE

OPT1

OPT2

Rs

Cs

C_x

2nF - 500nF

Vss

OUTPUT = DC

TIMEOUT = 10 Secs

TOGGLE = OFF

GAIN = HIGH

8

1.1 BASIC OPERATION

The QT110 employs low duty cycle bursts of charge-transfer

cycles to acquire its signal. Burst mode permits power

consumption in the low microamp range, dramatically reduces

EMC problems, 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.

1.2 ELECTRODE DRIVE

The internal ADC treats Cs as a floating transfer capacitor; as a

direct result, the sense electrode can in theory be connected to

either SNS1 or SNS2 with no performance difference.

However, the noise immunity of the device is improved by

connecting the electrode to SNS2, preferably via a series

resistor Re (Figure 1-1) to roll off higher harmonic frequencies,

both outbound and inbound.

The QT switches and charge measurement hardware functions

are all internal to the QT110 (Figure 1-3). A single-slope

switched capacitor ADC includes both the required QT charge

and transfer switches in a configuration that provides direct

ADC conversion. Vdd is used as the charge reference voltage.

In order to reduce power consumption and to assist in

discharging Cs between acquisition bursts, a 470K series

resistor Rs should be connected across Cs (Figure 1-1).

Larger values of Cx cause the charge transferred into Cs to

rise more rapidly, reducing available resolution; as a minimum

resolution is required for proper operation, this can result in

dramatically reduced apparent gain.

The rule Cs >> Cx must be observed for proper operation.

Normally Cx is on the order of 10pF or so, while Cs might be

10nF (10,000pF), or a ratio of about 1:1000.

It is important to minimize the amount of unnecessary stray

capacitance Cx, for example by minimizing trace lengths and

widths and backing off adjacent ground traces and planes so

as keep gain high for a given value of Cs, and to allow for a

larger sensing electrode size if so desired.

The IC is highly tolerant of changes in Cs since it computes the

signal threshold level ratiometrically. Cs is thus non-critical and

can be an X7R type. As Cs changes with temperature, the

internal drift compensation mechanism also adjusts for the drift

automatically.

The PCB traces, wiring, and any components associated with

or in contact with SNS1 and SNS2 will become touch sensitive

and should be treated with caution to limit the touch area to the

desired location.

Piezo sounder drive: The QT110 can drive a piezo sounder

after a detection for feedback. The piezo sounder replaces or

augments the Cs capacitor; this works since piezo sounders

are also capacitors, albeit with a large thermal drift coefficient.

If C_piezois in the proper range, no additional capacitor is

required. If C_piezois too small, it can simply be ‘topped up’ with a

ceramic capacitor in parallel. The QT110 drives a ~4kHz signal

across SNS1 and SNS2 to make the piezo (if installed) sound a

short tone for 75ms immediately after detection, to act as an

audible confirmation.

1.3 ELECTRODE DESIGN

1.3.1 ELECTRODE

G

EOMETRY AND

S

IZE

There is no restriction on the shape of the electrode; in most

cases common sense and a little experimentation can result in

a good electrode design. The QT110 will operate equally well

with long, thin electrodes as with round or square ones; even

random shapes are acceptable. The electrode can also be a

3-dimensional surface or object. Sensitivity is related to

electrode surface area, orientation with respect to the object

being sensed, object composition, and

Option pins allow the selection or alteration of several other

special features and sensitivity.

the ground coupling quality of both the

sensor circuit and the sensed object.

Figure 1-2 2-wire operation, self-powered

+

3.5 - 5.5V

1K

1.3.2 KIRCHOFF

’

S

C

URRENT

L

AW

10µF

Like all capacitance sensors, the QT110

relies on Kirchoff’s Current Law (Figure

1-5) to detect the change in capacitance

of the electrode. This law as applied to

capacitive sensing requires that the

sensor’s field current must complete a

loop, returning back to its source in

order for capacitance to be sensed.

Although most designers relate to

CMOS

LOGIC

Twisted

pair

1N4148

1

Vdd

SNS2

RE

2

3

4

7

5

6

SENSING

ELECTRODE

OUT

n-ch Mosfet

C_s

OPT1 GAIN

Rs

C_x

OPT2 SNS1

Vss

Kirchoff’s law with regard to hardwired

circuits, it applies equally to capacitive

8

LQ

2

QT110 R1.04/0405

field flows. By implication it requires that

the signal ground and the target object

must both be coupled together in some

manner for a capacitive sensor to

operate properly. Note that there is no

need to provide actual hardwired ground

connections; capacitive coupling to

ground (Cx1) is always sufficient, even if

the coupling might seem very tenuous.

For example, powering the sensor via an

isolated transformer will provide ample

ground coupling, since there is

Figure 1-3 Internal Switching & Timing

ELECTRODE

Result

SNS2

C_s

Start

C_x

Done

capacitance between the windings

and/or the transformer core, and from

the power wiring itself directly to 'local

earth'. Even when battery powered, just

the physical size of the PCB and the

object into which the electronics is

embedded will generally be enough to

couple a few picofarads back to local

earth.

SNS1

Charge

Amp

1.3.3 VIRTUAL

C

APACITIVE

G

ROUNDS

In some cases it may be desirable to increase sensitivity

further, for example when using the sensor with very thick

panels having a low dielectric constant.

When detecting human contact (e.g. a fingertip), grounding of

the person is never required. The human body naturally has

several hundred picofarads of ‘free space’ capacitance to the

local environment (Cx3 in Figure 1-3), which is more than two

orders of magnitude greater than that required to create a

return path to the QT110 via earth. The QT110's PCB however

can be physically quite small, so there may be little ‘free space’

coupling (Cx1 in Figure 1-3) between it and the environment to

complete the return path. If the QT110 circuit ground cannot be

earth grounded by wire, for example via the supply

Sensitivity can often be increased by using a bigger electrode,

reducing panel thickness, or altering panel composition to one

having a higher dielectric constant. Increasing electrode size

can have diminishing returns, as high values of Cx will reduce

sensor gain.

Increasing the electrode's surface area will not substantially

increase touch sensitivity if its diameter is already much larger

in surface area than the object being detected. Metal areas

near the electrode will reduce the field strength and increase

Cx loading and are to be avoided for maximal gain.

connections, then a ‘virtual capacitive ground’ may be required

to increase return coupling.

A ‘virtual capacitive ground’ can be created by connecting the

QT110’s own circuit ground to:

Ground planes around and under the electrode and its SNS

trace will cause high Cx loading and destroy gain. The possible

signal-to-noise ratio benefits of ground area are more than

negated by the decreased gain from the circuit, and so ground

areas around electrodes are discouraged. Keep ground,

power, and other signals traces away from the electrodes and

SNS wiring.

- A nearby piece of metal or metallized housing;

- A floating conductive ground plane;

- Another electronic device (to which its might be connected

already).

Free-floating ground planes such as metal foils should

maximize exposed surface area in a flat plane if possible. A

square of metal foil will have little effect if it is rolled up or

crumpled into a ball. Virtual ground planes are more effective

and can be made smaller if they are physically bonded to other

surfaces, for example a wall or floor.

The value of Cs has a minimal effect on sensitivity with these

devices, but if the Cs value is too low there can be a sharp

drop-off in sensitivity.

1.3.4 SENSITIVITY

The QT110 can be set for one of 3 gain levels using option pin

5 (Table 1-1). If left open, the gain setting is high. The

sensitivity change is made by altering the numerical threshold

level required for a detection. It is also a function of other

things: electrode size, 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 are all influences.

Figure 1-5 Kirchoff's Current Law

C

X2

Gain plots of the device are shown on page 9.

The Gain input should never be tied to anything other than

SNS1 or SNS2, or left unconnected (for high gain setting).

Sense Electrode

SENSOR

Table 1-1 Gain Strap Options

C

X1

Gain

High

Tie Pin 5 to:

Leave open

Pin 6

C

Medium

Low

X3

Surrounding environm ent

Pin 7

LQ

3

QT110 R1.04/0405

2.1.4 DETECTION

I

NTEGRATOR

2 - QT110 SPECIFICS

It is desirable to suppress detections generated by electrical

noise or from quick brushes with an object. To accomplish this,

the QT110 incorporates a detect integration counter that

increments with each detection until a limit is reached, after

which the output is activated. If no detection is sensed prior to

the final count, the counter is reset immediately to zero. In the

QT110, the required count is 4.

2.1 SIGNAL PROCESSING

The QT110 processes all signals using a number of algorithms

pioneered by Quantum. The algorithms are specifically

designed to provide for high 'survivability' in the face of all kinds

of adverse environmental changes.

2.1.1 DRIFT

C

OMPENSATION

A

LGORITHM

The Detection Integrator can also be viewed as a 'consensus'

filter, that requires four detections in four successive bursts to

create an output. As the basic burst spacing is 75ms, if this

spacing was maintained throughout all 4 counts the sensor

would react very slowly. In the QT110, after an initial detection

is sensed, the remaining three bursts are spaced about 20ms

apart, so that the slowest reaction time possible is

Signal drift can occur because of changes in Cx and Cs over

time. It is crucial that drift be compensated for, otherwise false

detections, non-detections, and sensitivity shifts will follow. Cs

drift has almost no effect on gain since the threshold method

used is ratiometric. However Cs drift can still cause false

detections if the drift occurs rapidly.

75+20+20+20 or 135ms and the fastest possible is 60ms,

depending on where in the initial burst interval the contact first

occurred. The response time will thus average about 95ms.

Drift compensation (Figure 2-1) is performed by making the

reference level track the raw signal at a slow rate, but only

while there is no detection in effect. The rate of adjustment

must be performed slowly, otherwise legitimate detections

could be ignored. The QT110 drift compensates using a

slew-rate limited change to the reference level; the threshold

and hysteresis values are slaved to this reference.

2.1.5 FORCED

S

ENSOR

R

ECALIBRATION

The QT110 has no recalibration pin; a forced recalibration is

accomplished only when the device is powered up. However,

the supply drain is so low it is a simple matter to treat the entire

IC as a controllable load; simply driving the QT110's Vdd pin

directly from another logic gate or a microprocessor port

(Figure 2-2) will serve as both power and 'forced recal'. The

source resistance of most CMOS gates and microprocessors is

low enough to provide direct power without any problems.

Almost any CMOS logic gate can directly power the QT110.

Once an object is sensed, the drift compensation mechanism

ceases since the signal is legitimately high, and therefore

should not cause the reference level to change.

The QT110's drift compensation is 'asymmetric': the reference

level drift-compensates in one direction faster than it does in

the other. Specifically, it compensates faster for decreasing

signals than for increasing signals. Increasing signals should

not be compensated for quickly, since an approaching finger

could be compensated for partially or entirely before even

touching the sense pad. However, an obstruction over the

sense pad, for which the sensor has already made full

allowance for, could suddenly be removed leaving the sensor

with an artificially elevated reference level and thus become

insensitive to touch. In this latter case, the sensor will

compensate for the object's removal very quickly, usually in

only a few seconds.

A 0.01uF minimum bypass capacitor close to the device is

essential; without it the device can break into high frequency

oscillation.

Option strap configurations are read by the QT110 only on

powerup. Configurations can only be changed by powering the

QT110 down and back up again; again, a microcontroller can

directly alter most of the configurations and cycle power to put

them in effect.

2.2 OUTPUT FEATURES

2.1.2 THRESHOLD

C

ALCULATION

The devices are designed for maximum flexibility and can

accommodate most popular sensing requirements. These are

selectable using strap options on pins OPT1 and OPT2. All

options are shown in Table 2-1.

Sensitivity is dependent on the threshold level as well as ADC

gain; threshold in turn is based on the internal signal reference

level plus a small differential value. The threshold value is

established as a percentage of the absolute signal level. Thus,

sensitivity remains constant even if Cs is altered dramatically,

so long as electrode coupling to the user remains constant.

Furthermore, as Cx and Cs drift, the threshold level is

OPT1 and OPT2 should never be left floating. If they are

floated, the device will draw excess power and the options will

not be properly read on powerup. Intentionally, there are no

pullup resistors on these lines, since pullup resistors add to

power drain if the pin(s) are tied low.

automatically recomputed in real time so that it is never in error.

The QT110 employs a hysteresis dropout below the threshold

level of 50% of the delta between the reference and threshold

levels.

2.2.1 DC MODE

O

UTPUT

The output of the device can respond in a DC mode, where the

output is active-low upon detection. The output will remain

active for the duration of the detection, or until the Max

The threshold setting is determined by option jumper; see

Section 1.3.4.

2.1.3 MAX

ON-DURATION

If an object or material obstructs the sense pad the

signal may rise enough to create a detection,

preventing further operation. To prevent this, the

sensor includes a timer which monitors detections.

If a detection exceeds the timer setting, the timer

causes the sensor to perform a full recalibration.

This is known as the Max On-Duration feature.

Figure 2-1 Drift Compensation

Signal

Hysteresis

Threshold

Reference

After the Max On-Duration interval, the sensor will

once again function normally, even if partially or

fully obstructed, to the best of its ability given

electrode conditions. There are two nominal

timeout durations available via strap option: 10 and

60 seconds. The accuracy of these timeouts is

approximate.

Output

LQ

4

QT110 R1.04/0405

Figure 2-2 Powering From a CMOS Port Pin

Figure 2-3 Damping Piezo Clicks with R

s

+2.5 ~ +5

PORT X.m

0.01µF

1

CMOS

RE

Vdd

2

3

4

7

5

6

SENSING

microcontroller

OUT

SNS1

GAIN

SNS2

ELECTRODE

Vdd

OPT1

OPT2

PORT X.n

OUT

QT110

Rs

C_x

Vss

8

On-Duration expires, whichever occurs first. If the latter occurs

first, the sensor performs a full recalibration and the output

becomes inactive until the next detection.

Piezo sounders have very high, uncharacterized thermal

coefficients and should not be used if fast temperature swings

are anticipated, especially at high gains. They are also

generally unstable at high gains; even if the total value of Cs is

largely from an added capacitor the piezo can cause periodic

false detections.

In this mode, two Max On-Duration timeouts are available: 10

and 60 seconds.

2.2.2 TOGGLE

M

ODE

O

UTPUT

The burst acquisition process induces a small but audible

voltage step across the piezo resonator, which occurs when

SNS1 and SNS2 rapidly discharge residual voltage stored on

the resonator. The resulting slight clicking sound can be greatly

reduced by placing a 470K resistor Rs in parallel with the

resonator; this acts to slowly discharge the resonator,

attenuating of the harmonic-rich audible step (Figure 2-3).

This makes the sensor respond in an on/off mode like a flip

flop. It is most useful for controlling power loads, for example in

kitchen appliances, power tools, light switches, etc.

Max On-Duration in Toggle mode is fixed at 10 seconds. When

a timeout occurs, the sensor recalibrates but leaves the output

state unchanged.

Note that the piezo drive does not operate in Pulse mode.

2.2.5 HEARTBEAT™ OUTPUT

Table 2-1 Output Mode Strap Options

The output has a full-time HeartBeat™ ‘health’ indicator

superimposed on it. This operates by taking 'Out' into a 3-state

mode for 350µs once before every QT burst. This output state

can be used to determine that the sensor is operating properly,

or, it can be ignored using one of several simple methods.

Tie

Pin 3 to:

Tie

Pin 4 to:

Max On-

Duration

Vdd

Gnd

Vdd

Gnd

Vdd

10s

60s

10s

DC Out

Toggle

Pulse

The HeartBeat indicator can be sampled by using a pulldown

resistor on Out, and feeding the resulting negative-going pulse

into a counter, flip flop, one-shot, or other circuit. Since Out is

normally high, a pulldown resistor will create negative

HeartBeat pulses (Figure 2-4) when the sensor is not detecting

an object; when detecting an object, the output will remain

active for the duration of the detection, and no HeartBeat pulse

will be evident.

2.2.3 PULSE

M

ODE

O

UTPUT

This mode generates a negative pulse of 75ms duration with

every new detection. It is most useful for 2-wire operation, but

can also be used when bussing together several devices onto

a common output line with the help of steering diodes or logic

gates, in order to control a common load from several places.

If the sensor is wired to a microcontroller as shown in Figure

2-5, the controller can reconfigure the load resistor to either

ground or Vcc depending on the output state of the device, so

that the pulses are evident in either state.

Max On-Duration is fixed at 10 seconds if in Pulse output

mode.

Electromechanical devices will usually ignore this short pulse.

The pulse also has too low a duty cycle to visibly activate

LED’s. It can be filtered completely if desired, by adding an RC

timeconstant to filter the output, or if interfacing directly and

only to a high-impedance CMOS input, by doing nothing or at

most adding a small non-critical capacitor from Out to ground

(Figure 2-6).

Note that the beeper drive does not operate in Pulse mode.

2.2.4 PIEZO

A

COUSTIC

D

RIVE

A piezo drive signal is generated for use with a piezo sounder

immediately after a detection is made; the tone lasts for a

nominal 95ms to create a ‘tactile feedback’ sound.

The sensor drives the piezo using an H-bridge configuration for

the highest possible sound level. The piezo is connected

across pins SNS1 and SNS2 in place of Cs or in addition to a

parallel Cs capacitor. The piezo sounder should be selected to

have a peak acoustic output in the 3.5kHz to 4.5kHz region.

2.2.6 OUTPUT

D

RIVE

The QT110’s output is active low ; it can source 1mA or sink

5mA of non-inductive current.

Care should be taken when the IC and the load are both

powered from the same supply, and the supply is minimally

regulated. The device derives its internal references from the

power supply, and sensitivity shifts can occur with changes in

Vdd, as happens when loads are switched on. This can induce

detection ‘cycling’, whereby an object is detected, the load is

turned on, the supply sags, the detection is no longer sensed,

Since piezo sounders are merely high-K ceramic capacitors,

the sounder will double as the Cs capacitor, and the piezo's

metal disc can even act as the sensing electrode. Piezo

transducer capacitances typically range from 6nF to 30nF in

value; at the lower end of this range an additional capacitor

should be added to bring the total Cs across SNS1 and SNS2

to at least 10nF, or possibly more if Cx is above 5pF

LQ

5

QT110 R1.04/0405

Figure 2-4

Getting HB pulses with a pull-down resistor

Figure 2-5

Using a micro to obtain HB pulses in either output state

+2.5 to 5

HeartBeat™ Pulses

1

PORT_M.x

2

3

4

7

5

6

Vdd

2

3

4

7

5

6

OUT

SNS2

GAIN

SNS1

OUT

SNS2

GAIN

SNS1

R

o

Ro

Microprocessor

OPT1

OPT2

OPT1

OPT2

PORT_M.y

Vss

8

the load is turned off, the supply rises and the object is

reacquired, ad infinitum. To prevent this occurrence, the output

should only be lightly loaded if the device is operated from an

unregulated supply, e.g. batteries. Detection ‘stiction’, the

opposite effect, can occur if a load is shed when Out is active.

to reduce stray loading (which will dramatically reduce

sensitivity).

2. Keep Cs, Rs, and Re very close to the IC.

3. Make Re as large as possible. As a test, check to be sure

that an increase of Re by 50% does not appreciably

decrease sensitivity; if it does, reduce Re until the 50%

test increase has a negligible effect on sensitivity.

The output of the QT110 can directly drive a resistively limited

LED. The LED should be connected with its cathode to the

output and its anode towards Vcc, so that it lights when the

sensor is active-low. If desired the LED can be connected from

Out to ground, and driven on when the sensor is inactive, but

only with less drive current (1mA).

4. Do not route the sense wire near other ‘live’ traces

containing repetitive switching signals; the sense trace will

pick up noise from them.

3.3 POWER SUPPLY, PCB LAYOUT


型号：	QT110-DG
厂家：	QUANTUM RESEARCH GROUP
描述：	QTOUCH⑩ SENSOR IC QTOUCH⑩传感器IC 传感器
文件：	总12页 (文件大小：382K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

QT110-DG [QUANTUM]

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