QT110-D_技术文档

QProx™ QT110 / QT110H

C^HARGE-T^RANSFERT^OUCHS^ENSOR

! Less expensive than many mechanical switches

! Projects a ‘touch button’ through any dielectric

! Turns small objects into intrinsic touch sensors

! 100% autocal for life - no adjustments required

! Only one external part required - a 1¢ capacitor

! Piezo sounder direct drive for ‘tactile’ click feedback

! LED drive for visual feedback

Vdd

Out

1

2

3

4

8

7

6

5

Vss

Sns2

Sns1

Gain

! 2.5 to 5V 20µA single supply operation

! Toggle mode for on/off control (strap option)

! 10s or 60s auto-recalibration timeout (strap option)

! Pulse output mode (strap option)

! Gain settings in 3 discrete levels

! Simple 2-wire operation possible

Opt1

Opt2

! HeartBeat™ health indicator on output

! Active Low (QT110), Active High (QT110H) versions

APPLICATIONS -

! Light switches

! Industrial panels

! Appliance control

! Security systems

! Access systems

! Pointing devices

! Elevator buttons

! Toys & games

The QT110 / QT110H charge-transfer (“QT’”) touch sensor is a self-contained digital IC capable of detecting near-proximity or touch. It

will project a sense field through almost any dielectric, like glass, plastic, stone, ceramic, and most kinds of wood. It can also turn

small metal-bearing objects into intrinsic sensors, making them respond to proximity or touch. This capability coupled with its ability to

self calibrate continuously can lead to entirely new product concepts.

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

switch or button may be found; it 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.

The IC requires only a common inexpensive capacitor in order to function. A bare piezo beeper can be connected to create a ‘tactile’

feedback clicking sound; the beeper itself then doubles as the required external capacitor, and it can also become the sensing

electrode. An LED can also be added to provide visual sensing indication. With a second inexpensive capacitor the device can

operated in 2-wire mode, where both power and signal traverse the same wire pair to a host. This mode allows the sensor to be wired

to a controller with only a twisted pair over long distances.

Power consumption is under 20µA in most applications, allowing operation from Lithium cells for many years. In most cases the power

supply need only be minimally regulated.

The IC’s RISC core employs signal processing techniques pioneered by Quantum; these are specifically designed to make the device

survive real-world challenges, such as ‘stuck sensor’ conditions and signal drift. Even sensitivity is digitally determined and remains

constant in the face of large variations in sample capacitor C_Sand electrode C_X. No external switches, opamps, or other analog

components aside from C_Sare usually required.

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 interface. The Quantum-pioneered HeartBeat™ signal is also included, allowing a host controller to

monitor the health of the QT110 continuously if desired. By using the charge transfer principle, the IC delivers a level of performance

clearly superior to older technologies in a highly cost-effective package.

AVAILABLE OPTIONS

T_A

SOIC

8-PIN DIP

0⁰C to +70⁰C

-40⁰C to +85⁰C

QT110-S

QT110H-S

QT110-IS

QT110H-IS

QT110-D

QT110H-D

-

Quantum Research Group Ltd

R1.01/0106

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 single low cost, non-critical capacitor is

required for operation.

+2.5 to 5

SENSING

ELECTRODE

1

Vdd

2

3

4

7

5

6

OUT

SNS2

GAIN

SNS1

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

with

a

conventional output drive and power supply

C_s

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).

OPT1

OPT2

10nF

C_x

Vss

OUTPUT=DC

TIMEOUT=10 Secs

TOGGLE=OFF

GAIN=HIGH

8

1.1 BASIC OPERATION

The QT110 employs short, ultra-low duty cycle bursts of

charge-transfer cycles to acquire its signal. Burst mode

permits power consumption in the low 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

Cs is thus non-critical; as it drifts with temperature, the

threshold algorithm compensates for the drift automatically.

A simple circuit variation is to replace Cs with a bare piezo

sounder (Section 2), which is merely another type of

capacitor, albeit with a large thermal drift coefficient. If C_piezo

is in the proper range, no other external component is

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

an inexpensive ceramic capacitor connected in parallel with

it. 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.

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 QT110 (Figure 1-3). A 14-bit

single-slope switched capacitor ADC includes both the

required QT charge and transfer switches in a configuration

that provides direct ADC conversion. The ADC is designed to

dynamically optimize the QT burst length according to the Option pins allow the selection or alteration of several special

rate of charge buildup on Cs, which in turn depends on the features and sensitivity.

values of Cs, Cx, and Vdd. Vdd is used as the charge

reference voltage. Larger values of Cx cause the charge

1.2 ELECTRODE DRIVE

transferred into Cs to rise more rapidly, reducing available

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

resolution; as a minimum resolution is required for proper

a direct result, the sense electrode can be connected to

operation, this can result in dramatically reduced apparent

either SNS1 or SNS2 with no performance difference. In both

gain. Conversely, larger values of Cs reduce the rise of

cases the rule Cs >> Cx must be observed for proper

differential voltage across it, increasing available resolution

operation. The polarity of the charge buildup across Cs

by permitting longer QT bursts. The value of Cs can thus be

during a burst is the same in either case.

increased to allow larger values of Cx to be tolerated (Figures

It is possible to connect separate Cx and Cx’ loads to SNS1

and SNS2 simultaneously, although the result is no different

than if the loads were connected together at SNS1 (or

SNS2). It is important to limit the amount of stray capacitance

on both terminals, especially if the load Cx is already large,

for example by minimizing trace lengths

4-1, 4-2, 4-3 in Specifications, rear).

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

the threshold level ratiometrically with respect to absolute

load, and does so dynamically at all times.

and widths so as not to exceed the Cx

Figure 1-2 2-wire operation, self-powered (QT110 only)

load specification and to allow for a

larger sensing electrode size if so

desired.

+

SENSING

+3V

ELECTRODE

22µF10V AL

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

1

Vdd

CMOS

GATE

2.2k

Tw isted

pair

2

3

4

7

5

6

OUT

SNS2

GAIN

SNS1

C_s

desired

location.

Multiple

touch

OPT1

10nF

electrodes can be used, for example to

create a control button on both sides of

an object, however it is impossible for the

sensor to distinguish between the two

touch areas.

C_x

OPT2

Vss

8

- 2 -

1.3 ELECTRODE DESIGN

Figure 1-3 Internal Switching & Timing

ELECTRODE

1.3.1 E^LECTRODEG^{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

Result

SNS2

C_s

Start

C_x

Done

a

3-dimensional surface or object.

Sensitivity is related to electrode

surface area, orientation with respect

to the object being sensed, object

composition, and the ground coupling

quality of both the sensor circuit and

the sensed object.

SNS1

Charge

Amp

If a relatively large electrode surface is

desired, and if tests show that the

electrode has more capacitance than

the QT110 can tolerate, the electrode

can be made into a sparse mesh (Figure 1-4) having lower

Cx than a solid plane. Sensitivity may even remain the same,

as the sensor will be operating in a lower region of the gain

curves.

1.3.3 V^IRTUALC^APACITIVEG^ROUNDS

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 1-5), 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 1-5) 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 connections, then a ‘virtual capacitive ground’ may

be required to increase return coupling.

Figure 1-4 Mesh Electrode Geometry

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

QT110’s own circuit ground to:

(1) A nearby piece of metal or metallized housing;

(2) A floating conductive ground plane;

(3) A nail driven into a wall when used with small

electrodes;

(4) A larger electronic device (to which its output might be

connected anyway).

1.3.2 K^IRCHOFF’^SC^URRENTL^AW

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 Kirchoff’s law with

regard to hardwired circuits, it applies equally to capacitive

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 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.

Figure 1-5 Kirchoff's Current Law

C_X2

Sense Electrode

SENSOR

C_X1

C_X3

Su rro u nd in g e nviro nm e n t

- 3 -

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 1-6 Shielding Against Fringe Fields

1.3.5.1 Increasing Sensitivity

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.

Sensitivity can often be increased by using a bigger

electrode, reducing panel thickness, or altering panel

composition. Increasing electrode size can have diminishing

returns, as high values of Cx will reduce sensor gain (Figures

4-1 ~ 4-3). Also, 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. The panel or other intervening material can be

made thinner, but again there are diminishing rewards for

doing so. Panel material can also be changed to one having

a higher dielectric constant, which will help propagate the

field through to the front. Locally adding some conductive

material to the panel (conductive materials essentially have

an infinite dielectric constant) will also help dramatically; for

example, adding carbon or metal fibers to a plastic panel will

greatly increase frontal field strength, even if the fiber density

is too low to make the plastic bulk-conductive.

Sense

wire

Sense

wire

Unshielded

Electrode

Shielded

Electrode

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.

Table 1-1 Gain Setting Strap Options

Gain

Tie Pin 5 to:

None

High

Pin 6

Medium

Low

Pin 7

1.3.4 F^IELDS^HAPING

The electrode can be prevented from sensing in undesired

directions with the assistance of metal shielding connected to

circuit ground (Figure 1-6). For example, on flat surfaces, the

field can spread laterally and create a larger touch area than

desired. To stop field spreading, it is only necessary to

surround the touch electrode on all sides with a ring of metal

connected to circuit ground; the ring can be on the same or

opposite side from the electrode. The ring will kill field

spreading from that point outwards.

1.3.5.2 Decreasing Sensitivity

In some cases the QT110 may be too sensitive, even on low

gain. In this case gain can be lowered further by any of a

number of strategies: making the electrode smaller,

connecting a very small capacitor in series with the sense

lead, or making the electrode into a sparse mesh using a

high space-to-conductor ratio (Figure 1-4). A deliberately

added Cx capacitor can also be used to reduce sensitivity

according to the gain curves (see Section 4).

If one side of the panel to which the electrode is fixed has

moving traffic near it, these objects can cause inadvertent

detections. This is called ‘walk-by’ and is caused by the fact

that the fields radiate from either surface of the electrode

equally well. Again, shielding in the form of a metal sheet or

foil connected to circuit ground will prevent walk-by; putting a

small air gap between the grounded shield and the electrode

will keep the value of Cx lower and is

encouraged. In the case of the QT110, the

sensitivity is low enough that 'walk-by' should not

be a concern if the product has more than a few

millimeters of internal air gap; if the product is

very thin and contact with the product's back is a

concern, then some form of rear shielding may be

required.

Intermediate levels of gain (e.g. between 'medium' and 'low'

can be obtained by a combination of jumper settings with one

or more of the above strategies.

Figure 2-1 Drift Compensation

Signal

Hysteresis

Threshold

1.3.5 S^ENSITIVITY

Reference

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

Output

- 4 -

The QT110 employs

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

threshold levels.

a hysteresis dropout below the

2 - QT110 SPECIFICS

2.1 SIGNAL PROCESSING

The QT110 processes all signals using 16 bit math, 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.

2.1.3 M^AXO^N-D^URATION

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.

2.1.1 D^RIFTC^OMPENSATIONA^LGORITHM

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.

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

timeout durations available via strap option: 10 and 60

seconds.

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.

2.1.4 D^ETECTIONI^NTEGRATOR

It is desirable to suppress detections generated by electrical

noise or from quick brushes with an object. To accomplish

Table 2-1 Output Mode Strap Options

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.

Tie

Max On-

Duration

Pin 3 to:

Pin 4 to:

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.

Vdd

Gnd

Vdd

Gnd

Vdd

10s

60s

10s

DC Out

Toggle

Pulse

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.

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 18ms apart, so that the slowest reaction time possible

is 75+18+18+18 or 129ms and the fastest possible is 54ms,

depending on where in the initial burst interval the contact

first occurred. The response time will thus average 92ms.

2.1.2 T^HRESHOLDC^ALCULATION

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 automatically recomputed in real time so

that it is never in error.

2.1.5 F^ORCEDS^ENSORR^ECALIBRATION

The QT110 has no recalibration pin; a forced recalibration is

accomplished only when the device is powered up. However,

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.

Note that most 8051-based micros have only a weak pullup

drive capability and will require true CMOS buffering. Any

74HC or 74AC series gate can directly power the QT110, as

can most other microprocessors.

Figure 2-2 Powering From a CMOS Port Pin

PORT X.m

0.01µF

CMOS

microcontroller

Vdd

PORT X.n

OUT

QT110

Vss

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.

- 5 -

other circuit. Since Out is normally high, a pulldown resistor

will create negative HeartBeat pulses (Figure 2-3) 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 OUTPUT FEATURES

The QT110 / QT110H 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.

QT110H: Same as QT110 but inverted logic (use a pull-down

resistor instead of a pull-up etc.)

2.2.1 DC M^ODEO^UTPUT

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

the output is active-low (QT110) or active-high (QT110H)

upon detection. The output will remain active for the duration

of the detection, or until the Max 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.

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

2-4, the microprocessor 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.

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 2-5).

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

and 60 seconds.

2.2.2 T^OGGLEM^ODEO^UTPUT

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.

2.2.5 P^IEZOA^COUSTICD^RIVE

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

sounder immediately after a detection is made; the tone lasts

for a nominal 75ms to create a reassuring ‘tactile feedback’

sound.

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

When a timeout occurs, the sensor recalibrates but leaves

the output state unchanged.

2.2.3 P^ULSEM^ODEO^UTPUT

The sensor will drive most common bare piezo ‘beepers’

directly using an H-bridge drive configuration for the highest

possible sound level at all supply voltages; H-bridge drive

effectively doubles the supply voltage across the piezo. The

piezo is connected across pins SNS1 and SNS2. This drive

operates at a nominal 4kHz frequency, a common resonance

point for enclosed piezo sounders. Other frequencies can be

obtained upon special request.

This generates

a pulse of 75ms duration (QT110 -

negative-going; QT110H - positive-going) 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.

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

mode.

If desired a bare piezo sounder can be directly adhered to

the rear of a control panel, provided that an acoustically

resonant cavity is also incorporated to give the desired sound

level.

2.2.4 H^EARTB^EAT™ O^UTPUT

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.

Since piezo sounders are merely high-K ceramic capacitors,

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

metal disc will act as the sensing electrode. Piezo transducer

capacitances typically range from 6nF to 30nF (0.006µF to

0.03µF) 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 more if Cx is large.

QT110: 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

Figure 2-3

Figure 2-4

Using a micro to obtain HB pulses in either output state

(QT110 or QT110H)

Getting HB pulses with a pull-down resistor (QT110 shown;

use pull-up resistor with QT110H)

+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

- 6 -

conditions. Only if very fast, radical temperature swings are

expected will a higher quality capacitor be required, for

example polycarbonate, PPS film, or NPO/C0G ceramic.

Figure 2-5 Eliminating HB Pulses

GATE OR

MICRO INPUT

2

3

4

7

5

6

3.2 PIEZO SOUNDER

CMO S

OUT

SNS2

GAIN

SNS1

The use of a piezo sounder in place of Cs is described in the

previous section. Piezo sounders have very high,

uncharacterized thermal coefficients and should not be used

if fast temperature swings are anticipated.

C_o

100pF

OPT1

OPT2

3.3 OPTION STRAPPING

The option pins 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 tied low.

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 used

to provide an audible confirmation of functionality if desired,

or, it can be suppressed by placing a non-critical 1M to 2M

ohm bleed resistor in parallel with the resonator. The resistor

acts to slowly discharge the resonator, preempting the

occurrence of the harmonic-rich step (Figure 2-6).

The Gain input is designed to be floated for sensing one of

the three gain settings. It should never be connected to a

pullup resistor or tied to anything other than Sns1 or Sns2.

Table 2-1 shows the option strap configurations available.

Figure 2-6 Damping Piezo Clicks with Rx

With the resistor in place, an almost inaudible clicking sound

may still be heard, which is caused by the small charge

buildup across the piezo device during each burst.

+2.5 to 5

SENSING

ELECTRODE

2.2.6 O^UTPUTD^RIVE

1

The QT110’s `output is active low (QT110) or active high

(QT110H) and can source 1mA or sink 5mA of non-inductive

current. If an inductive load is used, such as a small relay,

the load should be diode clamped to prevent damage.

Vdd

2

3

4

7

5

6

OUT

SNS1

GAIN

SNS2

OPT1

OPT2

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, 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.

R

C

x

Vss

8

3.4 POWER SUPPLY, PCB LAYOUT

The power supply can range from 2.5 to 5.0 volts. At 3 volts

current drain averages less than 20µA in most cases, but can

be higher if Cs is large. Interestingly, large Cx values will

actually decrease power drain. Operation can be from

batteries, but be cautious about loads causing supply droop

(see Output Drive, previous section).

QT110: 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).

As battery voltage sags with use or fluctuates slowly with

temperature, the IC will track and compensate for these

changes automatically with only minor changes in sensitivity.

QT110H: This part is active-high, so it works in reverse to

that described above.

If the power supply is shared with another electronic system,

care should be taken to assure that the supply is free of

digital spikes, sags, and surges which can adversely affect

the device. The IC will track slow changes in Vdd, but it can

be affected by rapid voltage steps.

3 - CIRCUIT GUIDELINES

3.1 SAMPLE CAPACITOR

if desired, the supply can be regulated using a conventional

low current regulator, for example CMOS regulators that have

nanoamp quiescent currents. Care should be taken that the

regulator does not have a minimum load specification, which

almost certainly will be violated by the QT110's low current

requirement.

Charge sampler Cs can be virtually any plastic film or high-K

ceramic capacitor. Since the acceptable Cs range is

anywhere from 10nF to 30nF, the tolerance of Cs can be the

lowest grade obtainable so long as its value is guaranteed to

remain in the acceptable range under expected temperature

- 7 -

Since the IC operates in a burst mode, almost

all the power is consumed during the course of

each burst. During the time between bursts the

sensor is quiescent.

Figure 2-7 ESD Protection

+2.5 to 5

C1

+

3.4.1 M^EASURINGS^UPPLYC^URRENT

10µF

R

e2

Measuring average power consumption is a

fairly difficult task, due to the burst nature of

the device’s operation. Even a good quality

RMS DMM will have difficulty tracking the

relatively slow burst rate.

1

D

1

Vdd

2

3

4

7

5

6

SENSING

ELECTRODE

OUT

SNS2

R

e1

e3

D

2

The simplest method for measuring average

current is to replace the power supply with a

large value low-leakage electrolytic capacitor,

for example 2,700µF. 'Soak' the capacitor by

connecting it to a bench supply at the desired

operating voltage for 24 hours to form the

electrolyte and reduce leakage to a minimum.

Connect the capacitor to the circuit at T=0,

making sure there will be no detections during

OPT1

OPT2

GAIN

SNS1

C

s

Vss

8

small. The added diodes shown (1N4150, BAV99 or

equivalent low-C diodes) will shunt the ESD transients away

from the part, and Re1 will current limit the rest into the

QT110's own internal clamp diodes. C1 should be around

10µF if it is to absorb positive transients from a human body

model standpoint without rising in value by more than 1 volt.

If desired C1 can be replaced with an appropriate zener

diode. Directly placing semiconductor transient protection

devices or MOV's on the sense lead is not advised; these

devices have extremely large amounts of parasitic C which will

swamp the IC.

the measurement interval; at T=30 seconds measure the

capacitor's voltage with a DMM. Repeat the test without a

load to measure the capacitor's internal leakage, and

subtract the internal leakage result from the voltage droop

measured during the QT110 load test. Be sure the DMM is

connected only at the end of each test, to prevent the DMM's

impedance from contributing to the capacitor's discharge.

Supply drain can be calculated from the adjusted voltage

droop using the basic charge equation:

✁VC

t

i =

Re1 should be as large as possible given the load value of

Cx and the diode capacitances of D1 and D2. Re1 should be

low enough to permit at least 6 timeconstants of RC to occur

during the charge and transfer phases.

where C is the large supply cap value, t is the elapsed

measurement time in seconds, and ∆V is the adjusted

voltage droop on C.

Re2 functions to isolate the transient from the Vdd pin;

values of around 1K ohms are reasonable.

3.4.2 ESD ^PROTECTION

In cases where the electrode is placed behind a dielectric

panel, the IC will be protected from direct static discharge.

However, even with a panel, transients can still flow into the

electrode via induction, or in extreme cases, via dielectric

breakdown. Porous materials may allow a spark to tunnel

right through the material; partially conducting materials like

'pink poly' will conduct the ESD right to the electrode. Testing

is required to reveal any problems. The device does have

diode protection on its terminals which can absorb and

protect the device from most induced discharges, up to

20mA; the usefulness of the internal clamping will depending

on the dielectric properties, panel thickness, and rise time of

the ESD transients.

As with all ESD protection networks, it is crucial that the

transients be led away from the circuit. PCB ground layout is

crucial; the ground connections to D1, D2, and C1 should all

go back to the power supply ground or preferably, if

available, a chassis ground connected to earth. The currents

should not be allowed to traverse the area directly under the

IC.

If the device is connected to an external circuit via a cable or

long twisted pair, it is possible for ground-bounce to cause

damage to the Out pin; even though the transients are led

away from the IC itself, the connected signal or power ground

line will act as an inductor, causing a high differential voltage

to build up on the Out wire with respect to ground. If this is a

possibility, the Out pin should have a resistance Re3 in

series with it to limit current; this resistor should be as large

as can be tolerated by the load.

ESD dissipation can be aided further with an added diode

protection network as shown in Figure 2-7, in extreme cases.

Because the charge and transfer times of the QT110 are

relatively long, the circuit can tolerate very large values of Re,

more than 100k ohms in most cases where electrode Cx is

- 8 -

4.1 ABSOLUTE MAXIMUM SPECIFICATIONS

Operating temp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . as designated by suffix

Storage temp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -55^OC to +125^OC

V^DD. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.5 to +6.5V

Max continuous pin current, any control or drive pin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ±20mA

Short circuit duration to ground, any pin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . infinite

Short circuit duration to V^DD, any pin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . infinite

Voltage forced onto any pin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.6V to (Vdd + 0.6) Volts

4.2 RECOMMENDED OPERATING CONDITIONS

V^DD. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +2.5 to 5.5V

Supply ripple+noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20mV p-p max

Load capacitance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0 to 20pF

Cs value . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10nF to 30nF

4.3 AC SPECIFICATIONS Vdd = 3.0, Ta = recommended operating range

Parameter

Description

Min

Typ

Max

Units

Notes

T^RC

T^PC

T^PT

T^BS

T^BL

T^R

Recalibration time

550

2

ms

µs

Charge duration

Transfer duration

2

µs

Burst spacing interval

Burst length

75

ms

kHz

ms

µs

0.5

7

Response time

129

4

F^P

Piezo drive frequency

Piezo drive duration

Pulse output width on Out

Heartbeat pulse width

T^P

75

300

T^PO

T^HB

4.4 SIGNAL PROCESSING

Description

Min

Typ

Max

Units

Notes

Threshold differential, high gain

Threshold differential, medium gain

Threshold differential, low gain

Hysteresis

3.1

4.7

6.25

50

%

Note 1

Note 2

%

Consensus filter length

4

samples

ms/level

secs

Positive drift compensation rate

Negative drift compensation rate

Post-detection recalibration timer duration

750

75

10

60

Note 3

Note 1: Of absolute full scale signal

Note 2: Of signal threshold

Note 3: Strap option.

- 9 -

4.5 DC SPECIFICATIONS

Vdd = 3.0V, Cs = 10nF, Cx = 5pF, T^A= recommended range, unless otherwise noted

Parameter

Description

Min

Typ

Max

Units

Notes

V^DD

I^DD

Supply voltage

2.45

5.25

V

µA

V/s

V

Supply current

20

V^DDS

V^IL

Supply turn-on slope

Low input logic level

High input logic level

Low output voltage

High output voltage

Input leakage current

Load capacitance range

Min shunt resistance

Acquisition resolution

Sensitivity - high gain

Sensitivity - medium gain

Sensitivity - low gain

100

2.2

Required for proper startup

OPT1, OPT2

0.8

0.6

V^HL

V^OL

V^OH

I^IL

V

OPT1, OPT2

V

OUT, 4mA sink

OUT, 1mA source

OPT1, OPT2

Vdd-0.7

0

V

±1

30

µA

pF

✡

C^X

I^X

500K

Resistance from SNS1 to SNS2

A^R

14

bits

pF

S[1]

S[2]

S[3]

1

1.5

3

Refer to Figures 4-1 through 4-3

Preliminary Data: All specifications subject to change.

Figure 4-1 High Gain Sensitivity

and Range @ Vdd = 3V

Figure 4-2 Medium Gain Sensitivity

and Range @ Vdd = 3V

3.0

4.0

Cx=30pF

25pF

2.5

2.0

1.5

1.0

0.5

25pF

20pF

3.0

2.0

1.0

20pF

10pF

5pF

10pF

5pF

0pF

Valid operating range

10

20

30

10

20

30

Cs, nF

Figure 4-3 Low Gain Sensitivity

and Range @ Vdd = 3V

8.0

6.0

4.0

2.0

Cx=30pF

25pF

20pF

10pF

5pF

0pF

30

Valid operating range

10

20

Cs, nF

- 10 -

Package type: 8pin Dual-In-Line

Millimeters

Inches

Max

SYMBOL

Min

Max

Notes

Min

Notes

a

A

6.096

7.62

7.112

8.255

10.922

7.62

-

0.24

0.3

0.28

0.325

0.43

0.3

M

m

Q

P

9.017

7.62

Typical

BSC

0.355

0.3

Typical

BSC

0.889

0.254

0.355

1.397

2.489

3.048

0.381

3.048

-

0.035

0.01

0.014

0.055

0.098

0.12

0.015

0.12

-

L

0.559

1.651

2.591

3.81

-

0.022

0.065

0.102

0.15

-

L1

F

Typical

BSC

Typical

BSC

R

r

S

3.556

4.064

7.062

9.906

0.381

0.14

0.16

0.3

S1

Aa

x

7.62

0.3

8.128

0.203

0.32

0.008

0.39

0.015

Y

Package type: 8pin SOIC

Millimeters

Inches

Max

SYMBOL

Min

Max

Notes

Min

Notes

M

W

Aa

H

h

4.800

5.816

3.81

4.979

6.198

3.988

1.728

0.762

1.27

0.189

0.229

0.15

0.196

0.244

0.157

0.068

0.01

0.05

0.019

0.04

0.01

0.03

8º

1.371

0.101

1.27

0.054

0.004

0.050

0.014

0.02

D

L

BSC

0.355

0.508

0.19

0.483

1.016

0.249

0.762

8º

E

e

0.007

0.229

0º

ß

0.381

0º

Ø

- 11 -


型号：	QT110-D
厂家：	ETC
描述：	IC-QPROX SENSOR IC- QPROX传感器\n 传感器
文件：	总12页 (文件大小：207K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

QT110-D [ETC]

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