Broadcom AMRI-3100, Optical Sensor for Ultra-slim Scrollwheel User guide

Brand: Broadcom

Model: AMRI-3100, Optical Sensor for Ultra-slim Scrollwheel

Type: User guide

AMRI-3100

Optical Sensor for Ultra-slim Scrollwheel with 5-way Switch

Design Guide

Introduction

Avago Technologies has been the industry leading supplier

of optical motion or navigation sensor used in optical

mouse. With its core technology in motion encoders,

Avago started out designing and selling classical optical

encoders and has progressed to designing and manu-

facturing high accuracy, ease of use, low cost and ultra

miniature optical encoders. With these technologies,

Avago has enabled designers to miniaturize their design

for portable handheld and mobile devices with excellent

performance.

This design guide is to provide the relevant information

on designing an ultra-thin optical scrollwheel integrated

with 5-way switch in conjunction with Avago’s AMRI-3100

optical sensor.

Features for Scrollwheel

• Scrolling feature integrated with four directional

switches and a center push button

• Z-height proﬁle of 2mm and above

• Typical 18.5 mm diameter

• Optional illumination ring (for z-height of 3mm or more)

• Two-channel Quadrature Output (ChA & ChB)

• 16 Cycles Per Revolution (CPR)

• 1.8V / 3.3V TTL/CMOS Logic Compatible Single-ended

Output (with optional component)

• Single 2.4V to 3.3V supply

• Simple Power Down feature (with optional component)

• Easy assembly, no signal adjustment required

• Customizable aesthetic design

• -15°C to 70°C operating temperature

• Ease of assembly

Applications

• Handheld electronic devices

• Mobile devices

• Digital cameras and camcorders

• Entertainment consoles

• Handheld GPS or navigation devices

• Portable audio and video players

• Photo printers

Operating Principle of Scrollwheel

AMRI-3100 combines an emitter and a detector in a single

surface mount package. When used with a codewheel

(CW) or code strip, the reﬂective sensor translates rotary

or linear motion into a two-channel digital output.

The light from the emitter that beams onto the rotating

code wheel placed underneath the dial of scrollwheel is

reﬂected onto the photo-detector IC. As the code wheel

Figure 1. Illustration on the scrollwheel operation

ChA

ChB

VCC

GND

Emitter

Detector

Processing

Circuitry

Code Wheel

Window

(Reﬂective)

Bar

(Non-Reﬂective)

AMRI - 3100

Figure 2. Functional block of AMRI-3100 optical sensor

rotates, an alternating pattern of light beams and shadows

which corresponds to the reﬂective and non-reﬂective

pattern of the code wheel falls onto the photodiodes to

generate the internal signals (A, compliment of A, B and

compliment of B). These signals are fed into the process-

ing circuitry part of the sensor to produce the ﬁnal outputs

in channel A (ChA) and channel B (ChB).

Block Diagram of Scrollwheel

Figure 3. Block diagram of Scrollwheel

Figure 4. Matrix Conﬁguration for Switches

Figure 3 illustrates the functional block diagram for a

scrollwheel with 5-way switch and light-emitting diode

(LED) illumination.

The illumination block as the name describe, is to provide

illumination to the scrollwheel through the illumination

ring located between the dial and the center push button.

It consists of the current limiting resistor (R1) and two

LEDs that diﬀuse light through the illumination ring.

The Sensor block is the most important block in terms of

the actual operation of converting motion (in this case dial

rotation) into quadrature output signals. The main com-

ponents are emitter, specular code wheel, optical encoder

or detector and the digital signal processing circuitry as

described in the previous section.

The Switches block consists of all the 5 tactile switches

for the 4-way directional navigation and the center push

button for selection. Normally metal dome switches

will be used for such application. The switch should be

connected to a common ground (GND_SW pin). For

this switch conﬁguration, 6 I/O pins are required for the

5 switches (see Figure 3). However, if the number of I/O

pins is a constraint, another type of conﬁguration, which

is the matrix conﬁguration, can be used. For matrix con-

ﬁguration, only 5 I/O pins are required as shown in Figure

4. Therefore, for scrollwheel with 5-way switches and il-

lumination, minimally there will be 11 pin outs (using the

matrix conﬁguration for switches).

Power Down Control block is an optional feature to

minimize current consumption to a few microampere

from a typical operating current of 7-10mA (without illu-

mination) or 30mA (with illumination). This feature is es-

pecially useful during stand-by mode when the device is

not in use (or active mode).Basically it is a switch to control

supply voltage (VCC) that goes into the AMRI-3100 to turn

it on when necessary and power down the sensor totally

when not in use. Normally for such application, a load

switch such as MIC94060 can be used.

Level Shifter block is an optional block used to convert

the output level at CHA and CHB from a default 3.3V to

1.8V to provide TTL/CMOS logic compatible single ended

output. The voltage level translator digital switch such

as ADG3242 can be used to provide such function to the

scrollwheel if necessary.

For scrollwheel with only the scroll function and 4-way

switch and a center button, minimally, 9 microcontroller

(MCU) ports required (VCC, GND, CHA, CHB and 5 ports for

switches - based on matrix conﬁguration).

Placement of Critical Optical Components

A. Placement of AMRI-3100 and Codewheel

Placement of the motion or navigation sensor on the

printed circuit board (PCB) or ﬂexible printed circuit (FPC)

is very important and critical to ensure good performance

and functionality of the scrollwheel. Figure 5 is the sensor

mounting guide obtained from datasheet of AMRI-3100

(refer to document number AV02-1468EN). The sensor

can be rotated at the dial rotation axis to suite the overall

design as shown with the rectangle dotted lines in Figure 6.

Do not rotate the sensor itself. Misplacement of the sensor

will result in bad scrollwheel performance (indicated

through its output signals) and unit mal-function, thus

positioning of AMRI-3100 sensor must be according to

Figure 5 and Figure 6.

2.18

5.49

18.7°

3.28

2.16

13.5 (CW OD)

9.35 (CW ID)

ChB

Vcc

ChA

Figure 5. Mounting Outline

Figure 6. Sensor Placement Options on PCB

Position as per

datasheet

Blue outline indicates other possible locations of sensor

ROP

Center of rotation

or Codewheel

ROP – optical radius (center line of codewheel)

≈ 0.2mm

(Avago

standard)

0.94mm



Reﬂective Optical

Center (ROC)

= CW

≈ R

− 1, R

≈ R

+ 1

Figure 7. Sensor Placement and CW Alignment

The reﬂective optical center (ROC) of AMRI-3100 is recom-

mended to be located at ROP of CW for even amount of

radial play which is L/2 each side. θ is the angle between

the line from center of rotation to ROC and the shorter

edge of the IC nearest to ROC. For the design published

in the datasheet, θ is 20.2°. The CW pattern has been

optimized base on:

ROP = 5.65mm;

CW Inner Diameter = 9.35mm

CW Outer Diameter = 13.5mm

This CW design can be used for dial size of 18 to 22mm of

the scrollwheel.

However, changes to ROP would require a new angle (θ)

value and a new CW pattern. The recommendation is for

the location and outline of AMRI-3100 be ﬁxed ﬁrst before

placing of other components onto the PCB to avoid per-

formance issues and potential issues with the redesign of

codewheels.

Codewheel Design

The spiral design of CW as shown in Figure 8 is a patented

design of Avago Technologies. Current material for the CW

is FNS bright PAT1 11LL from Lintec Corporation and the

black ink is of SG740 Series, Vinyl Urethane Resin two-part

reaction ink from Seiko Advance Ltd, has been demon-

strated to work well for the scrollwheels.

Thickness of CW depends on raw material thickness and

design. Nominal thickness is between 0.08 - 0.1mm. In

special case, there are customers designed it thinner (as

thin as 0.04mm). Comparatively, thicker CW provides

better handling during assembly than thinner. However,

additional layer of ﬁlm can be stacked behind it to increase

the total thickness if necessary.

Figure 8. Spiral Codewheel (CW) Design Figure 9. Illumination LEDs keep out region

B. Placement of Illumination LED

Being an optical sensor, the AMRI-3100 should be

prevented from stray light that falls onto it because any

unintended light source onto the AMRI-3100 could cause

noise to the IC and create abnormal output signal (for

example glitches) or at worst case may cause scrollwheel

to not function at all.

In the need of putting illumination LED, the LED should be

at least 3.5mm away from every edge of the AMRI-3100.

For side ﬁring LED, it should not be placed to shine toward

the AMRI-3100 IC even if it is placed outside the 3.5mm

region. The colors for the illumination LED are limited only

to Blue, Green and White. Other colors will aﬀect the IC

performance even it is place outside the 3.5mm region.

Do not place LED inside this region

PCB

Figure 10. Top View and Operation of Scrollwheel

Mechanical Structure of Scrollwheel

A. Basic Construction

Scrolling

4-way Click/

Switch

Center Click/

Button

Figure 11. Exploded View of Mechanical Structure

Rubber Pad

Wheel Deco

Wheel / Dial

UHMW sheet

Wheel Bracket

Center Button

Wheel Bottom

CW (refer to Avago)

PCB/FPC

(inclusive of

sensor & metal

dome switch)

Sub - assembly by Keypad maker

(Top Assembly)

PCB Supplier

(Bottom Assembly)

Example Design

Figure 12. Cross Section of Top Assembly

Sub-assembly by Keypad maker

(Top Assembly)

Rotation axis

of wheel

Button

center

Wheel / Dial

Sub Key

Wheel

Bottom

Wheel

Bracket

UMHW Sheet

Rubber Pad

Wheel Deco

The mechanical structure of the scrollwheel can be divided

into two portions, the top assembly and the bottom

assembly. The top assembly (consist of mostly plastic

parts) can be a sub-assembly provided by the keypad

maker. The design is quite similar to the standard keypad

sub-assembly, added with some rotating parts and can

be designed to be mounted either onto the PCB or the

customer casing.

The bottom assembly that consist mainly the PCB or FPC

and metal dome sheet attached onto it can be done by

PCB manufacturer. The AMRI-3100 sensor is layout and

mounted onto the PCB or FPC by the PCB reﬂow process.

Figure 13. Cross Section of Bottom Assembly

AMRI - 3100

sensor

PCB/ FPC

Rotation axis

of wheel

Wheel / Dial

Sub Key

of Keypad

Wheel

Bottom

Wheel

Bracket

UMHW Sheet

Wheel Deco

Stopper

Rubber Pad

Center

Button

Figure 14. Cross Section of AMRI-3100 and Scrollwheel

AMRI - 3100

PCB/ FPC

Metal Dome Sheet

From PCB Supplier

(Bottom Assembly)

B. Moving Structures

The rotating portion of the scrollwheel is mainly made

up of the Wheel, Wheel Bottom and CW. Adhesive glue

or heat staking can be used to attach the Wheel Bottom

to the Wheel. The CW is attached to the Wheel Bottom.

Wheel Bottom also provides a surface that is held down

by Wheel Bracket and thus preventing the moving parts

from being detached. Rotation is guided by Wheel

Bracket whereby it provides a base for the Wheel to slide

on. UHMW (Ultra High Molecular Weight) sheet is added

to provide smoother rotation. UHMW is a hi-tech, self-

lubricating anti-friction plastic that makes material and

surfaces slide eﬀortlessly.

Besides rotation, there is also vertical movement required

of the scrollwheel mechanical structure to enable clicking

of the 4-way switch. The Wheel Bracket and Rubber Pad

play an important role here (refer Figure 17). A protruding

structure of the bracket labeled as Stopper is recommend-

ed at the location adjacent to AMRI-3100 as to prevent the

CW from being scratched by excessive force when the

Wheel is depressed on the 4-way switch near the sensor

(refer to Figure 14 and Figure 15). For optimum perfor-

mance, please ensure that the condition below is fulﬁlled.

s < g < Z whereby

s – stroke of metal dome

g – gap between Stopper and PCB

Z – gap between CW and top plane of AMRI-3100

Figure 15. Position of Stopper on Wheel Bracket

45°

Preferred location for Stopper

on Wheel Bracket

AMRI - 3100

* Black dotted lines indicate Metal Dome switch locations

Figure 16 shows the cross section across A-A which is

directly across the sensor. Do note that the gap between

the CW and PCB has to be controlled to be within the

speciﬁcation published in the datasheet of the sensor.

If the gap is too large, some potential issues could be

missing pulse or/and out of speciﬁcation in the phase on

the quadrature output signals.

Figure 17 shows the cross section across the metal dome

at B-B instead of the sensor. The Rubber Pad that holds up

the Wheel Bracket to guide rotation is resting on the metal

dome. Four posts on the Rubber Pad are designed to sit

on top of the four metal domes for clicking. When the

metal dome switch is clicked or pressed, the metal dome

collapse causing vertical downward movement of Wheel

Bracket and Rubber Pad. Once the metal dome is released,

the bracket and pad will return to their original positions.

Figure 16. Cross Section across A-A in Figure 14

Wheel / Dial

Sub Key

Wheel

Bottom

AMRI-3100

PCB/ FPC

Refer to

AMRI-3100

datasheet for

gap size from

CW p to PCB

Wheel Deco

Screw

Gap 0.05 min

A-A (Bracket hold down by Wheel Deco with Screw, 4x)

Figure 17. Cross Section across B-B in Figure 14

B-B (Bracket hold up by metal dome, 4x)

Wheel Deco

Sub Key

of Keypad

Wheel

Bracket

Rubber Pad

Figure 18. Wheel Deco as Internal Bracket

B. Non-moving Structures

Wheel Deco is used to hold the Wheel Bracket and to

prevent it from being lifted and rotated. It can be mounted

onto the PCB or FPC or casing of device with screws (refer

Figure 16) or heat staking. Alternatively, it can also be

designed internally as internal bracket as shown in Figure

18 if it is not required to enhance aesthetic outlook on the

top surface of the scrollwheel.

Figure 19. Mounting of Center Button

Sensor

Sub Key

Wheel Bracket

Wheel Deco as internal bracket

Center

Button

Sub Key

Rubber Pad

Figure 20. Basic concept of Dust Protection Construction

Center

Button

Wheel / Dial

Sub Key

Wheel

Bottom

AMRI-3100

Minimal gap where

dust enters

PCB/ FPC

Wheel

Bracket

UHMW Sheet Wheel Deco

Rib from Rubber Pad

(all around the wheel)

No entry for dust

from side

Structure for reduction

of dust entry

Metal dome

sheet

The Center Button is attached to the Rubber Pad using glue

or adhesive. This construction is similar to normal keypad

construction and the designer’s logo can be placed on the

surface of the button. The gluing of the Center Button is

to prevent it from free movement that could cause rattling

of button due to vibration. It also helps ﬁx the position of

the Center Button to always keep the logo at its upright

position.

C. Protection

The recommended mechanical structure is designed

based on considerations to minimize dust entering the

scrollwheel through minimizing the possible paths of

entry and having protection structure along the entry

path to protect the dust from reaching and depositing

onto the sensor (AMRI-3100). Normally optical sensors are

sensitive to light and its performance could be aﬀected if

its light receiving surface is covered with dust.

D. ESD Considerations

For electrostatic discharge, Wheel Deco that is mounted

onto the PCB could be coated with conductive plating

and grounded to system ground via ground pad on the

PCB. Additional grounding can be achieved through silver

net printing on metal dome sheet contact with the system

ground via Wheel Deco and mounting screws.

Figure 21. ESD Considerations and Implementation

Wheel / Dial

Sub Key

Wheel

Bottom

AMRI-3100

PCB/ FPC

Wheel Deco

Silver net printing on

top and grounded

Screw

Wheel

Bracket

Figure 22. Rotational Force and Frictions

E. Haptics Considerations

After all the mechanical parts are assembled together, it

is important to ensure the scrollwheel has good haptics

for example good rotation, clicks feel and etc. Therefore

during design stage, some of the following recommend-

ed considerations should be taken into account for good

haptics design.

I. Rotation (Grip vs. Internal Friction)

To enable rotation, the grip between ﬁnger and the

top surface of the wheel has to be greater than internal

friction of the scrollwheel. From Figure 22, friction at point

2 can be reduced by adding a UHMW sheet and a Teﬂon

based material for the bracket. Rotating Wheel must not

be rubbing against Wheel Deco and Center Button.

For better grip, following recommendations can be imple-

mented:

1. SF coating paint on Wheel or Dial (Example of paint

supplier, Ekzo Nobel)

2. Mechanical protruded rib

Do not use circular spin lines chrome ﬁnishing for the

surface of the Wheel due to poor grip. It tends to cause

ﬁnger to slip when rotating the Wheel.

Figure 23. Critical Gap Size for Smooth Rotation (mm)

Figure 22 illustrates on the recommended critical gap size

within the mechanical structures for smooth rotation.

Radial movement of the Wheel is controlled by Gap A.

Contact area should be minimized to reduce friction.

This is accomplished by designing the edge of the Wheel

Bracket slanted inward from the contact area instead of a

straight edge (refer to black dotted line at Gap A).

Besides adhering to the minimum size of the critical gaps,

there are other factors that are also important to provide

smooth rotation such as to ensure no rubbing of parts

against each other and having all possible sliding contact

surfaces polished to eliminate scratchy feel during

rotation. To ensure no rubbing between Wheel and Wheel

Bottom to the Center Button at location X and Wheel to

Wheel Bracket and Rubber Pad at location Y, gate cut has

to be controlled. The process of attaching the CW onto

the Wheel Bottom has to be properly controlled as well

because displacement of CW could potentially cause

friction when rubbing against its surrounding parts.

II. Wobbliness in Z-Direction

The wobbliness of the Wheel or Dial varies with the applied

force to rotate the Dial hence varying the torque created

to rotate it. When the Wheel wobbles, it will impact the

smoothness of rotation. Therefore it is recommended that

the Wheel Bracket is designed to hold on to the Wheel

ﬁrmly at the holding point that is further away from the

axis of rotation as illustrated in Figure 23. This feature of

the bracket will be able to consistently hold the Wheel

ﬁrmly and minimize wobbling during rotation.

Figure 24. Bracket Feature to Minimize Wobbling of Dial

Important Notes:

1. All tolerances of dimensions speciﬁed in the CW and all mechanical

parts has to be +0.05mm or better.

2. For more information on the AMRI-3100 sensor, kindly refer to the

datasheet of the sensor (AV02-1468EN)

For product information and a complete list of distributors, please go to our web site: www.avagotech.com

Avago, Avago Technologies, and the A logo are trademarks of Avago Technologies in the United States and other countries.

AV02-1491EN - September 10, 2008

Appendix A: Bill of Material (BOM) for Scrollwheel

Below is the BOM list for a scrollwheel.

No. Component Typical Part / Supplier Qty Comment

1 Wheel Deco

Plastic Housing Manufacturers

(Should be of Precision Plastic

Molders with capability up to

0.05mm tolerance)

1 Customized part from plastic parts supplier.

Material: PC or PC+ABS

2 Wheel/ Dial 1 Customized part from plastic parts supplier.

Material: PC or PC+ABS

3 Wheel Bracket 1 Customized part from plastic parts supplier.

Material: POM

4 Wheel Bottom 1 Customized part from plastic or metal stamping

parts supplier. Material: PC, PC+ABS or SUS 304.

5 Center Button 1 Customized part from plastic parts supplier.

Material: PC or PC+ABS

6 Codewheel Precision Silk Screen Printing

and Cutting Supplier

(Eg. C16S-A935-1 from

Nichibei Parts Sdn Bhd.)

1 Thickness is 0.23mm that is inclusive of stiﬀener

7 UHMW sheet

(optional)

Polymer Manufacturer

(Eg. 0470-000034 from

Chiyoda Integre Co.)

1 ID Ø14.4mm, OD Ø16.6mm, thickness 0.12mm.

For other dimension, please contact supplier.

Optional component, it provides smoother rotation.

8 Rubber Pad Precision Plastic

Manufacturers/Molders

1 Customized part from keypad supplier. Keypad

supplier will able to assemble item 1 to 8 to become

a sub-assembly.

9 PCB/ FPC 1 Customized part from PCB/FPC supplier.

i) AMRI-3100 Avago Technologies 1

ii) Metal Dome Switch 1 Customized part from metal dome sheet supplier.

iii) Chip LED 2 0603 SMT package; top ﬁring

iv) Resistor – 1kOhm 1 0201 SMT package; 1% tolerance; to be connected

to pin 5 (VC1) of AMRI-3100 (refer to datasheet)

v) Resistor – 10Ohm

(optional)

2 0201 SMT package; 10% tolerance; current limiting

resistor for Chip LED – only require if designed with

illumination

vi) Load Switch

(optional)

Eg. MIC94060 from Micrel For power down control

vii) Voltage level

translator switch

(optional)

Eg. ADG3242 from Analog

Devices

As level shifter to convert output signals of sensor

of 3.3V to 1.8V if necessary

The products of Avago Technologies are protected by various intellectual property rights in the

United States and in other countries in the world. Any use of such intellectual property rights with-

out the authorization of Avago Technologies is strictly prohibited and carries severe liabilities.

Broadcom AMRI-3100, Optical Sensor for Ultra-slim Scrollwheel User guide

Broadcom AMRI-3100, Optical Sensor for Ultra-slim Scrollwheel User guide

Broadcom AMRI-3100, Optical Sensor for Ultra-slim Scrollwheel User guide

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