LR Series Receiver Data Guide Datasheet by Linx Technologies Inc.

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Lir'i)'(' TECHNOLOGIES Wireless made simple®
LR Series
Receiver Module
Data Guide
!Table of Contents
1 Description
1 Features
1 Applications
2 Ordering Information
2 Absolute Maximum Ratings
3 Electrical Specifications
5 Typical Performance Graphs
7 Pin Assignments
7 Pin Descriptions
8 Module Description
9 Theory of Operation
10 Using the RSSI Pin
11 The Data Output
12 Using the PDN Line
13 Power Supply Requirements
13 ESD Concerns
14 Typical Applications
15 Transferring Data
16 Antenna Considerations
17 Helpful Application Notes from Linx
17 Protocol Guidelines
18 Interference Considerations
19 Pad Layout
19 Board Layout Guidelines
21 Microstrip Details
22 Production Guidelines
22 Hand Assembly
22 Automated Assembly
24 General Antenna Rules
Warning: Some customers may want Linx radio frequency (“RF”)
products to control machinery or devices remotely, including machinery
or devices that can cause death, bodily injuries, and/or property
damage if improperly or inadvertently triggered, particularly in industrial
settings or other applications implicating life-safety concerns (“Life and
Property Safety Situations”).
NO OEM LINX REMOTE CONTROL OR FUNCTION MODULE
SHOULD EVER BE USED IN LIFE AND PROPERTY SAFETY
SITUATIONS. No OEM Linx Remote Control or Function Module
should be modified for Life and Property Safety Situations. Such
modification cannot provide sufficient safety and will void the product’s
regulatory certification and warranty.
Customers may use our (non-Function) Modules, Antenna and
Connectors as part of other systems in Life Safety Situations, but
only with necessary and industry appropriate redundancies and
in compliance with applicable safety standards, including without
limitation, ANSI and NFPA standards. It is solely the responsibility
of any Linx customer who uses one or more of these products to
incorporate appropriate redundancies and safety standards for the Life
and Property Safety Situation application.
Do not use this or any Linx product to trigger an action directly
from the data line or RSSI lines without a protocol or encoder/
decoder to validate the data. Without validation, any signal from
another unrelated transmitter in the environment received by the module
could inadvertently trigger the action.
All RF products are susceptible to RF interference that can prevent
communication. RF products without frequency agility or hopping
implemented are more subject to interference. This module does not
have a frequency hopping protocol built in.
Do not use any Linx product over the limits in this data guide.
Excessive voltage or extended operation at the maximum voltage could
cause product failure. Exceeding the reflow temperature profile could
cause product failure which is not immediately evident.
Do not make any physical or electrical modifications to any Linx
product. This will void the warranty and regulatory and UL certifications
and may cause product failure which is not immediately evident.
!
Lir'ix TECHNOLOG‘ES
– –
1
Description
The LR Receiver is ideal for the wireless transfer
of serial data, control, or command information in
the favorable 260 to 470MHz band. The receiver’s
advanced synthesized architecture achieves an
outstanding typical sensitivity of –112dBm, which
provides a 5 to 10 times improvement in range over
previous solutions. When paired with a compatible
Linx transmitter, a reliable wireless link is formed
capable of transferring serial data at rates of up to 10,000bps at distances
of up to 1.5 miles (2,500m). This range may be reduced depending on the
regulations in the country of operation. Applications operating over shorter
distances or at lower data rates also benefit from increased link reliability
and superior noise immunity. Housed in a tiny reflow-compatible SMD
package, no external RF components are required (except an antenna),
allowing for easy integration, even for engineers without previous RF
experience.
Features
• Long range
• Low cost
• PLL-synthesized architecture
• Direct serial interface
• Data rates up to 10,000bps
• No external RF components
required
• Low power consumption
• Low supply voltage (2.1 to
3.6VDC)
• Compact surface-mount package
• Wide temperature range
• RSSI and Power-down function
• No production tuning
Applications
• Remote control
• Keyless entry
• Garage/gate openers
• Lighting control
• Medical monitoring/call systems
• Remote industrial monitoring
• Periodic data transfer
• Home/industrial automation
• Fire/security alarms
• Remote status/position sensing
• Long-range RFID
• Wire elimination
LR Series Receiver Module
Data Guide
Revised 3/18/2015
0.125 in
(3.12 mm)
0.630 in
(16mm)
0.812 in
(20.6mm)
LOT RRxxxx
RXM-315-LR
26 Common Antenna Styles
28 Regulatory Considerations
30 Notes
Figure 1: Package Dimensions
– – – –
2 3
LR Series Receiver Specifications
Parameter Symbol Min. Typ. Max. Units Notes
Power Supply
Operating Voltage VCC 2.7 3.0 3.6 VDC
With Dropping Resistor 4.3 5.0 5.2 VDC 1,5
Supply Current lCC 4.0 5.2 7.0 mA
Power Down Current lPDN 20.0 28.0 35.0 µA 5
Receiver Section
Receive Frequency Range FC
RXM-315-LR 315 MHz
RXM-418-LR 418 MHz
RXM-433-LR 433.92 MHz
Center Frequency Accuracy –50 +50 kHz
LO Feedthrough –80 dBm 2,5
IF Frequency FIF 10.7 MHz 5
Noise Bandwidth N3DB 280 kHz
Data Rate 100 10,000 bps
Data Output:
Logic Low VOL 0.0 VDC 3
Logic High VOH 3.0 VDC 3
Power Down Input:
Logic Low VIL 0.4 VDC
Logic High VIH VCC–0.4 VDC
Receiver Sensitivity –106 –112 –118 dBm 4
RSSI / Analog
Dynamic Range 80 dB 5
Analog Bandwidth 50 5,000 Hz 5
Gain 16 mv /
dB
5
Voltage with No Carrier 1.5 V 5
Antenna Port
RF Input Impedance RIN 50 Ω5
Timing
Receiver Turn-On Time
Via VCC 3.0 7.0 10.0 ms 5,6
Via PDN 0.04 0.25 0.50 nS 5,6
Electrical SpecificationsOrdering Information
Absolute Maximum Ratings
Ordering Information
Part Number Description
TXM-315-LR 315MHz Transmitter
TXM-418-LR 418MHz Transmitter
TXM-433-LR 433MHz Transmitter
RXM-315-LR 315MHz Receiver
RXM-418-LR 418MHz Receiver
RXM-433-LR 433MHz Receiver
EVAL-***-LR LR Series Basic Evaluation Kit
*** = 315, 418 (Standard), 433MHz
Receivers are supplied in tubes of 18 pcs.
Figure 2: Ordering Information
Absolute Maximum Ratings
Supply Voltage VCC −0.3 to +3.6 VDC
Supply Voltage VCC, Using Resistor −0.3 to +5.2 VDC
Any Input or Output Pin −0.3 to VCC + 0.3 VDC
RF Input 0 dBm
Operating Temperature −40 to +70 ºC
Storage Temperature −40 to +85 ºC
Soldering Temperature +260ºC for 10 seconds
Exceeding any of the limits of this section may lead to permanent damage to the device.
Furthermore, extended operation at these maximum ratings may reduce the life of this
device.
Figure 3: Absolute Maximum Ratings
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– – – –
4 5
LR Series Receiver Specifications Continued
Parameter Symbol Min. Typ. Max. Units Notes
Max. Time Between
Transitions
10.0 ms 5
Environmental
Operating Temperature
Range
–40 +70 ºC 5
1. The LR can utilize a 4.3 to 5.2VDC supply provided a 330Ω resistor is placed in series
with VCC.
2. Into a 50Ω load.
3. When operating from a 5V source, it is important to consider that the output will swing
to well less than 5 volts as a result of the required dropping resistor. Please verify that
the minimum voltage will meet the high threshold requirement of the device to which
data is being sent.
4. For BER of 10–5 at 1,200bps.
5. Characterized, but not tested.
6. Time to valid data output.
Warning: This product incorporates numerous static-sensitive
components. Always wear an ESD wrist strap and observe proper ESD
handling procedures when working with this device. Failure to observe
this precaution may result in module damage or failure.
Typical Performance Graphs
Supply
RX Data
RX Data
PDN
Figure 4: Electrical Specifications
Figure 5: Turn-On Time from VCC
Figure 6: Turn-On Time from PDN
1}“ J'L ' ‘ §mp M Pas: 0.000: CURSOR C 1 1D.flV CHZ‘SflflmV 10d)“
– – – –
6 7
Supply Current (mA)
Supply Voltage (VDC)
5.10
5.15
5.20
5.25
5.30
5.35
5.40
2.72.8 2.93.0 3.13.2 3.33.4 3.53.6 3.73.8 3.94.0 4.14.2 4.34.4 4.54.6 4.74.8 4.9 5.0 5.1 5.2
With Dropping
Resistor
RFIN > –35dBm
No RFIN
Figure 7: Consumption vs. Supply
Figure 8: RSSI Response Time
Pin Assignments
NC
NC
NC NC
NC
NC
NC
NC
NC
RSSI
GND
VCC
PDN
DATA
ANT
GND
1
2
3
4
5
6
7
89
10
11
12
13
14
15
16
Pin Descriptions
Figure 9: LR Series Receiver Pinout (Top View)
Figure 10: Pin Descriptions
Pin Descriptions
Pin Number Name I/O Description
1 NC No Connection
2 NC No Connection
3 NC No Connection
4 GND Analog Ground
5 VCC Supply Voltage
6 PDN I
Power Down. Pulling this line low will place
the receiver into a low-current state. The
module will not be able to receive a signal in
this state.
7 RSSI O
Received Signal Strength Indicator. This line
will supply an analog voltage that is propor-
tional to the strength of the received signal.
8DATA ODigital Data Output. This line will output the
demodulated digital data.
9 NC No Connection
10 NC No Connection
11 NC No Connection
12 NC No Connection
13 NC No Connection
14 NC No Connection
15 GND Analog Ground
16 RF IN 50Ω RF Input
8% Data Samar _m_
– – – –
8 9
Module Description
The LR receiver is a low-cost, high-performance synthesized AM / OOK
receiver, capable of receiving serial data at up to 10,000bps. Its exceptional
sensitivity results in outstanding range performance. The LR’s compact
surface-mount package is friendly to automated or hand production. LR
Series modules are capable of meeting the regulatory requirements of
many domestic and international applications.
The receiver's outstanding typical sensitivity of –112dBm enables system
ranges of up to 1.5 miles (2,500m) when paired with an LR Series
transmitter operating at full power and good antennas. Legal regulations
in the various countries will require the transmitter output power to be
reduced which will reduce range. Following the legal output limit for
transmitters in the United States, systems based on the LR Series can
achieve ranges of up to 3,000 feet (1,000m).
Data Slicer
LNA
VCOPLL
XTAL
90˚
Limiter
Data Out
RSSI/Analog
10.7MHz
IF Filter
Band Select
Filter
50 RF IN
(Antenna)
+
-
Figure 11: LR Series Receiver Block Diagram
Theory of Operation
The LR Series receiver is designed
to recover data sent by an AM
or Carrier-Present Carrier-Absent
(CPCA) transmitter, also referred to
as CW or On-Off Keying (OOK). This
type of modulation represents a logic
low '0’ by the absence of a carrier
and a logic high ‘1’ by the presence
of a carrier. This modulation method affords numerous benefits. The two
most important are: 1) cost-effectiveness due to design simplicity and 2)
higher allowable output power and thus greater range in countries (such as
the U.S.) that average output power measurements over time. Please refer
to Linx Application Note AN-00130 for a further discussion of modulation
techniques.
The LR receiver utilizes an advanced single-conversion superheterodyne
architecture. Transmitted signals enter the module through a 50Ω RF
port intended for single-ended connection to an external antenna. RF
signals entering the antenna are filtered and then amplified by an NMOS
cascode Low Noise Amplifier (LNA). The filtered, amplified signal is then
down-converted to a 10.7MHz Intermediate Frequency (IF) by mixing it
with a low-side Local Oscillator (LO). The LO frequency is generated by
a Voltage Controlled Oscillator (VCO) locked by a Phase-Locked Loop
(PLL) frequency synthesizer that utilizes a precision crystal reference. The
mixer stage incorporates a pair of double-balanced mixers and a unique
image rejection circuit. This circuit, along with the high IF frequency and
ceramic IF filters, reduces susceptibility to interference. The IF frequency is
further amplified, filtered, and demodulated to recover the baseband signal
originally transmitted. The baseband signal is squared by a data slicer and
output to the DATA pin. The architecture and quality of the components
utilized in the LR module enable it to outperform many far more expensive
receiver products.
Data
Carrier
Figure 12: CPCA (AM) Modulation
– – – –
10 11
Using the RSSI Pin
The receiver’s Received Signal Strength Indicator (RSSI) line outputs a
voltage that is proportional to the incoming signal strength. This line has
a dynamic range of 80dB (typical) and can serve a variety of functions. It
should be noted that the RSSI levels and dynamic range will vary slightly
from part to part. It is also important to remember that RSSI output
indicates the strength of any in-band RF energy and not necessarily just
that from the intended transmitter; therefore, it should be used only to
qualify the level and presence of a signal.
The RSSI output can be utilized during testing or even as a product feature
to assess interference and channel quality by looking at the RSSI level
with all intended transmitters shut off. The RSSI output can also be used
in direction-finding applications, although there are many potential perils to
consider in such systems. Finally, it can be used to save system power by
“waking up” external circuitry when a transmission is received or crosses a
certain threshold. The RSSI output feature adds tremendous versatility for
the creative designer.
The Data Output
The CMOS-compatible data output is normally used to drive a digital
decoder IC or a microprocessor that is performing the data decoding. It
does not have a large current drive capability so is intended to drive high
impedance loads, such as microprocessor inputs or digital logic gates.
The receiver’s output may appear to switch randomly in the absence of a
transmitter. This is a result of random noise in the environment. This noise
can be handled in software by implementing a noise-tolerant protocol
as described in Application Note AN-00160. If a software solution is not
appropriate, the squelch circuit in Figure 13 can be used. This circuit uses
a potentiometer to set a voltage reference. If the RSSI level falls below this
reference then a comparator turns off the DATA line and stops the random
switching.
This circuit is good for reducing the amount of random noise that the
microcontroller must deal with, but it also reduces the sensitivity of the
receiver since the received signal level must now be higher. This reduction
in sensitivity also reduces the system range. By using a potentiometer the
designer can make a compromise between noise level and range.
+
-
+
U1
LMV393
R4
100k
R1
2M
R2
500k
C1
0.1µ
D1
RSSI
DATA
Squelched Data
VCC
R3
5M
VCC
+
-
U1
LMV393
VCC
R5
1M
R6
1M
R7
2M
R8
10k
1
2
3
5
6
7
Figure 13: LR Series Receiver Squelch Circuit
p IIH
– – – –
12 13
Power Supply Requirements
The module does not have an internal
voltage regulator, therefore it requires a
clean, well-regulated power source. While
it is preferable to power the unit from a
battery, it can also be operated from a
power supply as long as noise is less than
20mV. Power supply noise can significantly
affect the receiver sensitivity, therefore;
providing clean power to the module should
be a high priority during design.
A 10Ω resistor in series with the supply followed by a 10µF tantalum
capacitor from VCC to ground will help in cases where the quality of the
supply power is poor. These values may need to be adjusted depending on
the noise present on the supply line.
The module can be operated from 4.3V to 5.2V by using an external 330Ω
series resistor to prevent VCC from exceeding 3.6V. This resistor can replace
the 10Ω in the supply filter. While the receiver's current consumption is
constant and makes this possible, it is recommended to operate the
receiver from a 3.0 to 3.3V supply
ESD Concerns
The module has basic ESD protection built in, but in cases where the
antenna connection is exposed to the user it is a good idea to add
additional protection. A Transient Voltage Suppressor (TVS) diode, varistor
or similar component can be added to the antenna line. These should have
low capacitance and be designed for use on antennas. Protection on the
supply line is a good idea in designs that have a user-accessible power
port.
Figure 14: Supply Filter
+
10
10µF
Vcc IN
Vcc TO
MODULE
Using the PDN Line
The Power Down (PDN) line can be used to power down the receiver
without the need for an external switch. This line has an internal pull-up, so
when it is held high or simply left floating, the module is active.
When the PDN line is pulled to ground, the receiver enters a low-current
(<40µA) power-down mode. During this time the receiver is off and cannot
perform any function. It may be useful to note that the startup time coming
out of power-down is slightly less than when applying VCC.
The PDN line allows easy control of the receiver state from external
components, like a microcontroller. By periodically activating the receiver,
checking for data, then powering down, the receiver’s average current
consumption can be greatly reduced, saving power in battery-operated
applications.
Note: The voltage on the PDN line should not exceed VCC. When used
with a higher voltage source, such as a 5V microcontroller, an open
collector line should be used or a diode placed in series with the control
line (anode toward the module). Either method avoids damage to the
module by preventing 5V from being placed on the PDN line while
allowing the line to be pulled low.
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– – – –
14 15
Typical Applications
Figure 15 shows a circuit using the Linx LICAL-DEC-MS001 decoder.
This chip works with the LICAL-ENC-MS001 encoder to provide simple
remote control capabilities. The decoder detects the transmission from
the encoder, checks for errors, and if everything is correct, replicates the
encoder’s inputs on its outputs. This makes sending key presses very easy.
More information on the operation and features of the decoder can be
found in the MS Series Decoder Data Guide.
The receiver can also be connected to a GPIO of a microcontroller in
applications that use a custom protocol. No buffering is generally required
to drive a microcontroller input. Exceptions to this include systems where
the microcontroller is operating at a different voltage from the receiver. In
these cases the designer should take care to use voltage translator circuits
as appropriate.
N
N
V
CC
N
C
1
N
C
2
N
C
3
N
4
V
CC
5
PDN
6
R
SSI
7
DATA
8
N
C
9
N
C
1
0
N
C
11
N
C
12
N
C
1
3
N
C
1
4
G
N
D
1
5
ANT
1
6
RXM
-
LR
22
0
1
00k
D
6
D7
SEL
_
BAUD
0
SEL
_
BAUD
1
N
N
LAT
CH
RX
_
CNT
L
TX
_
I
D
MODE
_
IN
D
D
5
D4
D
3
D2
V
CC
V
CC
D1
D
0
DATA
_
I
N
LEARN
1
2
3
4
5
6
7
8
9
1
0
1
1
12
1
3
14
15
1
6
17
1
8
1
9
2
0
LI
C
AL-DE
C
-M
S001
V
CC
N
N
V
CC
2.2k
1
0k
V
CC
RELAY
S
WIT
C
HED
OU
TP
UT
Figure 15: LR Series Receiver and MS Series Decoder
Transferring Data
Once a reliable RF link has been established, the challenge becomes how
to effectively transfer data across it. While a properly designed RF link
provides reliable data transfer under most conditions, there are still distinct
differences from a wired link that must be addressed. Since the LR Series
modules do not incorporate internal encoding or decoding, a user has
tremendous flexibility in how data is handled.
If the product transfers simple control or status signals such as button
presses or switch closures and it does not have a microprocessor on board
(or it is desired to avoid protocol development), consider using a remote
control encoder and decoder or a transcoder IC. These chips are available
from a wide range of manufacturers including Linx. They take care of all
encoding and decoding functions, and generally provide a number of data
pins to which switches can be directly connected. In addition, address bits
are usually provided for security and to allow the addressing of multiple
units independently. These ICs are an excellent way to bring basic remote
control / status products to market quickly and inexpensively. Additionally,
it is a simple task to interface with inexpensive microprocessors, IR, remote
control or modem ICs.
It is always important to separate the types of transmissions that are
technically possible from those that are legally allowable in the country
of intended operation. Linx Application Notes AN-00125, AN-00128
and AN-00140 should be reviewed, along with Part 15, Section 231 of
the Code of Federal Regulations for further details regarding acceptable
transmission content in the US All of these documents can be downloaded
from the Linx website at www.linxtechnologies.com.
Another area of consideration is that the data structure can affect the
output power level. The FCC allows output power in the 260 to 470MHz
band to be averaged over a 100ms time frame. Because OOK modulation
activates the carrier for a ‘1’ and deactivates the carrier for a ‘0’, a data
stream that sends more ‘0’s has a lower average output power over
100ms. This allows the instantaneous output power to be increased, thus
extending range.
Tum ‘Qiéun
– – – –
16 17
Antenna Considerations
The choice of antennas is a
critical and often overlooked
design consideration. The range,
performance and legality of an RF
link are critically dependent upon the
antenna. While adequate antenna
performance can often be obtained
by trial and error methods, antenna
design and matching is a complex
task. Professionally designed antennas such as those from Linx (Figure
16) help ensure maximum performance and FCC and other regulatory
compliance.
Linx transmitter modules typically have an output power that is higher
than the legal limits. This allows the designer to use an inefficient antenna
such as a loop trace or helical to meet size, cost or cosmetic requirements
and still achieve full legal output power for maximum range. If an efficient
antenna is used, then some attenuation of the output power will likely be
needed. This can easily be accomplished by using the LADJ line.
A receiver antenna should be optimized for the frequency or band in
which the receiver operates and to minimize the reception of off-frequency
signals. The efficiency of the receiver’s antenna is critical to maximizing
range performance. Unlike the transmitter antenna, where legal operation
may mandate attenuation or a reduction in antenna efficiency, the receiver’s
antenna should be optimized as much as is practical.
It is usually best to utilize a basic quarter-wave whip until your prototype
product is operating satisfactorily. Other antennas can then be evaluated
based on the cost, size and cosmetic requirements of the product.
Additional details are in Application Note AN-00500.
Figure 16: Linx Antennas
Helpful Application Notes from Linx
It is not the intention of this manual to address in depth many of the issues
that should be considered to ensure that the modules function correctly
and deliver the maximum possible performance. We recommend reading
the application notes listed in Figure 17 which address in depth key areas
of RF design and application of Linx products. These applications notes are
available online at www.linxtechnologies.com or by contacting Linx.
Protocol Guidelines
While many RF solutions impose data formatting and balancing
requirements, Linx RF modules do not encode or packetize the signal
content in any manner. The received signal will be affected by such factors
as noise, edge jitter and interference, but it is not purposefully manipulated
or altered by the modules. This gives the designer tremendous flexibility for
protocol design and interface.
Despite this transparency and ease of use, it must be recognized that there
are distinct differences between a wired and a wireless environment. Issues
such as interference and contention must be understood and allowed for in
the design process. To learn more about protocol considerations, read Linx
Application Note AN-00160.
Interference or changing signal conditions can corrupt the data packet,
so it is generally wise to structure the data being sent into small packets.
This allows errors to be managed without affecting large amounts of data.
A simple checksum or CRC could be used for basic error detection. Once
an error is detected, the protocol designer may wish to simply discard the
corrupt data or implement a more sophisticated scheme to correct it.
Helpful Application Note Titles
Note Number Note Title
AN-00100 RF 101: Information for the RF Challenged
AN-00125 Considerations for Operation Within the 260–470MHz Band
AN-00130 Modulation Techniques for Low-Cost RF Data Links
AN-00140 The FCC Road: Part 15 from Concept to Approval
AN-00150 Use and Design of T-Attenuation Pads
AN-00160 Considerations for Sending Data over a Wireless Link
AN-00232 General Considerations for Sending Data with the LC Series
AN-00500 Antennas: Design, Application, Performance
AN-00501 Understanding Antenna Specifications and Operation
Figure 17: Helpful Application Note Titles
—>| I‘—
– – – –
18 19
Interference Considerations
The RF spectrum is crowded and the potential for conflict with unwanted
sources of RF is very real. While all RF products are at risk from
interference, its effects can be minimized by better understanding its
characteristics.
Interference may come from internal or external sources. The first step
is to eliminate interference from noise sources on the board. This means
paying careful attention to layout, grounding, filtering and bypassing in
order to eliminate all radiated and conducted interference paths. For
many products, this is straightforward; however, products containing
components such as switching power supplies, motors, crystals and other
potential sources of noise must be approached with care. Comparing your
own design with a Linx evaluation board can help to determine if and at
what level design-specific interference is present.
External interference can manifest itself in a variety of ways. Low-level
interference produces noise and hashing on the output and reduces the
link’s overall range.
High-level interference is caused by nearby products sharing the same
frequency or from near-band high-power devices. It can even come from
your own products if more than one transmitter is active in the same area.
It is important to remember that only one transmitter at a time can occupy
a frequency, regardless of the coding of the transmitted signal. This type of
interference is less common than those mentioned previously, but in severe
cases it can prevent all useful function of the affected device.
Although technically not interference, multipath is also a factor to be
understood. Multipath is a term used to refer to the signal cancellation
effects that occur when RF waves arrive at the receiver in different phase
relationships. This effect is a particularly significant factor in interior
environments where objects provide many different signal reflection paths.
Multipath cancellation results in lowered signal levels at the receiver and
shorter useful distances for the link.
Pad Layout
The pad layout diagram in Figure 18 is designed to facilitate both hand and
automated assembly.
Board Layout Guidelines
The module’s design makes integration straightforward; however, it
is still critical to exercise care in PCB layout. Failure to observe good
layout techniques can result in a significant degradation of the module’s
performance. A primary layout goal is to maintain a characteristic
50-ohm impedance throughout the path from the antenna to the module.
Grounding, filtering, decoupling, routing and PCB stack-up are also
important considerations for any RF design. The following section provides
some basic design guidelines.
During prototyping, the module should be soldered to a properly laid-out
circuit board. The use of prototyping or “perf” boards results in poor
performance and is strongly discouraged. Likewise, the use of sockets
can have a negative impact on the performance of the module and is
discouraged.
The module should, as much as reasonably possible, be isolated from
other components on your PCB, especially high-frequency circuitry such as
crystal oscillators, switching power supplies, and high-speed bus lines.
When possible, separate RF and digital circuits into different PCB regions.
Figure 18: Recommended PCB Layout
0.100"
0.070"
0.065"
0.610"
+i w 44 mm W m i 2 1 — F , , d (L+ I wuusm- “(L +| 440) d .1 : Dmlecmc comlzm M Van mammal
– – – –
20 21
Microstrip Details
A transmission line is a medium whereby RF energy is transferred from
one place to another with minimal loss. This is a critical factor, especially
in high-frequency products like Linx RF modules, because the trace
leading to the module’s antenna can effectively contribute to the length
of the antenna, changing its resonant bandwidth. In order to minimize
loss and detuning, some form of transmission line between the antenna
and the module should be used unless the antenna can be placed very
close (<1/8in) to the module. One common form of transmission line is a
coax cable and another is the microstrip. This term refers to a PCB trace
running over a ground plane that is designed to serve as a transmission line
between the module and the antenna. The width is based on the desired
characteristic impedance of the line, the thickness of the PCB and the
dielectric constant of the board material. For standard 0.062in thick FR-4
board material, the trace width would be 111 mils. The correct trace width
can be calculated for other widths and materials using the information in
Figure 19 and examples are provided in Figure 20. Software for calculating
microstrip lines is also available on the Linx website.
Trace
Board
Ground plane
Figure 19: Microstrip Formulas
Example Microstrip Calculations
Dielectric Constant Width / Height
Ratio (W / d)
Effective Dielectric
Constant
Characteristic
Impedance (Ω)
4.80 1.8 3.59 50.0
4.00 2.0 3.07 51.0
2.55 3.0 2.12 48.8
Figure 20: Example Microstrip Calculations
Make sure internal wiring is routed away from the module and antenna and
is secured to prevent displacement.
Do not route PCB traces directly under the module. There should not be
any copper or traces under the module on the same layer as the module,
just bare PCB. The underside of the module has traces and vias that could
short or couple to traces on the product’s circuit board.
The Pad Layout section shows a typical PCB footprint for the module. A
ground plane (as large and uninterrupted as possible) should be placed on
a lower layer of your PC board opposite the module. This plane is essential
for creating a low impedance return for ground and consistent stripline
performance.
Use care in routing the RF trace between the module and the antenna
or connector. Keep the trace as short as possible. Do not pass it under
the module or any other component. Do not route the antenna trace on
multiple PCB layers as vias add inductance. Vias are acceptable for tying
together ground layers and component grounds and should be used in
multiples.
Each of the module’s ground pins should have short traces tying
immediately to the ground plane through a via.
Bypass caps should be low ESR ceramic types and located directly
adjacent to the pin they are serving.
A 50-ohm coax should be used for connection to an external antenna.
A 50-ohm transmission line, such as a microstrip, stripline or coplanar
waveguide should be used for routing RF on the PCB. The Microstrip
Details section provides additional information.
In some instances, a designer may wish to encapsulate or “pot” the
product. There are a wide variety of potting compounds with varying
dielectric properties. Since such compounds can considerably impact
RF performance and the ability to rework or service the product, it is
the responsibility of the designer to evaluate and qualify the impact and
suitability of such materials.
– – – –
22 23
Production Guidelines
The module is housed in a hybrid SMD package that supports hand and
automated assembly techniques. Since the modules contain discrete
components internally, the assembly procedures are critical to ensuring
the reliable function of the modules. The following procedures should be
reviewed with and practiced by all assembly personnel.
Hand Assembly
Pads located on the bottom
of the module are the primary
mounting surface (Figure 21).
Since these pads are inaccessible
during mounting, castellations
that run up the side of the module
have been provided to facilitate
solder wicking to the module’s
underside. This allows for very
quick hand soldering for prototyping and small volume production. If the
recommended pad guidelines have been followed, the pads will protrude
slightly past the edge of the module. Use a fine soldering tip to heat the
board pad and the castellation, then introduce solder to the pad at the
module’s edge. The solder will wick underneath the module, providing
reliable attachment. Tack one module corner first and then work around the
device, taking care not to exceed the times in Figure 22.
Automated Assembly
For high-volume assembly, the modules are generally auto-placed.
The modules have been designed to maintain compatibility with reflow
processing techniques; however, due to their hybrid nature, certain aspects
of the assembly process are far more critical than for other component
types. Following are brief discussions of the three primary areas where
caution must be observed.
Castellations
PCB Pads
Soldering Iron
Tip
Solder
Figure 21: Soldering Technique
Warning: Pay attention to the absolute maximum solder times.
Figure 22: Absolute Maximum Solder Times
Absolute Maximum Solder Times
Hand Solder Temperature: +427ºC for 10 seconds for lead-free alloys
Reflow Oven: +255ºC max (see Figure 23)
Reflow Temperature Profile
The single most critical stage in the automated assembly process is the
reflow stage. The reflow profile in Figure 23 should not be exceeded
because excessive temperatures or transport times during reflow will
irreparably damage the modules. Assembly personnel need to pay careful
attention to the oven’s profile to ensure that it meets the requirements
necessary to successfully reflow all components while still remaining
within the limits mandated by the modules. The figure below shows the
recommended reflow oven profile for the modules.
Shock During Reflow Transport
Since some internal module components may reflow along with the
components placed on the board being assembled, it is imperative that
the modules not be subjected to shock or vibration during the time solder
is liquid. Should a shock be applied, some internal components could be
lifted from their pads, causing the module to not function properly.
Washability
The modules are wash-resistant, but are not hermetically sealed. Linx
recommends wash-free manufacturing; however, the modules can be
subjected to a wash cycle provided that a drying time is allowed prior
to applying electrical power to the modules. The drying time should be
sufficient to allow any moisture that may have migrated into the module
to evaporate, thus eliminating the potential for shorting damage during
power-up or testing. If the wash contains contaminants, the performance
may be adversely affected, even after drying.
125°C
185°C
217°C
255°C
235°C
60 12030 150180 210240 270300 330360090
50
100
150
200
250
300
Recommended RoHS Profile
Max RoHS Profile
Recommended Non-RoHS Profile
180°C
Temperature (oC)
Time (Seconds)
Figure 23: Maximum Reflow Temperature Profile
– – – –
24 25
General Antenna Rules
The following general rules should help in maximizing antenna performance.
1. Proximity to objects such as a user’s hand, body or metal objects will
cause an antenna to detune. For this reason, the antenna shaft and tip
should be positioned as far away from such objects as possible.
2. Optimum performance is obtained from a ¼- or ½-wave straight whip
mounted at a right angle to the ground plane (Figure 24). In many
cases, this isn’t desirable for practical or ergonomic reasons, thus,
an alternative antenna style such as a helical, loop or patch may be
utilized and the corresponding sacrifice in performance accepted.
3. If an internal antenna is to be used, keep it away from other metal
components, particularly large items like transformers, batteries,
PCB tracks and ground planes. In many cases, the space around the
antenna is as important as the antenna itself. Objects in close proximity
to the antenna can cause direct detuning, while those farther away will
alter the antenna’s symmetry.
4. In many antenna designs, particularly ¼-wave whips, the ground plane
acts as a counterpoise, forming, in essence,
a ½-wave dipole (Figure 25). For this reason,
adequate ground plane area is essential.
The ground plane can be a metal case or
ground-fill areas on a circuit board. Ideally, it
should have a surface area less than or equal
to the overall length of the ¼-wave radiating
element. This is often not practical due to
size and configuration constraints. In these
instances, a designer must make the best use
of the area available to create as much ground
OPTIMUM
USABLE NOT RECOMMENDED
NUT GROUND PLANE
(MAY BE NEEDED)
CASE
Figure 24: Ground Plane Orientation
I
EDIPOLE
ELEMENT
GROUND
PLANE
VIRTUAL λ/4
DIPOLE
λ/4
λ/4
VERTICAL λ/4 GROUNDED
ANTENNA (MARCONI)
plane as possible in proximity to the base of the antenna. In cases
where the antenna is remotely located or the antenna is not in close
proximity to a circuit board, ground plane or grounded metal case, a
metal plate may be used to maximize the antenna’s performance.
5. Remove the antenna as far as possible from potential interference
sources. Any frequency of sufficient amplitude to enter the receiver’s
front end will reduce system range and can even prevent reception
entirely. Switching power supplies, oscillators or even relays can also
be significant sources of potential interference. The single best weapon
against such problems is attention to placement and layout. Filter the
module’s power supply with a high-frequency bypass capacitor. Place
adequate ground plane under potential sources of noise to shunt noise
to ground and prevent it from coupling to the RF stage. Shield noisy
board areas whenever practical.
6. In some applications, it is advantageous to place the module and
antenna away from the main equipment (Figure 26). This can avoid
interference problems and allows the antenna to be oriented for
optimum performance. Always use 50Ω coax, like RG-174, for the
remote feed.
OPTIMUM
USABLE NOT RECOMMENDED
NUT GROUND PLANE
(MAY BE NEEDED)
CASE
Figure 26: Remote Ground Plane
Figure 25: Dipole Antenna
– – – –
26 27
Common Antenna Styles
There are hundreds of antenna styles and variations that can be employed
with Linx RF modules. Following is a brief discussion of the styles most
commonly utilized. Additional antenna information can be found in Linx
Application Notes AN-00100, AN-00140, AN-00500 and AN-00501. Linx
antennas and connectors offer outstanding performance at a low price.
Whip Style
A whip style antenna (Figure 27) provides
outstanding overall performance and stability.
A low-cost whip can be easily fabricated from
a wire or rod, but most designers opt for the
consistent performance and cosmetic appeal of
a professionally-made model. To meet this need,
Linx offers a wide variety of straight and reduced
height whip style antennas in permanent and
connectorized mounting styles.
The wavelength of the operational frequency
determines an antenna’s overall length. Since a full
wavelength is often quite long, a partial ½- or ¼-wave
antenna is normally employed. Its size and natural
radiation resistance make it well matched to Linx
modules. The proper length for a straight ¼-wave can
be easily determined using the formula in Figure 28. It is
also possible to reduce the overall height of the antenna
by using a helical winding. This reduces the antenna’s bandwidth but is a
great way to minimize the antenna’s physical size for compact applications.
This also means that the physical appearance is not always an indicator of
the antenna’s frequency.
Specialty Styles
Linx offers a wide variety of specialized antenna
styles (Figure 29). Many of these styles utilize helical
elements to reduce the overall antenna size while
maintaining reasonable performance. A helical
antenna’s bandwidth is often quite narrow and the
antenna can detune in proximity to other objects, so
care must be exercised in layout and placement.
L =
234
F
MHz
Figure 27: Whip Style Antennas
Figure 28:
L = length in feet of
quarter-wave length
F = operating frequency
in megahertz
Figure 29: Specialty Style
Antennas
Loop Style
A loop or trace style antenna is normally printed
directly on a product’s PCB (Figure 30). This
makes it the most cost-effective of antenna
styles. The element can be made self-resonant or
externally resonated with discrete components,
but its actual layout is usually product specific.
Despite the cost advantages, loop style antennas
are generally inefficient and useful only for short
range applications. They are also very sensitive to changes in layout and
PCB dielectric, which can cause consistency issues during production.
In addition, printed styles are difficult to engineer, requiring the use of
expensive equipment including a network analyzer. An improperly designed
loop will have a high VSWR at the desired frequency which can cause
instability in the RF stage.
Linx offers low-cost planar (Figure 31) and chip
antennas that mount directly to a product’s PCB.
These tiny antennas do not require testing and
provide excellent performance despite their small
size. They offer a preferable alternative to the often
problematic “printed” antenna.
Figure 30: Loop or Trace Antenna
Figure 31: SP Series
“Splatch” and uSP
“MicroSplatch” Antennas
– – – –
28 29
Regulatory Considerations
When working with RF, a clear distinction must be made between what
is technically possible and what is legally acceptable in the country where
operation is intended. Many manufacturers have avoided incorporating RF
into their products as a result of uncertainty and even fear of the approval
and certification process. Here at Linx, our desire is not only to expedite the
design process, but also to assist you in achieving a clear idea of what is
involved in obtaining the necessary approvals to legally market a completed
product.
For information about regulatory approval, read AN-00142 on the Linx
website or call Linx. Linx designs products with worldwide regulatory
approval in mind.
In the United States, the approval process is actually quite straightforward.
The regulations governing RF devices and the enforcement of them are
the responsibility of the Federal Communications Commission (FCC). The
regulations are contained in Title 47 of the United States Code of Federal
Regulations (CFR). Title 47 is made up of numerous volumes; however,
all regulations applicable to this module are contained in Volume 0-19.
It is strongly recommended that a copy be obtained from the FCC’s
website, the Government Printing Office in Washington or from your local
government bookstore. Excerpts of applicable sections are included
with Linx evaluation kits or may be obtained from the Linx Technologies
website, www.linxtechnologies.com. In brief, these rules require that any
device that intentionally radiates RF energy be approved, that is, tested for
compliance and issued a unique identification number. This is a relatively
painless process. Final compliance testing is performed by one of the many
independent testing laboratories across the country. Many labs can also
provide other certifications that the product may require at the same time,
such as UL, CLASS A / B, etc. Once the completed product has passed,
an ID number is issued that is to be clearly placed on each product
manufactured.
Note: Linx RF modules are designed as component devices that require
external components to function. The purchaser understands that
additional approvals may be required prior to the sale or operation of
the device, and agrees to utilize the component in keeping with all laws
governing its use in the country of operation.
Questions regarding interpretations of the Part 2 and Part 15 rules or the
measurement procedures used to test intentional radiators such as Linx RF
modules for compliance with the technical standards of Part 15 should be
addressed to:
Federal Communications Commission
Equipment Authorization Division
Customer Service Branch, MS 1300F2
7435 Oakland Mills Road
Columbia, MD, US 21046
Phone: + 1 301 725 585 | Fax: + 1 301 344 2050
Email: labinfo@fcc.gov
ETSI Secretaria
650, Route des Lucioles
06921 Sophia-Antipolis Cedex
FRANCE
Phone: +33 (0)4 92 94 42 00
Fax: +33 (0)4 93 65 47 16
International approvals are slightly more complex, although Linx modules
are designed to allow all international standards to be met. If the end
product is to be exported to other countries, contact Linx to determine the
specific suitability of the module to the application.
All Linx modules are designed with the approval process in mind and thus
much of the frustration that is typically experienced with a discrete design is
eliminated. Approval is still dependent on many factors, such as the choice
of antennas, correct use of the frequency selected and physical packaging.
While some extra cost and design effort are required to address these
issues, the additional usefulness and profitability added to a product by RF
makes the effort more than worthwhile.
– – – –
30 31
Notes
Lir'ix TECHNOLOGIES
Disclaimer
Linx Technologies is continually striving to improve the quality and function of its products. For this reason, we
reserve the right to make changes to our products without notice. The information contained in this Data Guide
is believed to be accurate as of the time of publication. Specifications are based on representative lot samples.
Values may vary from lot-to-lot and are not guaranteed. “Typical” parameters can and do vary over lots and
application. Linx Technologies makes no guarantee, warranty, or representation regarding the suitability of any
product for use in any specific application. It is the customer’s responsibility to verify the suitability of the part for
the intended application. NO LINX PRODUCT IS INTENDED FOR USE IN ANY APPLICATION WHERE THE SAFETY
OF LIFE OR PROPERTY IS AT RISK.
Linx Technologies DISCLAIMS ALL WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
PURPOSE. IN NO EVENT SHALL LINX TECHNOLOGIES BE LIABLE FOR ANY OF CUSTOMER’S INCIDENTAL OR
CONSEQUENTIAL DAMAGES ARISING IN ANY WAY FROM ANY DEFECTIVE OR NON-CONFORMING PRODUCTS
OR FOR ANY OTHER BREACH OF CONTRACT BY LINX TECHNOLOGIES. The limitations on Linx Technologies’
liability are applicable to any and all claims or theories of recovery asserted by Customer, including, without
limitation, breach of contract, breach of warranty, strict liability, or negligence. Customer assumes all liability
(including, without limitation, liability for injury to person or property, economic loss, or business interruption) for
all claims, including claims from third parties, arising from the use of the Products. The Customer will indemnify,
defend, protect, and hold harmless Linx Technologies and its officers, employees, subsidiaries, affiliates,
distributors, and representatives from and against all claims, damages, actions, suits, proceedings, demands,
assessments, adjustments, costs, and expenses incurred by Linx Technologies as a result of or arising from any
Products sold by Linx Technologies to Customer. Under no conditions will Linx Technologies be responsible for
losses arising from the use or failure of the device in any application, other than the repair, replacement, or refund
limited to the original product purchase price. Devices described in this publication may contain proprietary,
patented, or copyrighted techniques, components, or materials. Under no circumstances shall any user be
conveyed any license or right to the use or ownership of such items.
©2015 Linx Technologies. All rights reserved.
The stylized Linx logo, Wireless Made Simple, WiSE, CipherLinx and the stylized CL logo are trademarks of Linx Technologies.
Linx Technologies
159 Ort Lane
Merlin, OR, US 97532
Phone: +1 541 471 6256
Fax: +1 541 471 6251
www.linxtechnologies.com

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