TXM-315-LC
TXM-418-LC
TXM-433-LC
WIRELESS MADE SIMPLE
®
LC SERIES TRANSMITTER MODULE DATA GUIDE
DESCRIPTION
The LC Series is ideally suited for volume use in
OEM applications such as remote control,
security, identification, and periodic data
transfer. Housed in a compact surface-mount
package, the LC Series transmitter utilizes a
highly-optimized SAW architecture to achieve
an unmatched blend of performance, size,
efficiency, and cost. When paired with a
matching LC Series or LR Series receiver, a
highly reliable wireless link is formed, capable
of transferring serial data at distances in excess
of 300 feet (LC) or up to 3,000 feet (LR). No
external RF components are required (except
an antenna), making design and integration
straightforward, even for engineers without
previous RF experience.
0.360"
TXM-418-LC
LOT 2000
RF MODULE
0.500"
0.150"
Max.
Figure 1: Package Dimensions
FEATURES
Low cost
No external RF components
required
Ultra-low power consumption
Compact surface-mount package
Stable SAW-based architecture
Supports data rates to 5,000bps
Wide supply range
(2.7 to 5.2VDC)
Direct serial interface
Low harmonics
No production tuning
APPLICATIONS INCLUDE
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 Sensing
Long-Range RFID
Wire Elimination
ORDERING INFORMATION
PART #
DESCRIPTION
TXM-315-LC
Transmitter 315MHz
TXM-418-LC
Transmitter 418MHz
TXM-433-LC
Transmitter 433MHz
RXM-315-LC
Receiver 315MHz
RXM-418-LC
Receiver 418MHz
RXM-433-LC
Receiver 433MHz
EVAL-***-LC
Basic Evaluation Kit
*** = Frequency
Transmitters are supplied in tubes of 50 pcs.
Revised 1/28/08
ELECTRICAL SPECIFICATIONS
Parameter
POWER SUPPLY
Operating Voltage
Supply Current
Power-down Current
TRANSMITTER SECTION
Transmit Frequency:
TXM-315-LC
TXM-418-LC
TXM-433-LC
Center Frequency Accuracy
Output Power
Harmonic Emissions
Data Rate
Data Input:
Logic Low
Logic High
ANTENNA PORT
RF Output Impedance
TIMING
Transmitter Turn-On Time
Transmitter Turn-Off Time
ENVIRONMENTAL
Operating Temperature Range
–
-30
–
+70
–
–
–
100
–
–
30
80
µSec
nSec
5
5
R
OUT
–
50
–
Ω
5
V
IH
2.5
–
Vcc
VDC
V
IL
0.0
–
0.4
VDC
–
–
–
100
–
5,000
bps
–
Supply Current (mA)
PERFORMANCE DATA
Typical
Max.
Units
Notes
Designation
Min.
V
CC
I
CC
I
PDN
F
C
–
–
–
–
P
o
P
H
–
–
-40
dBc
3
-4
0
+4
dBm
3
-50
–
+50
kHz
–
433.92
–
MHz
–
418
–
MHz
–
315
–
MHz
–
–
–
1.5
µA
2
–
3.0
6.0
mA
1,4
2.7
–
5.2
VDC
–
These performance parameters
are based on module operation at
25°C from a 3.3VDC supply unless
otherwise
noted.
Figure
2
illustrates
the
connections
necessary
for
testing
and
operation. It is recommended all
ground pins be connected to the
ground plane.
VCC
1
2
3
4
GND
GND
DATA
VCC
GND
GND
LADJ/GND ANT
8
7
6
5
Figure 2: Test / Basic Application Circuit
TYPICAL PERFORMANCE GRAPHS
12
11
10
9
8
7
6
5
4
3
2
1
0
2.5
+8
+7
+6
+5
+4
+3
+2
+1
0
-1
-2
-3
-4
-5
°
C
5
3.0
3.5
4.0
4.5
Supply Voltage (V)
5.0
Output Power (dBm)
2.5
3.0
3.5 4.0 4.5
Supply Voltage (V)
5.0
Table 1: LC Series Transmitter Specifications
With LADJ tied to ground
With 430Ω resistor on LADJ
With LADJ tied to ground
With 430Ω resistor on LADJ
Notes
1.
2.
3.
4.
5.
Current draw with DATA pin held continuously high.
Current draw with DATA pin low.
RF out connected to a 50Ω load.
LADJ through 430Ω resistor.
Characterized, but not tested.
Figure 3: Current vs. Supply Voltage
Figure 4: Output Power vs. Supply Voltage
Data
Data
ABSOLUTE MAXIMUM RATINGS
Supply Voltage V
CC
Any Input or Output Pin
Operating Temperature
Storage Temperature
Soldering Temperature
-0.3
-0.3
-30
-45
+225°C
to
+6.0
to
V
CC
to
+70
to
+85
for 10 seconds
VDC
VDC
°C
°C
Carrier
Carrier
Figure 5: Typical Oscillator Turn-On Time
+8
+7
+6
+5
+4
+3
+2
+1
0
-1
-2
-3
-4
Figure 6: Typical Oscillator Turn-Off Time
Output Power (dBm)
*NOTE*
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.
5V
*CAUTION*
3V
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.
Page 2
51 100 150 200 240 300 360 430 510 560 620 680 750 820
910
1.1K
LADJ Resistor Value (Ω)
Figure 7: Output Power vs. LADJ Resistor
Page 3
PIN ASSIGNMENTS
MODULE DESCRIPTION
1
2
3
4
8
7
6
5
50Ω RF OUT
(ANT)
GND
GND
DATA
VCC
GND
GND
LADJ/GND ANT
The LC Series transmitter is a low-cost, high-performance Surface Acoustic
Wave (SAW) based Carrier-Present Carrier-Absent (CPCA) transmitter capable
of sending serial data at up to 5,000bps. The LC’s compact surface-mount
package integrates easily into existing designs and is equally friendly to
prototype and volume production. The LC’s ultra-low power consumption makes
it ideally suited for battery-powered products. When combined with a Linx LC or
LR Series receiver, a reliable RF link is formed, capable of transferring data over
line-of-sight distances in excess of 300 feet (with the LC Series receiver) or up
to 3,000 feet (with the LR Series receiver).
Figure 8: LC Series Transmitter Pinout (Top View)
SAW
Oscillator
Vcc
PIN DESCRIPTIONS
Pin #
1
2
3
GND
Analog Ground
Level Adjust. This line can be used to adjust the output
power level of the transmitter. Connecting to ground will
give the highest output, while placing a resistor to ground
will lower the output level (see Figure 7 on Page 3).
50-ohm RF Output
Analog Ground
Supply Voltage
Analog Ground
DATA
Digital Data Input
GND
Analog Ground
Keyed Output
Data In
300-5,000bps
Name
Description
Output Isolation
& Filter
RF Amplifier
Figure 9: LC Series Transmitter Block Diagram
THEORY OF OPERATION
4
LADJ/GND
5
6
7
6
GND
V
CC
GND
ANT
The LC Series transmitter transmits data using Carrier-Present Carrier-Absent
(CPCA) modulation. This type of AM modulation is often referred to by other
designations, including Continuous Wave (CW) and On-Off Key (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 method affords numerous
benefits. Three of the most important are:
1) Cost-effectiveness due to design simplicity.
2) No minimum data rate or mark / space ratio requirement.
3) Higher output power and thus greater range in countries (such as the U.S.)
where output power measurements are averaged over time. (Please refer to Linx
Application Note AN-00130).
The LC Series transmitter is based on a simple but highly optimized architecture
that achieves a high fundamental output power with low harmonic content. This
ensures that approval requirements can be met without external filter
components. The LC Series transmitter is exceptionally stable over time,
temperature, and physical shock as a result of the precision Surface Acoustic
Wave (SAW) frequency reference. Due to the accuracy of the SAW device, most
of the output power is concentrated in a narrow bandwidth. This allows the
receiver’s bandwidth to be quite narrow, thus increasing sensitivity and reducing
susceptibility to near-band interference. The quality of components and overall
architecture utilized in the LC Series is extraordinary in a low-cost RF device and
is one reason the LC transmitter is able to outperform more expensive products.
Page 4
Page 5
THE DATA INPUT
A CMOS / TTL level data input is provided on Pin 2. This line is normally supplied
with a serial bitstream input directly from a microprocessor, encoder, or UART.
During standby, or the input of a logic low, the carrier is fully suppressed and the
transmitter consumes less than 2µA of current. During a logic high, the
transmitter generates a carrier to indicate to the receiver the presence of a logic
‘1’. The applied data should not exceed a rate of 5,000bps. The data input line
should always be driven with a voltage common to the supply voltage present on
Pin 7 (V
CC
) and should never be allowed to exceed the supply voltage.
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, the unit can also be operated from a power supply as long as noise is
less than 20mV. Power supply noise can significantly
Vcc TO
affect the transmitter modulation; therefore, providing
MODULE
a clean power supply for the module should be a high
10Ω
design priority.
Vcc IN
ADJUSTING THE OUTPUT POWER
Depending on the type of antenna being used and the duty cycle of the data, the
output power of the LC Series transmitter module may be higher than FCC
regulations allow. The output power of the module is intentionally set high to
compensate for losses resulting from inefficient antennas that may be used to
realize cost or space savings. Since attenuation is often required, it is generally
wise to provide for its implementation and allow the FCC test lab to easily
attenuate the transmitter to the maximum legal limit for your product.
Two methods of attenuation are available using the LC Series transmitter
module. First, a resistor may be placed between Pin 4 (LADJ) and ground to
achieve up to a 7dB reduction in output power. The resistor value is easily
determined from Figure 7 on Page 3. Do not exceed the resistance values shown
as transmitter instability may result. This method can also be used to reduce the
transmission range and power consumption.
Another method commonly used to achieve attenuation, particularly at higher
levels, is the use of a T-pad attenuator. A T-pad is a network of three resistors
that allows for variable attenuation while maintaining the correct match to the
antenna. It is usually prudent to allow space for the addition of a T-pad. An
example of a T-pad attenuator layout is shown in the figure below. For further
details on T-pad attenuators, please refer to Application Note AN-00150.
A 10Ω resistor in series with the supply followed by a
10µF tantalum capacitor from V
CC
to ground will help
in cases where the quality of supply power is poor.
These values may need to be adjusted depending on
the noise present on the supply line.
Figure 11: Supply Filter
TRANSMITTING 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 LC Series modules do not
incorporate internal encoding or decoding, a user has tremendous flexibility in
how data is handled.
CIRCUIT
ANT
R1
R2
TYPICAL LAYOUT
WITH PROVISION FOR ATTENUATION
If you want to transfer simple control or status signals, such as button presses or
switch closures, and your product does not have a microprocessor on board, or
you wish to avoid protocol development, consider using an encoder and decoder
IC set. These chips are available from a 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,
such as the Microchip PIC, or one of many IR, remote control, or modem ICs.
ANT
GROUND PLANE
ON LOWER
LAYER
PADS FOR SMD
RESISTORS
R1
GROUND
GND
ANT OUT
It is always important to separate what types of transmissions are technically
possible from those that are legally allowable in the country of intended
operation. While the LR Series is ideally suited to the long range transfer of
control and command information, it can also be used with great success for the
transfer of true variable data such as temperature, pressure, or sensor data.
However, the 260 - 470MHz band in which the module operates is regulated by
Part 15, Section 231 of the FCC regulations. Many types of transmissions,
especially those involving automatic transmissions or variable data, may need to
be periodic. You may wish to review Application Notes AN-00125 and AN-00140
along with Part 15, Section 231 of the FCC regulations for further details on
acceptable transmission content in the Unites States.
Figure 10: A T-Pad Attenuator Layout Example
Another area of consideration is that of data structure or protocol. The data
should be formatted in a predictable way and should be able to deal with errors
due to interference. This will ensure that the data is received and interpreted
correctly. If you are not familiar with the considerations for sending serial data in
a wireless environment, you will want to review Application Note AN-00160.
Page 6
+
10μF
Page 7
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, we suggest you read Linx
Application Note AN-00160.
Errors from interference or changing signal conditions can cause corruption of
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.
TYPICAL APPLICATIONS
The LC Series transmitter is ideal for the transmission of remote control /
command data. One of the easiest way to transmit on / off data or switch
closures is to use an encoder and decoder. These ICs provide a number of data
lines that can be connected to switches or buttons or even a microcontroller.
When a line is taken high on the encoder, a corresponding line will go high on
the decoder as long as the address matches. The figure below shows an
example using the Linx MS Series encoder.
750
1
8
GND
GND
2
7
DATA
VCC
3
6
GND
GND
4
5
LADJ/GND ANT
0
0
TXM-xxx-LC
OPEN
100k
100k
INTERFERENCE CONSIDERATIONS
The RF spectrum is crowded and the potential for conflict with other 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 will produce noise and hashing on the output and reduce 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 it is 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, thus, shorter useful distances
for the link.
Page 8
220
1
2
3
4
5
6
7
8
9
10
D6
D5
D7
D4
SEL_BAUD0
D3
SEL_BAUD1
D2
GND
VCC
GND
VCC
GND
D1
TX_CNTL
D0
DATA_OUT
SEND
MODE_IND CREATE_ADDR
20
19
18
17
16
15
14
13
12
11
100k
100k
100k
100k
100k
100k
220
100k
LICAL-ENC-MS001
Figure 12: Typical Remote Control Example
This circuit uses the LC Series transmitter and the MS Series encoder to transmit
button presses. The MS Series has eight data lines, which are connected to
buttons that will pull the line high when pressed. When not used, the lines are
pulled low by 100kΩ resistors. The encoder will begin a transmission only when
the SEND line is taken high. Diodes are used to pull this line high when any data
line is pulled high while isolating the data lines from each other.
The MS Series Encoder Data Guide explains this circuit and the many features
of the encoder in detail, so please refer to that document for more information.
A 750Ω resistor is used on the LADJ line of the transmitter to reduce the output
power of the transmitter. This is appropriate for some antennas, but may need to
be adjusted depending on the design. Typically, a resistor pad will be placed on
the board and a potentiometer used by the FCC test lab to adjust the output
power to the maximum legal limit. The potentiometer value would then be
measured and the closest standard value resistor placed for final testing.
If the level adjust resistor does not provide enough attenuation, a T-pad
attenuator can be placed between the transmitter and antenna. This is a network
of three resistors that will provide a set amount of attenuation while maintaining
a 50Ω match between the antenna and the transmitter. Application Note
AN-00150 gives the formulas for calculating the resistor values. If not needed,
the series resistors can be zero ohms or shorted and the parallel one not placed.
Page 9
ADI Reference Circuit
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