TXM-315-LC ETC2
Document overview
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Technical content
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. LC SERIES TRANSMITTER MODULE DATA GUIDE WIRELESS MADE SIMPLE® Revised 1/28/08 Figure 1: Package Dimensions 0.360" 0.500" 0.150" Max. TXM-418-LC RF MODULE LOT 2000 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 APPLICATIONS INCLUDE 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
FEATURES
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.
ORDERING INFORMATION
Figure 8: LC Series Transmitter Pinout (Top View) Pin #Name Description 1GND Analog Ground 2DATA Digital Data Input 3GND Analog Ground 4LADJ/GND 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).
5 ANT50-ohm RF Output
6 GND Analog Ground
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). THEORY OF OPERATION 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. Output Isolation & Filter RF Amplifier Keyed Output Vcc SAW Oscillator Data In 300-5,000bps 50Ω RF OUT (ANT) Figure 9: LC Series Transmitter Block Diagram
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. 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 100kΩresistors. 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 750Ωresistor 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 50Ωmatch 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. 100k 100k 220 100k 100k 100k 100k 100k 100k 100k LICAL-ENC-MS001 SEL_BAUD0 SEL_BAUD1 GND GND GND TX_CNTL DATA_OUT MODE_IND VCC VCC SEND CREATE_ADDR 1011 220 TXM-xxx-LC
8 GND
Figure 12: Typical Remote Control Example 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. 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.
A whip-style antenna provides outstanding overall performance and stability. A low-cost whip is 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 1/2- or 1/4-wave antenna is normally employed. Its size and natural radiation resistance make it well matched to Linx modules. The proper length for a straight 1/4-wave can be easily determined using the adjacent formula. 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. Linx offers a wide variety of specialized antenna styles. 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. Whip Style Loop Style L =234 FMHz Where:L = length in feet ofquarter-wave length F = operating frequencyin megahertz Specialty Styles A loop- or trace-style antenna is normally printed directly on a product’s PCB. 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 SWR at the desired frequency, which can cause instability in the RF stage. Linx offers low-cost planar and chip antennas that mount directly to a product’s PCB. These tiny antennas do not require testing and provide excellent performance in light of their small size. They offer a preferable alternative to the often-problematic “printed” antenna. COMMON ANTENNA STYLES There are literally 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, and AN-00500. Linx antennas and connectors offer outstanding performance at a low price. ONLINE RESOURCES Latest News Data Guides Application Notes Knowledgebase Software Updates If you have questions regarding any Linx product and have Internet access, make www.linxtechnologies.com your first stop. Our website is organized in an intuitive format to immediately give you the answers you need. Day or night, the Linx website gives you instant access to the latest information regarding the products and services of Linx. It’s all here: manual and software updates, application notes, a comprehensive knowledgebase, FCC information, and much more. Be sure to visit often! www.antennafactor.com The Antenna Factor division of Linx offers a diverse array of antenna styles, many of which are optimized for use with our RF modules. From innovative embeddable antennas to low-cost whips, domes to Yagis, and even GPS, Antenna Factor likely has an antenna for you, or can design one to meet your requirements. www.connectorcity.com Through its Connector City division, Linx offers a wide selection of high-quality RF connectors, including FCC- compliant types such as RP-SMAs that are an ideal match for our modules and antennas. Connector City focuses on high-volume OEM requirements, which allows standard and custom RF connectors to be offered at a remarkably low cost. www.linxtechnologies.com
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 your completed product. 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 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 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. Linx offers full EMC pre- compliance testing in our HP / Emco-equipped test center. Final compliance testing is then 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 your completed product has passed, you will be issued an ID number that is to be clearly placed on each product manufactured. Questions regarding interpretations of the Part 2 and Part 15 rules or 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 21046 Phone: (301) 725-1585 Fax: (301) 344-2050 E-Mail: labinfo@fcc.gov International approvals are slightly more complex, although Linx modules are designed to allow all international standards to be met. If you are considering the export of your product abroad, you should contact Linx Technologies to determine the specific suitability of the module to your 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. NOTE:Linx RF modules are designed as component devices that require external components to function. The modules are intended to allow for full Part 15 compliance; however, they are not approved by the FCC or any other agency worldwide. The purchaser understands that 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. ACHIEVING A SUCCESSFUL RF IMPLEMENTATION Adding an RF stage brings an exciting new dimension to any product. It also means that additional effort and commitment will be needed to bring the product successfully to market. By utilizing premade RF modules, such as the LR Series, the design and approval process is greatly simplified. It is still important, however, to have an objective view of the steps necessary to ensure a successful RF integration. Since the capabilities of each customer vary widely, it is difficult to recommend one particular design path, but most projects follow steps similar to those shown at the right. In reviewing this sample design path, you may notice that Linx offers a variety of services (such as antenna design and FCC prequalification) that are unusual for a high-volume component manufacturer. These services, along with an exceptional level of technical support, are offered because we recognize that RF is a complex science requiring the highest caliber of products and support. “Wireless Made Simple” is more than just a motto, it’s our commitment. By choosing Linx as your RF partner and taking advantage of the resources we offer, you will not only survive implementing RF, you may even find the process enjoyable. 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. As you proceed with your design, you may wish to obtain one or more of the following application notes, 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 the Linx literature department. DECIDE TO UTILIZE RF RESEARCH RF OPTIONS CHOOSE LINX MODULE ORDER EVALUATION KIT(S) TEST MODULE(S) WITH BASIC HOOKUP INTERFACE TO CHOSEN CIRCUIT AND DEBUG CONSULT LINX REGARDING ANTENNA OPTIONS AND DESIGN LAY OUT BOARD SEND PRODUCTION-READY PROTOTYPE TO LINX FOR EMC PRESCREENING OPTIMIZE USING RF SUMMARY GENERATED BY LINX SEND TO PART 15 TEST FACILITY RECEIVE FCC ID # COMMENCE SELLING PRODUCT Typical Steps For Implementing RF 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 NOTE APPLICATION NOTE TITLE
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