Archive for August, 2010
How to Simplify the Design of an RF Remote Control
Posted by: | CommentsBy Lawrence Der, Wireless Product Marketing Manager, Silicon labs
Remote controls come in many different sizes, shapes and wireless technologies and are widely used in the consumer market as accessories for a wide range of products, such as televisions, video games, stereo systems, lighting controls and home automation including garage door/gate openers, air conditioning units, fans and automobiles with remote keyless entry (RKE) key fobs. The most common remote controls use infrared (IR) technology because of the relatively low cost of IR components, but these IR-based controls suffer from many drawbacks including requiring line-of-sight pointing, limited operating angles, short transmission range, reflection problems and high current consumption associated with the IR LEDs, which leads to low battery life. RF remote controls resolve these issues and are appearing in greater numbers because consumers are demanding a much better user experience. In addition, technology improvements are closing the RF-IR price gap.
Figure 1: Simplified Block Diagram of an RF Remote Control
All RF remote controls share common features as shown in the simplified block diagram in Figure 1. The basic components of an RF remote control are buttons for the user to input a command, a microcontroller unit (MCU) to process the user commands into digital messages, an RF transmitter (RF TX) to modulate and transmit the message, an antenna, and a battery to provide power to the remote control. The common challenges manufacturers face in designing RF remote controls are to provide consistent maximum transmission range, ensure long battery life and maintain low system costs.
Maximizing transmission range involves transmitting as much power as possible (within governmental regulatory limits) while providing a receiver with excellent sensitivity since the total transmit distance is a function of both the transmitter output power and the sensitivity of the receiver. From the remote control side, the design goal is to set the RF output power to the government limit, which implies that all remote controls should have the same output performance, since they all transmit within the same limits. This would be true in an ideal world, but, in the real world with real components and manufacturing tolerances, it is practically impossible to transmit at this optimum power every time with every remote control manufactured on the production line. Moreover, interference from a user’s hand holding the remote control or even touching a button (known as the “hand effect”) changes the impedance of the antenna and thus changes the transmit output power. This real-world effect can reduce the effective radiated power (ERP) of a remote control and easily result in output power 6 dB below the government limit, with a corresponding 2x reduction in transmit distance per Friis’s free space path loss equation. Read more…
RF Receiver Front-End Topologies for Software Radios
Posted by: | CommentsA number of different RF front-end topologies are appropriate for software radios, each with its own advantages and disadvantages. This article explores the tradeoffs involved with each approach.
By Jeffrey H. Reed, Virginia Tech
The most common types of RF front-ends for software radios are dual conversion, single conversion, and tuned radio frequency receivers. The suitability of a particular receiver topology depends on a number of parameters that may include the following.
- Sensitivity defines the weakest signal level that a receiver can detect and is usually determined by the various noise sources in the receiver.
- Selectivity- represents the ability of the receiver to detect the desired signal and reject all others.
- Stability indicates the lack of change in the receiver gain and operating frequency with temperature, time, voltage, etc.
- Dynamic range is the difference in power between the weakest signal that the receiver can detect and the strongest signal that can be supported (either in-band or out-of- band) on the receiver without detrimental effects.
- Spurious response is a receiver’s freedom from interference due to internally generated spurious signals or to their interaction with external signals.
Topologies
Tuned RF
The tuned radio frequency (TRF) receiver, shown in Figure 1, consists of an antenna connected to an RF bandpass filter (BPF). The BPF selects the signal and the LNA with the automatic gain control (AGC) raises the signal level for compatibility with the ADC. This BPF bandwidth relative to the carrier frequency can be quite narrow, while in absolute bandwidth, it may be quite broad. For example, a second-order inductor and capacitor filter would require a filter quality factor of 107 to extract a 30 kHz signal at 900 MHz with 60 dB of attenuation for a channel 60 kHz away, which is highly impractical.
Wireless Sensor Technology for Real-Time Applications
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Battery Life Chart
By Aaron LaJoie, Electrical Engineer, Electrochem Solutions, Clarence, NY.
The ability to make real-time decisions based on pressure, temperature, or flow measurements while a process is running can provide significant advantages in a measurement and control system. These advantages can be expressed in different ways such as cost savings through improved resource management, or reduced reliability upon mobile workers. While measurement data can be used to dynamically control a process, it can also be displayed over a network to allow remote monitoring of the process status in real time. Rising pressures, temperatures, or vibration intensity can easily be adjusted if the appropriate personnel are aware of faulty conditions. As data is collected for process control or a SCADA system, it can also be archived for future reference when a review of process trends could provide additional improvements.
While wireles sensing clearly offers many advantages, the adoption phase moves at a slow pace in many industries due to inaccurate perceptions of the technology. One of the main reasons wireless technology is yet to be fully adopted is price. Many organizations have not taken the time to explore the benefits achieved via wireless sensing in comparison to the price of implementing the technology. Similarly, a company may be content with their existing wired system and be reluctant to make the switch.
Musical Chairs in RF Chip Market
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Guest Blog by Will Strauss, President & Principal Analyst
Forward Concepts
Infineon Bidding War?
It is clear that Infineon has put its cellular handset chip business on the block and rumors are rife on who is bidding and who the likely purchaser will be. In mid-May the Financial Times Deutschland published an article stating that Intel is interested in acquiring the cellular chip properties of Infineon Technologies AG, which provides the cellular modem and RF transceivers for all iPhones and the iPad. Apparently, Intel was initially rebuffed. However, in mid-June, Infineon announced that it had engaged investment banker JP Morgan to study the possibly of selling their cellphone chip business. I guess Infineon realized that they could make a nice profit through such a sale and they could concentrate on the more lucrative automotive market.
By engaging an investment banker, Infineon is certainly interested in getting multiple bids for the cellular business and realizing the highest price possible. Rumors abound that in addition to Intel, Samsung, Broadcom and even Apple are among those in talks with Infineon. I think we can forget the Apple rumor, since even Nokia has decided it doesn’t want to be in the chip design business anymore (see Renesas, below). The asking price has been reported as about Euro 1.5 billion ($1.9 billion), so let’s examine the possibilities:
–Broadcom: The company currently has a very small share of the 3G cellphone chip market, although it has done rather better in the 2.5G market (with Nokia as a major customer) and is a major supplier of ancillary cellphone chips, which include Bluetooth, Wi-Fi and GPS. In the past, Broadcom has paired its 3G baseband chips with Infineon’s worthy 3G RF transceivers, so the two companies are well-acquainted. Infineon’s significant sales of both 3G transceivers and basebands to Apple (perhaps 40% of Infineon’s cellphone chip shipments) would be a major boost to Broadcom’s market penetration. So the only question would be in Broadcom’s possible commitment to such a large investment.
–Samsung: The #2 semiconductor company in the world would like to be #1, displacing Intel. The cellphone market would enable it to quickly expand its revenues in a non-memory market that could eventually rival the PC market. The handset side of Samsung has been a customer for Infineon’s 3G RF transceivers, so that could be additional incentive to acquire Infineon’s cellphone chip business. Samsung could certainly afford the rumored purchase price. However, would LG, Nokia, and even Apple want to buy cellphone chips from a rival cellphone vendor?
–Intel: the #1 semiconductor company has always coveted the communications market, and they realize that wireless could eventually rival the PC market. Moreover, Intel has hopped in bed with Nokia on a number of wireless things, like licensing Nokia’s 3G modem technology and jointly developing MeeGo, the Linux-based operating system that Nokia plans to use in its future E-series handsets for the business market. It appears that the Nokia-Intel modem licensing did not include 3G/HSPA RF transceiver design, something that Infineon is good at (and few others are). Unlike Samsung, Intel would not be seen as a threat by cellphone vendors, and everything points to Intel’s strong wireless ambitions, so we pick Intel as the likely buyer.
Fallout from Infineon Sale?
If Intel purchases the Infineon cellphone chip business what will happen to Comneon, the Infineon subsidiary that licenses 3G/HSPA/LTE software stacks? Intel has never entertained the licensing model as part of its chip business and would likely shutter the Comneon operation, just as Motorola did after they purchased TTPCom’s 3G licensing business. TTPCom’s 3G stack lives on (albeit with much improvement) as a component of Icera Semiconductor’s modems, MediaTek’s new WCDMA modems (via its Analog Devices cellular chip acquisition) and Marvell’s 3G modems employed in a number of RIM BlackBerry models (BTW, is the plural of BlackBerry® BlackBerries?).
There are a number of smallish LTE baseband startups (mostly morphed WiMAX baseband suppliers) that are aiming at the USB data dongle modem market. And, of course, the data dongle market is currently the only LTE terminal market, and will be for perhaps another year or two. For LTE cellphones, fallback to HSPA/3G/2G will be required, since the world will not instantly change over to LTE. Faced with investing an estimated $300 million and many man-years to develop a complete 3G stack, it is likely the only possibility for the new LTE modem houses is to license the technology. The possible sources will likely be narrowed to two: InterDigital Communications (which was a joint developer with Infineon of the Comneon stack) and NTT DoCoMo. DoCoMo announced last week that it had licensed its LTE stack to MediaTek to augment its current 3G/2G stack.
Renesas Rising
At the Mobile World Congress last February, there were rumors that Renesas was soon to get a 3G/HSPA/LTE baseband modem design win at Nokia. When I met with Renesas executives at the Congress, they readily admitted that they were beefing up their Munich operations to better serve Nokia. But the emphasis was on Renesas’ RF transceiver and RF power amplifier chips and every time I asked about a baseband chip, they answered the question, but like politicians, never answering the question that was asked. So, I knew that something was underway, and it’s now clear that Renesas had licensed the Nokia HSPA+/LTE modem IP last year, and Nokia must have liked the progress made by Renesas.
In early July, Nokia and Renesas jointly announced that Renesas was to acquire Nokia’s wireless modem business for $200 million. That acquisition involves transferring 1,100 Nokia R&D professionals who are mostly located in Finland, India, Denmark and the UK (a no-pain layoff?). It appears that Nokia found it too expensive to continue developing its own modem designs and felt that it was more economical to acquire the modem chips from outside sources. The deal is set to close later this year. Apparently, Nokia will continue developing 3G/HSPA+/LTE software, which it will share with its modem licensees, which now also include Broadcom and Intel (who are not presently shipping cellphone modem chips based on the Nokia IP). It’s clear that Nokia will continue purchasing modem chips from Qualcomm, ST-Ericsson, Infineon and Broadcom, so they can get competitive pricing (at least in non-CDMA modems).
You’ll recall that Renesas merged with NEC Electronics’ chip business a few months ago, and collectively, the two only had about a 2% market share in the 3G modem market, mostly based on NTT DoCoMo IP, and selling primarily to Japanese cellphone companies. Now, the Nokia acquisition will enable them to expand out of Japan and be able to provide competitive modem chips on a global basis. Although the “original” Renesas has competitive RF chips, it’s unclear whether the company will continue fielding its original application processors based on SH-DSP or will use the NEC-heritage EMMA chips based on ARM Cortex-A8 and A9 designs; likely the latter, since Renesas had also licensed the Cortex-A8 technology.
Forward Concepts
Tempe, AZ
www.fwdconcepts.com
Email: wis@fwdconcepts.com
Is Cell Phone Radiation a Health Hazard?
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Everyone with a microwave oven knows that radio waves can heat up water molecules, which is handy when you’re making Mac and Cheese for the kids but a little more problematic when you spend hours every day with a cell phone pressed to your ear. Are cell phones a health hazard?
In May the $24 million Interphone study was finally released, after 10 years of study in 13 countries with 13,000 participants. The Interphone study included 2,708 cases of glioma and 2,409 of meningioma, another type of brain tumor, with a total of over 5,634 controls —from 13 countries. Eligible cases were patients diagnosed between 2000 and 2004. (Meningioma was not linked to cell phone use.) It is the largest study of cell phone and tumors ever done.
The point of the study was to determine once and for all whether cell phones represent a health hazard. The conclusion: “Overall, no increase in risk of glioma or meningioma (a specific brain cancer thought to be promoted or triggered by cell phone radiation) was observed with use of mobile phones.” However the report went on to state, “There were suggestions of an increased risk of glioma at the highest exposure” and those tumors are more likely to show up on the side of the head on which the user typically holds the phone.
As one of the researchers said at a press conference announcing the release of the report, “We have not demonstrated that there is increased risk but neither have we demonstrated that there is an absence of risk. These findings of increased risk in the heaviest users suggest a possible association but we don’t have enough scientific evidence.” The results, on the surface, are unclear.
Cause for Concern
On closer inspection the Interphone study isn’t as equivocal as it first appears. If you’re willing to dig through the data, Appendix 2 paints a considerably less nuanced picture than the report itself. As Microwave News points out,
“Although not included in the paper, [Appendix 2] offers a way to look at the risks free of some of the bias that so muddled the published results. It also provides a window on the controversy that deadlocked the Interphone group for four years.”
The report—and Appendix 2—clearly show higher incidence of cancer among “heavy cell phone users”, defined as those using cell phones more than 30 minutes per day—a pretty low number for your average teenager.
“Those who used a mobile phone for ten or more years were found to be twice as likely to develop a brain tumor. This increased risk is statistically significant. Indeed, the risk is higher for all three indices of exposure —years of use, total talk time and total number of calls. There even appears to be a dose-response relationship, with the highest risk among the heaviest users.”
Check out the data below:
Interphone Study Appendix 2
As with any study there are built in biases that need to be factored into any conclusion. “You can see patterns in the data that show some risk, but the issues of selection and recall bias make me concerned,” said one of the study’s researchers. Siegal Sadetzki, the Israeli member of Interphone, told Microwave News, “The data are not strong enough for a causal interpretation, but they are sufficient to support precautionary policies,” she said. Elisabeth Cardis, who leads the Interphone project, took a less equivocal stand: “To me, there’s certainly smoke there. Overall, my opinion is that the results show a real effect.”
The Rush to Legislate
Politicians have been quick to start promoting “precautionary policies.” At the same time some industry groups have been quick to push back.
Specific absorption rate (SAR) is a measure of how RF energy is absorbed by the body. It measures how much tissue is heated up, which is one way that cells can be damaged. In the U.S., the FCC limits legal SARs to 1.6 watts per kilogram. Cell phones vary considerably in output, typically ranging from 0.1-1.5 watts per kilogram. The prudent thing to do is to buy a cell phone with the lowest SAR. Or talk less on the phone and use a Bluetooth headset when you do.
SAR is easy to measure, unlike cell mutations that clearly can cause cancer whereas heat by itself probably doesn’t. SAR is just a proxy for a missing metric. The only way you can determine an RF/cancer correlation is by long-term epidemiological studies like the Interphone study.
In June San Francisco passed its Cell Phone Right to Know Ordinance, mandating that all cell phones sold in the city must clearly show the SAR figure for the phone. This information is available if you look hard enough, but it’s not easy to find. San Francisco just wants it to be front and center so consumers can make more informed decisions.
CTIA defends your right to not know!
That isn’t the way the Cellular Telephone Industries Association (CTIA)—sees it. “The wireless industry is committed to consumer choice,” trumpeted the CTIA, which by Alice in Wonderland logic sees San Francisco as somehow impeding by providing more information upon which to base those choices. The CTIA almost immediately sued the city of San Francisco claiming that hey, all cell phones are safe because the FCC says they are:
“The ordinance challenges the Federal Communication Commission’s (FCC) determination that all FCC-compliant wireless handsets are safe by mandating that retailers post Specific Absorption Rate (SAR) values. The ordinance misleads consumers by creating the false impression that the FCC’s standards are insufficient and that some phones are “safer” than others based on their radiofrequency (RF) emissions… The FCC has determined that all wireless phones legally sold in the United States are ‘safe.’”
There, now don’t you feel better already? Just ignore the quotes around ‘safe’.
SF Initiative Goes National
The CTIA notwithstanding, San Francisco’s ordinance is gaining momentum. On June 30 Rep. Dennis J. Kucinich (D-OH) announced his intent to introduce a bill in congress making an SAR labeling a national law, at the same time establishing a new national research program to study cell phones and health.
“Some studies find links. Some don’t,” said Kucinich.” But studies funded by the telecommunications industry are significantly less likely to find a link between cell phones and health effects. We need a first class research program to give us answers.” Meanwhile, “a labeling law will ensure that cell phone users can decide for themselves the level of risk that they will accept.”
As soon as Kucinich files his bill you can be sure that the CTIA will be in there fighting and suing for your right not to be confused by too much information.
