Wireless is everywhere now, miniaturized to an astounding degree.
Recently, I saw a report on a button size gardening gadget - stick it in the soil, it reports on moisture. Bluetooth earphones, etc.
Who's designing these things? In my experience, RF designers are a rare breed, and with the digital market vastly larger, they're even rarer.
I'll guess, the IC have been perfected to the no-brainer level. But still, you need need amps, filters, antenna, plus issues of noise and layout, yes/no? That stuff isn't obsoleted.
I don't work in this area, but I'm curious, so can anyone elaborate on what's going on, from a system viewpoint? What are the chip functions, options, price, trade-offs? In which situations would you reject them, to roll your own?
Is it simple on/off keying, or more sophisticated? Currently, in communications theory, sensor networks are a hot topic, where thousands of sensors are competing for bandwidth, but for mundane consumer apps, I doubt those issues arise.
I'm looking to pick the brains of any gurus here -
Build a general purpose RF block for, say, 2.45GHz BT or 802.11(etc), or whatever. Give it handles to talk with anything (modulations, bit streams, etc.), design and build it on a particular fab process, and like magic, anything incorporating that block will also work. Monolithic inductors can be fabricated with not very good Q at 2.45GHz (I think they usually peak around Q = 10 or 20 around 5GHz), but enough to do "silicon oscillators" and stuff. Voltage regulation (bandgap, or old school buried zener) and temperature compensation are no-brainers, as ICs go. Want a DDS? Just chuck some more IP at it! Then whatever ancillary function (moisture, temperature sensor, etc.) simply plugs into this mess of transistors and functions.
Quite crazy, as all that circuitry is squeezing into a few milimeters of silicon, when a few decades ago it was, well of course it was migrating to thick film before monolithic, but before that, it was all machined cavities, hand-soldered RF transistors, and microstrip everywhere. I suppose Bluetooth would've taken up a whole rack, back in the 70s, and that's assuming the computing power to provide whatever spread spectrum, encoding, error detection, etc. functionality is required.
Tim
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You are right, but seems like someone has solved the RF problems once for each of the useful bands, then its a piece of cake to interface with sensors and one end and display/alarm at the other.
For an example, the tyre pressure monitor systems at 433 MHz. 10 gram package, including battery, you screw on a tyre valve. Monitors tyre pressure and temperature for about 1-2 years of operation. Reports real time, every minute or so, to in-car readout.
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Frequently fails mechanically, causing loss of tire pressure, allows tire shops to charge for a "rebuild kit" whenever they swap a tire, requires a trip to the dealer (or specialized equipment/knowledge) to replace, even with an OEM replacement part.. other than that, they're just spiffy.
Best regards, Spehro Pefhany
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So pretty much like many of the new gadgets on modern cars, something else to go wrong that costs you money, even if you never wanted it in the first place :-(
years ago I was given a box of microwave "plumbing" from what may have been a broadcast engineer. The stuff would have worked with microwaves or hydraulic fluid. The guy who made the stuff seemed to be really good with a jewelers saw, copper pipe, brass discs rods and solder.
I read somewhere that Ford is experimenting with their wheel speed sensors to detect a deflating tire. If they can make that work, it would do away with all the pressure sensors and associated hassles. And yes, I didn't ask for that feature, but you have to admit, it is handy and could save a bundle on a replacement tire. Tom
I remember working on making bluetooth in a "single chip" we had a working radio and build an evolution of an existing SOC to stack on top of it in a single package
Everything worked great when we tested the first samples, but then the software guys started running their code in ROM then the sensitivity dropped
turned out that the ROM being in a different corner of the SOC coupled noise into the radio VCO inductors, but the RAM where the test code was run didn't
o
I worked on one of the very first bluetooth implementations, it was; a DSP, a flash, an FPGA, an RF chip, a saw filter, a whole bunch of passives it was probably 5*5cm PCB fully packed on both sides
In the 1988 to 1990s ish time, there was a story in popular mechanics or popular science about a digital ghost canceler for television signals that bounced off buildings. It was huge PCB made using an array of DSPs and have to have pounds of gold plated ceramic chips on it. It was a pretty looking board, that must have screamed at like 16MHz or something like that.
What would that take these days, to basically subtract patterns from a NTSC signal? A couple chips?
Really I was commenting on the RF stuff. Certainly that seems to work as well as needed. Whether the rest of the design is as good as the RF section is a different kettle of fish.
The aftermarket units using sensors like Tyredog seem to have a learning mode to accomodate sensor changes without special tools.
Personally I would be happy if the system just warned that a tyre is going down, before it wrecks the tyre. Identifying which tyre is at fault is a secondary, and usually very easy, job.
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Most such gadgets have very little RF inside. Todays BlueGoof, Wi-Fi, all digital AM/FM receivers, SRD radios, and 433/900MHz weather station chips are almost all digital with maybe a MMIC RF amp or receiver pre-amp on the PCB. The design is being done by digital chips designers, not RF engineers. However, one place where the RF engineer is required is when the product has to pass FCC certification.
Yes and no. Each of the items you mention are somewhat separate from the basic function of the radio and are most often a purchased part from a company that specializes in the device. It is conceivable, that someone with only a minimal knowledge of RF can assemble a sellable and certifiable product using off the COTS modules and components, including the actual radio. I've cleaned up the design on a few such attempts. To be honest, the problems I fixed were oversights due to lack of experience, which will eventually be overcome by the designer.
I assume by "noise and layout" you mean digital noise trashing the receiver sensitivity. Yes, that happens, but with clever design, careful layout, and decent grounding, such problems can be minimized. (Notice I didn't include shielding). The trick is that traces (wires) radiate, while components do not. By simply reducing the size of the device or PCB to the point where the radiating traces are sufficiently small that they don't radiate enough to matter, many such "noise" problems solve themselves. In addition, the power levels found on todays radios are much lower than what was common even a few years ago, making noise pickup less of an issue. Clever protocol design also helps. For example, a GPS receiver with a processing gain of
43dB will not have a noise problem until the noise maybe 30dB above the receive signal. Another example is the common 60KHz WWVB receiver, where the 1 baud data rate results in such a narrow bandwidth that the atmospheric noise inside the approximately 3Hz receiver bandwidth is sufficiently low that it can almost be ignored.
No. I can't. I might be able to provide some insight into current trends in a specific product area, but not the entire world of RF design.
Same problem as before. Too broad a question. As I mumbled, it is possible to assemble a working product out of COTS (commercial off the shelf) parts and pieces. Some volume production areas have been heavily integrated, with plenty of mostly working chips available. Others are specialty products, which are less well integrated. Today, I would roll my own only when I have the projected volume to justify a custom design, or when I want to protect the IP with a custom chip.
There's quite a bit of OOK (on-off keying) modulated products available. TV remotes, WWVB receivers[1], wireless weather stations, car security dongles, etc. OOK has the advantages of being very low power, cheap, simple, and reliable. Sensitivity and efficiency (bits/baud) are terrible, but for many applications, you don't need the speed.
Sensor mesh networks add a new set of challenges. The search for the ultimate routing protocol for store and forward mesh networks is the holy grail of sensor knotworks. This brings the level of complexity well beyond the RF level and into the realm of queuing theory and statistics. There's also the problem of scaling mesh networks. Too few nodes, and the path could easily dead end. Too many and mutual interference, loops, airtime consumption, and bottlenecking near the backhaul point become issues. Incidentally, one of my favorite tests with mesh networks is to put all the nodes in one room, turn them all on, and try to pass some data. I've seen some that fall over badly where nothing moves. They're not competing for bandwidth, but rather for air time. As long as all the devices are using the same frequency hopping code and RF channel, only one radio in view can be transmitting at the same time.
As for "mundane" consumer apps, Wi-Fi mesh networks have all the problems of sensor networks with the added enjoyment of multiple incompatible protocols, overkill tx power, monster antennas, and plenty of possible interference sources.
Sure, but try to be more specific. What are you trying to accomplish?
[1] Yes, I know that it's not really OOK because the carrier is reduced by 10db at the beginning of each UTC second.
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Jeff Liebermann jeffl@cruzio.com
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In countries still using analog TV, the UHF final amplifier is often implemented with klystron in the 100 kW range. The waveguide is quite large, due to the low frequency.
DVB-T digital TV transmitters typically operate with only 1-10 kW, consisting of multiple redundant solid state modules, so there is not much need for waveguides any more.
As much to do with frequency as power level. I've recently completed the design of a Ka band transceiver for satellite (30GHz uplink, 20GHz down). It is a domestic product for delivery of broadband to rural areas. All of the internal RF filtering is done in waveguide, as is the external combining of the transmit and receive signals into a single horn. The transmitter power is just 3W.
How do you get that to the antenna without waveguide? Coax losses are much higher than waveguide, and is less likely to have problems since there is no dielectric to break down.
Heliax for 10 KW? Ever had the filter fail on the compressor and get water in Heliax? I had a stupid SOB for a boss 30 years ago who was too sheap to replace filtes on schedule and ruined a piece of 3" Heliax used at 4 GHz. Waveguide is better at high power, and better than Heliax. I had over 1700 feet of it at one TV transmitter. It carried about 195 KW of RF to the top of the tower. We had to maintain a set pressure of dry nitrogen on the waveguide to keep from compressing the sync pulses.
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