Electronic Design

What's All This Wireless Stuff, Anyhow?

As Jaye P. Morgan sang 50 years ago, "They all laughed at Wilbur and his brother, when they said that man could fly. They told Marconi, wireless was phony, it's the same old cry."* For over 60 years, I have been enjoying many wireless things. But these days, people think "wireless" is a great new deal.

If somebody invents a wonderful new system with electromagnetic radiation and digital coding, it must be good. "Radio" is obsolete. "Wireless" is wonderful.

Just this morning, I heard Disney head Michael Eisner say that before 1948, there were only three major movie studios, and no television, for entertainment. He seemed to have no inkling that there were several large (and lively) radio networks broadcasting music, news, drama, and entertainment all around this country (and around the world) many years before World War II. People don't seem to pay no respect to radio and other early wireless inventions. (Personally, I think the pictures are better on radio.)

As you may have noticed, National Semiconductor is not a major provider of digital VLSI chips that go into cell phones. So you might say that NSC isn't a player in this wireless market, eh? No, you shouldn't say that!

When the VLSI chips began to get specialized and optimized for high performance in cellular phones, the clock frequencies began to go up, and the logic feature sizes began to go down, as did the power-supply voltages—just like for microprocessors. And what falls out? A magic word! Disintegration.

When you make smaller features and run your VLSI chip on lower voltages, certain functions are hard to do. A decent audio amp can't run efficiently on 1.8 V. Furthermore, a cell-phone amplifier has to reject certain kinds of nasty noise. So a good audio amp for a cell phone works a lot better on a separate chip at 3.3 V. Thus, this disintegration makes an external amp a good idea.

We have many good amps optimized for various cell-phone, portable, and wireless activities, such as the LM4880. (Why do people want stereo amplifiers in a cell phone? Why not use two cell phones, one for each ear? Don't ask.) When your GSM phone has a lot of "bumblebee noise" at 217 Hz, an amplifier like the LM4890 can reject it nicely.

Switching regulators that can convert a wide range of battery voltages efficiently to the needed regulated voltages are never included on the VLSI chip. So we make lots of those regulators, such as the LM3200. Others are used to pump voltages up to go into LEDs and backlights for various displays. If you needed a precision reference, you could integrate it on the main chip. But the yield loss makes this a loser. Do the math. It's cheaper to add a separate chip. There are log-amplitude detectors for the RF power output like the LMV225. There are power-amplifier controllers, too.

Temp sensors for the voltage-controlled crystal oscillators and the output RF power transistors— and for battery recharging—usually do not go on the main chip. The LM20 draws very low power, and there are many other temp sensors optimized for portable use, with analog or digital outputs. After all, the main chip ain't at the same temperature as the crystal, which ain't at the same temp as the battery. A single temp sensor isn't right to do all those jobs. There's a lot of places where cell-phone makers like to use linear chips, just like the digital computer makers do. They just don't talk about it a lot.

So, is wireless really "everywhere?" Not at my house.

* George Gerswin, "They All Laughed," 1937

TAGS: Components
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