I love Bluetooth. It's a great technology that enables you to connect lots of gadgets together without wires and exchange data between them. I had a cheap USB-Bluetooth dongle plugged into my PC that worked, but kept on giving weird errors at random times, so I decided to get rid of it and buy a new one, which fortunately isn't a big investment these days. This also gave me a nice opportunity to examine a modern higly-integrated wireless controller chip: Broadcom's BCM2035!

This is what the dongle looks like on the inside. It's so small that it makes the USB connector look huge! On the PCB we find the main controller, with a few discrete components (mostly capacitors), a couple of small support chips (probably amplifiers and power regulators), and a PCB antenna on the far left. There's also a small EEPROM on the other side that holds the dongle's hardware ID number.

The chip itself is divided into two main parts: a block of digital circuitry at the bottom and the RF transceiver at the top.This picture shows a little more than one quarter of the whole thing.

This is the other corner. There are a lot of on-chip inductors: round or square spirals made of interconnect metal. Normally IC designers use only transistors, resistors and capacitors to build their circuits, because inductors are difficult to work with. Especially for low frequencies, inductors tend to be extremely bulky, but when working at gigahertz frequencies like Bluetooth's 2.4 GHz, their size becomes manageable. Having inductors usually allows a designer to build much better circuits, and that's what they've done here. A quick count shows no less than 18 inductors on this tiny piece of silicon!

This is what we find in the digital area: nothing interesting. At least at this level of magnification...

...so let's return to the analogue part. This is a closer look at one of the inductor circuits. This circuit may be an oscillator, a mixer, an amplifier, or any other part of a radio. It's hard to tell from a photo, because we can only really see the inductors: there are several transistors in this circuit, but they are too small to be visible.

A closer look at one inductor. This one has six turns, and it's about 0.15 mm wide.

This one's round and has two turns.

At extreme magnification levels (about 1000x) we're just able to distinguish the wiring pattern of the digital part. I think this chip is made in 0.35 micron technology, similar to what Intel used to make their Pentium MMX, Pentium Pro and early Pentium II (Klamath) processors. I don't know what all these little squares are for. Maybe these are areas where the top layer of metal wasn't needed, and they're using these squares to shield the underlying circuits from prying eyes...

Another look at some digital stuff. We can only see one layer of metal here, though there are probably several others below it.

Back to the analogue stuff. This is a circuit between a couple of inductors. It's hard to see clearly because it's several layers below the top. The big squares are probably capacitors. There are transistors at the nodes where the wires are almost touching each other.

This is where three small inductors are joined together. Note that most circuits are symmetrical: this is because high-frequency signals are easier to process differentially, using two opposite (positive and negative) copies of the signal.