I have to disagree with my friend and esteemed colleague. A clock and a carrier frequency for a 2.4GHz phone are very similar. At 2.4GHz with clock distribution across tens of millimeters of chip in wires that are thinner than hair, a clock waveform on a chip bears a more striking similarity to a sine wave than a square wave.
The clock route on a chip tends to be very short - relatively speaking. The wavelength of 2.4GHz is about 5" - which means that a clock route could be likened to non-ideal quarter-length dipole antenna. But it's not a very good one. For a start, the magenetic suscepetibility of SiO2 (and similarly the other materials used between wires on a chip) is very low, so the material between the wires on a chip tends not to act much like an inductor. In addition, the width and thickness of the wiring on a chip - even the relatively wide wires used for clock distribution - still result in relatively highly resistive wires. So the small inductive effect that does exist in silicon is dampened out even more. In addition, the spacing of neighboring wires to the clock signal is extremely close, so there is fairly high capacitive coupling (as I unfortunately know all too well) but it is primarily to the signals that neighbor the clock - which are always power/ground tracks by design.
But even so, were the top of a chip open to the world, you would probably be able to measure a nice 2.4GHz signal from the clock. I can't imagine that with the active drivers on the clock route that you could hope to interfere with the clock but I'm sure that you could detect a measureable signal from the chip. But the top of the chip is not open to the world. The top of the chip is covered with round bumps and is then flipped over and attached to a package that contains a whole lot more routing and metal layers. All of this metal in the die and the package acts overall like a Faraday cage.
So if you can imagine an antenna made out of thin metal that is wrapped in a material that makes for lousy inductance that is then surroundeded on two sides by extremely close neighboring wires that are tied to a low-resistance DC signal that is then wrapped in a birds nest of other wires, you can see that the clock of a chip isn't likely to result in interference, nor to be interfered with by outside sources.
I wonder how well you could detect the clock signal by looking at ripples in the power supply though. And power is routed across a PCB which makes a much better inductor than silicon...
It's a good subject for the highly technical forum. It beats debating whether or not the computing and semiconductor industry has made any significant advances in the last 20 years, anyway.
Facebook
Twitter