Electronic – Why do some Integrated Circuits get so hot

You probably already know that a person can be an expert at using a chainsaw, without knowing much about designing a custom chainsaw, and vice versa. It's the same with chips.

• Are you looking for the basics of using off-the-shelf CPUs in a custom circuit? I would start looking at the Arduino and Parallax Inc. websites, and the rough draft of "Wikibooks: Embedded Systems".

• Or are you looking for the basics of using simpler off-the-shelf digital integrated circuits? Pick up Horowitz and Hill "The Art of Electronics", or Maxfield "BeBop to the Boolean Boogie". Perhaps also skim through the extremely rough drafts Wikibooks: Electronics: Digital Circuits Wikibooks: Practical Electronics Wikibooks: Circuit Idea Wikibooks: Digital Electronics. At the moment, those rough drafts are unnecessarily confusing, but I hope you and others will be able to make them much better. I would start with a solderless breadboard, a breadboard power supply, a bunch of LEDs and a 150 Ohm ballast resistor for each one, and some simple chips -- 74HC132 Schmitt NAND, 74AC153 dual 4:1 mux, 74HC595 shift register. Hook them up, make the lights blink. In principle, with sufficiently large numbers of 4:1 mux chips, you can build any conceivable digital circuit. Dieter Mueller designed most of a CPU using only 4:1 muxes. -- "Multiplexers: the tactical Nuke of Logic Design".

• Or are you looking for the basics of designing your own custom integrated circuits and CPUs? This is usually considered a very advanced topic, requiring learning simpler digital gates first. I've never designed a custom chip, but I thought Weste and Eshraghian "Principles of CMOS VLSI Design" was pretty interesting; also Wikibooks: Microprocessor Design.

• 1. How many "layers" does a microprocessor have?

There is only one layer of transistors. Most transistors are fabbed in a process that uses 3 layers of metal for interconnect. The year 2000 AMD Athlon Thunderbird has 6 interconnect layers, and more recent AMD and Intel processors use a few more layers.

• 2. I remember reading that distributing the "clock" is a big issue for the power usage and design of a chip. Must all parts of a chip run on the same clock?

Nearly all CPUs, and most digital ICs in general, are designed using tools that "enforce synchronous design practices", using a single global clock.

However, a global clock is technically not necessary. There are some globally asynchronous locally synchronous (GALS) chips. A few "clockless CPU" chips have been built, which have no clock at all.

• 2a. Can a "communication channel" be self-synchronizing, like I imagine say a USB/ethernet connection is.

Yes. A few systems (such as clockless CPUs) use completely delay insensitive circuit techniques to stay synchronized, so either end can run at any conceivable rate, down to practically zero.

Many long-distance communication protocols -- USB, Ethernet, CANbus, FireWire, DMX512, ATSC, DVB, etc. -- assume that both ends are running at pretty close to the same rate, and compensate for small differences in rate by using self-clocking signals to compensate for bit-slip, frame desynchronization, etc.

Communication between two ICs on one PCB, or between two sections of one IC, typically uses a dedicated "clock wire" and a "frame wire" running from one to the other to keep everything synchronized.

• 3. Is there software where you can design an integrated circuit, simulate it and see if it works?

Yes. I'm making a list that includes digital circuit simulators

• tkgate open-source gate-level schematic entry and simulator http://www.tkgate.org/
• The Iowa Logic Simulator http://www.cs.uiowa.edu/~jones/logicsim/
• the Tofu relay circuit simulator. http://meatfighter.com/tofu/ http://meatfighter.com/tofu/tutorial/index.html
• FGDIANASYM digital simulator http://www.germinara.it/fgdianasym.htm

Those are all digital gate-level design software. There's a whole other category of transistor-level design software such as "Magic and IRSIM", which is used for full-custom analog and digital IC design.

Electrolytic capacitors should not get too hot otherwise they'll have a tendency to vaporize the electrolyte. This can lead to spectacular results such as the capacitor exploding. Some electrolytic capacitors have notches in their casing to create a controlled explosion, though any explosion will render the capacitor useless.

Most likely you've hooked the electrolytic capacitor in the wrong polarity. Electrolytic capacitors only function correctly when hooked up with the correct polarity (higher voltage on the positive lead). If hooked up backwards, the capacitor will act more like a short circuit and get hot.