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The target audience for this post is digital system design engineers; knowledge of digital design is assumed.

What are clock domains?

When they first became an issue, clock domain crossings (CDCs) were determined by the inability of static timing analysis (STA) tools to determine the timing relationship between two individual signals. To a certain extent, that’s still true. The problem is one of scale. When you only had one clock, the problem did not exist. When you had two or three clocks, the problem was manageable as a small number of exceptions. When you have dozens or hundreds of clocks, CDCs are no longer exceptions; there are just too many of them.  Read the rest of this entry »

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Computers operate by Boolean logic, invented by the 19th century English mathematician George Boole. Everything is done with base 2, so there are only the numerals one and zero, or true and false. The three basic operations are invert (the output is the opposite of the input), AND (true only if all inputs are true), and OR (true if any input is true). It’s possible to express any arithmetic function in terms of Boolean logic, and to translate back and forth from base two to base ten. From the biggest computer to the smallest calculator, this is what’s happening behind the scenes.
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Transistors are formed by diffusing different dopants into silicon in specific patterns. Circuits are formed by connecting transistors to one another with wires. Integrated circuits are single pieces of silicon having many transistors with networks of aluminum or copper traces acting as wires to connect them. The transistors and wires are formed by laying down patterns of different substances, layer upon layer. Read the rest of this entry »

A transistor is often described as a switch, but this is only partially true. It’s more like a valve or a faucet. If your faucet has only two choices, “on” and “off,” then it behaves as a switch, but most faucets have a range in the middle, and so do most transistors. If the range in the middle is used, we say the transistor circuit is analog. If all that’s used is “on” and “off” then it’s digital. Read the rest of this entry »

We’ve all heard the cliche that the world of electronic things is “going digital,” but what does that mean? If it’s “going digital,” where is it coming from? What it’s coming from is analog. You may be familiar with the word “analogy” meaning to explain something by comparing it to something more familiar. Analog represents the real world directly. It is continuous and interpolated. Read the rest of this entry »