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I am getting myself confused, I kind of understand decoupling around chips, like you place a small ceramic capacitor on the supply to a chip as this acts like a low pass filter getting rid of any noise or spikes.
I generally see 0.1uF for this cap and then larger ones on the supply rails,I just don't understand how you spec these supply caps, like what formulas do you use. For example how did the admin arrive at the value he has for the large caps on the axon?
There must be a mathematical way of deciding on what supply cap to use though even though no one does, it can't just be trail and error surely?
So if I built say a microcontroller development board you suggest I build it and then max it out with software while checking it with a scope?I'm a little confused on the process here, I need to build before I design...chicken and egg:(
Analog issues in digital circuitsDigital circuits are made from analog components. The design must assure that the analog nature of the components doesn't dominate the desired digital behavior. Digital systems must manage noise and timing margins, parasitic inductances and capacitances, and filter power connections.Bad designs have intermittent problems such as "glitches", vanishingly-fast pulses that may trigger some logic but not others, "runt pulses" that do not reach valid "threshold" voltages, or unexpected ("undecoded") combinations of logic states.Additionally, where clocked digital systems interface to analogue systems or systems that are driven from a different clock, the digital system can be subject to metastability where a change to the input violates the set-up time for a digital input latch. This situation will self-resolve, but will take a random time, and while it persists can result in invalid signals being propagated within the digital system for a short time.Since digital circuits are made from analog components, digital circuits calculate more slowly than low-precision analog circuits that use a similar amount of space and power. However, the digital circuit will calculate more repeatably, because of its high noise immunity. On the other hand, in the high-precision domain (for example, where 14 or more bits of precision are needed), analog circuits require much more power and area than digital equivalents.
This topic reminded me of this article (somewhat off topic since its about resistors). It talks about using resistor triads to replace resistor values that have been selected in test. It's worth a quick read and includes sample code for a program to select appropriate resistors that best fit the target value.
Soeren, you mentioned a buffering capacitor on every digital IC almost in every computer circuit, acting as a buffer. And here is something I don't understand ever since I started the practical part of electronics and runned into the same buffering caps, to this very day. By what logic do we need them??Those circuits already have a filtering capacitor between the supply lines that handles the spikes,
adding any additional caps in paralles will just increse the overall capacitance between the supply lines..
Why for heavens sake buy all those additional caps and increase the total cost of manufacturing??