A classic situation is the use of a pair of bypass capacitors (one tantalum, one disc ceramic), often recommended to improved bypassing. The pair can form a lovely paracitic tuned circuit somewhere in the HF to VHF region (tens to hundreds of megahertz), with self-oscillations!
Note that he says Disc Ceramic. I think what's going on there is that the legs in the caps are making up an inductance, and that the solder is making a bimetal diode junction capable of amplification, and therefore oscillating. SMT Chip caps have far less inductance, and if the board is shaped right, you can damp any oscillations that may appear by spreading out (intentional) parasitic inductance and resistance.
As to your general question of where do we learn this stuff? Some of the information is given in school, some via OJT, some by Forums such as this, and some you stumble across after learning how to ask the right question.
Like grounding, choosing bypass caps can involve some mental gymnastics. Most of the time simple rules-of-thumb can take you a long way...but it's always handy to understand the basics when the ROTs don't pan out.
And make this a sticky? Well, stickies tend to be forgotten or just covered over with other stickies. I would recommend that you bookmark this thread for your own "personal sticky" as it contains good stuff. :thumb:
Comments
... I second that!
Hi sunblock. Here's the other link I wanted to provide:
http://www.intersil.com/content/dam/Intersil/documents/an13/an1325.pdf
As to your general question of where do we learn this stuff? Some of the information is given in school, some via OJT, some by Forums such as this, and some you stumble across after learning how to ask the right question.
Like grounding, choosing bypass caps can involve some mental gymnastics. Most of the time simple rules-of-thumb can take you a long way...but it's always handy to understand the basics when the ROTs don't pan out.
And make this a sticky? Well, stickies tend to be forgotten or just covered over with other stickies. I would recommend that you bookmark this thread for your own "personal sticky" as it contains good stuff. :thumb: