dberning wrote:
Good article, Walt.
And yes, Paul, lots of RF stuff can be observed on a scope with 100 or so MHz bandwidth.
Incidentally, wide-bandwidth filters are tricky to do. You can't just have one large inductor and one cap to ground to make a good filter. You have to generally have several inductors optimized for different areas of the spectrum. Caps themselves all have resonances too. You need to dissipate the energy in resonances, otherwise a simple ideal cap-inductor combination will simply resonate stronger. This is why ceramic caps are more desirable for wideband filters as they are somewhat lossy. Then the ground itself is problematic as it has its own inductances.
Amplifiers that use high feedback can be very susceptible to RF problems since the feedback breaks down at high frequencies as the open-loop gain goes to pot. To successfully use high feedback in a high-frequency environment, very careful attention to input filtering must be done. With careful filtering, the feedback is not asked to force the amp to linearly reproduce the an input signal with RF components.
I have to pay attention to a lot of this stuff as I use switching power supplies and the output-transformerless ZOTL I use generates RF switching noise as well. But it is possible to deal with it successfully.
David
David's response is exactly what I expected and was not surprised when he pointed out that his amplifier design could actually exacerbate the problem. Of course like everything electronic there are ways to address issues.
Login
Register
FAQ
Search
