In Reply to: RE: Neutralization of Miller capacitance posted by Tre' on March 11, 2017 at 16:00:06:
searching the forum. I guess what you meant was the post by Lynn Olson (linked below).
Lynn's objection was that neutralization would only work under condition of perfect balance. Any imbalance (e.g. transition into Class B) will cause positive feedback exceeding negative feedback and causing bursts of oscillation.
This is a real problem indeed, but there are at least two ways to mitigate it. First, a differential stage can be forced into complete symmetry (pure Class A) by a CCS or a choke. Second, neutralizing capacitors can be made smaller than Cpg, which will cause partial rather than complete neutralization, but safeguard against excessive positive feedback.
Yet another source of problems could be imperfections in neutralizing capacitors introducing distortion at the critical signal juncture. However, since capacitances in question are relatively low, very high quality capacitors can be used. Vacuum caps come to mind.
This post is made possible by the generous support of people like you and our sponsors:
Follow Ups
- I should have done better - sser2 22:03:06 03/11/17 (4)
- Re. positive feedback and RF oscillation - sser2 17:29:55 03/15/17 (0)
- RE: I should have done better - Lee of Omaha 14:08:41 03/15/17 (2)
- Vacuum capacitors - sser2 17:13:53 03/15/17 (1)
- Wow! - Lee of Omaha 12:01:27 03/21/17 (0)