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This should be interesting, How many people on here will know this, maybe a few, OH well any way What is Nyquist oscillation?, I Know the name just can't relate it to oscillation. And remember negative feedback is not alway bad..
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Nyquest oscillation? Haven’t heard of it. Have heard of nyquest frequency though. If you sample a signal to slow, after reconstructing it there will appear to be incorrect oscillation frequencies.
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Posts: 1259 | From: Fullerton. CA ,USA | Registered: Oct 1999
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quote:Originally posted by Hertz_so_good: For that coughing, sniffling, stuffy head, fever, so you can rest oscillation...
Lol.. yup thats it No actually the nyquist rate of a signal is exactly double the rate of its highest frequency. This is the rate needed to fully retain all signal information. For example, if your signals highest frequency is 200 hz, the nyquist rate would be 400 hz. If it is sampled at anything lower than that, ailasing will result.
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"Self-sustaining oscillation resulting from excessive phase shift in the NFB loop is colloquially referred to as Nyquist Oscillation" (Sloan, pp. 75)
The P1 frequency (where an amplifiers gain goes from linear to frequency dependant, and the global NFB factor drops with gain) under which gain is constant and over which gain is variable.. Above this frequency, the "miller capacitance" of the transistor input stage will interact with voltage gain, putting NFB at a phase shift and inducing self-sustaining feedback into the amplifier if global NFB is used above this frequency.
If the gain drops below unity before such a large phase shift can occur, there is no oscillation, and the P1 frequency (to lower gain as per above) is adjusted using the "CC" capacitor across the base and collector of transistor in the VA stage.. Such adjustment is termed "Miller dominant pole compensation" because you change the dominant pole (P1 freq. ) to compensate for NFB oscillation as frequency and phase shift increase..
So, Nyquist oscillation might be the culprit of the "smear effect" many people complain about when using NFB...?
Thoughts?
ShadowStar
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Posts: 2578 | From: Somewhere In the Northeast | Registered: May 1999
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posted
ahh, you must be learning about transistors as amplifiers + the capacitance of the gates and there relationship to the whole circuit when the capacitances actually start to have and effect. unless you have a really cheap transistor, the capacitance at the gates is so small you can ignore it.
who ever said NFB has a bad rap? NFB is a good thing.
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Posts: 1259 | From: Fullerton. CA ,USA | Registered: Oct 1999
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posted
We started on the Miller effect, but after working througha few examples we came to the conclusion that for audio purposes Mr. Dank is right. Colin
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Well, its got a bad rap in the "subjectivist audio community" ( you know, audible 10,000$ cables and such, amplifiers w/ tubes costing 1k per watt, solid state devices with little NFB (look at eclipse! their audio amps are marketed as low NFB devices..)
ShadowStar
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You can't build a reputation for what you're GOING to do.. But you can build one for TALKING about it!
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It's all about knowledge, love and respect.
Posts: 2578 | From: Somewhere In the Northeast | Registered: May 1999
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posted
I would like to see somebody try to desing an amp with the gain they have and not use negative feedback. I believe its almost impossible without getting oscillations. Negative feedback is the best thing that happened to amplifiers.
Maybe people dont like it because it has the words negative and feedback in it. LOL
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It's not the size of your woofer, It's the size of the waves your woofer makes!
Posts: 1259 | From: Fullerton. CA ,USA | Registered: Oct 1999
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posted
AS dank said, I think people don't like negative feedback because of the name. It's a good thing, improving linearity, distortion. It does affect stability but only if overdone.
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Posts: 768 | From: Ottawa, On, Canada | Registered: May 2000
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