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Question about Fmax (max oscillation frequency)

Discussion in 'Electronic Basics' started by Joe, Feb 11, 2004.

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  1. Joe

    Joe Guest

    Hello, I have a quick question about the maximum oscillation
    frequency.

    I was reading earlier in a paper that the maximum oscillation
    frequency of a transistor is defined as the frequency in which the
    powergain is 0 (i.e. input power = output power).

    I was just wondering why a transistor was considered oscillating if
    it's output power is less than it's input power?

    I've read many papers explaining the Rollett stability factor (K) and
    the Available Power Gain (Ga) but nowhere have I found an explanation
    of why I transistor is "considered" oscillating below fmax.

    As well does anyone know of a decent paper or resources that can
    explain this phenomenom to me?

    Thanks in advance
     
  2. The power gain goes down with frequency, so you have it backwards, the
    output power is above the input power at lower frequencies. If the
    transistor won't work as an amplifier it can't oscillate as any
    oscillations would eventually damp out. You can get stable
    oscillation at the unity gain frequency, unstable oscillation below it
    and damped out oscillation (that will die out) above that frequency.

    --Jeff
     
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