"high loaded Q". Could anyone explain what this means?

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Nixphe

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Hello,


I'm reading a book on oscillator design. First they analyse the open-loop system, then they talk about phase/amplitude mismatch. You're peak in magnitude not corresponding to your phase. They suggest different oscillator architectures and there suddenly the term "high loaded Q". Could anyone explain what this means?


Thanks!
 

If you take an inductor as an example, its Q is dependant on the equivalent series resistance and reactance at a particular frequency. When you put it in a real circuit there will often be some resistance in parallel with the inductor. This reduces the Q. It is the 'loaded Q'.

Keith
 
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    Nixphe

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Thank you very much!
 

Loaded Q means how strong is your resonator coupled to your circuit. High loaded Q means your resonator is weakly coupled to your circuit. Since the unloaded Q of your resonator must be higher than your unloaded Q, you may have to change the resonator with higher unloaded Q in order for your design to work.
 

QL = F0/(3dB BW) of a tuned or resonant circuit.
For lossless series resonator QL = X/2.Z0
For lossless parallel resonator QL = Z0/2.X
 

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