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Power versus frequency

  1. Feb 27, 2012 #1
    Can someone please explain to me the truth regarding the generation of a signal at a low frequency versus a higher frequency? I'm led to believe that a simple transistor oscillator operating at say 50 MHz uses MUCH less power than a one transistor oscillator that generates a 2.4 GHz carrier. Is this true and if so why?
     
  2. jcsd
  3. Feb 27, 2012 #2
    Yes and no!!! Yes in most case. Only because at higher frequency, you have to take into a lot more parasitic components that don't matter at 50MHz. Like rise time is hurt by parasitic capacitance in the circuit. Only way to make it fast is the increase the running current of the circuit so it can overcome the capacitance by just charge it faster!!! In idea transistor and circuits, there should not be any difference, but nothing is ideal.

    Even transistors has parasitic capacitance that will speed up with higher running current.

    Does it make sense?
     
  4. Feb 27, 2012 #3
    Yes, so that's the reason for Teflon PCB!
     
  5. Feb 28, 2012 #4
    It's not the dielectric, trace do have impedance that takes power to drive. As frequency goes up, traces start to behave like tx lines and possess finite impedance and it take current to drive it also. Parasitic capacitance of components and others don't help. All in all, higher frequency circuits tends to need more bias current and run in higher current.
     
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