Connect with us

Mis-matching & matching (was Dumb question...)

Discussion in 'Electronic Basics' started by billcalley, Apr 12, 2007.

Scroll to continue with content
  1. billcalley

    billcalley Guest

    Hi Guys,

    From what I have been able to absorb now from all of your really
    terrific responses is that it is totally and completely impossible to
    LC match, even theoretically, a purposefully mis-matched active
    device*, and then look back into that mis-matched network and see a
    perfect 50 ohms. However, the purposefully mis-matched active device
    WILL get to see the impedance it wants to see. And all this is due to
    the reciprocal nature of LC matching networks. Thus, it would be
    wise, as you have all mentioned, to design any non-50 ohm LNA or PA to
    be as close to 50 ohms as possible, or to design the next connecting
    stage so that it properly works with something other than 50 ohms --
    'cause there is no way to "fix" this mis-match issue with a LC
    matching network. Is that correct, or have I misunderstood
    something? (I can't believe I didn't know -- or didn't understand --
    this stuff from the get-go! A major glitch in my knowledge-base,
    that's for sure.)

    Many Thanks,

    -Bill

    *The mis-match created so as to optimize an LNA transistor's input for
    NF, or a PA transistor's output for P1dB, to name two common reasons.

    (HAD TO OPEN-UP A NEW THREAD BECAUSE GOOGLE GROUPS APPARENTLY REFUSED
    TO POST THIS, EVEN AFTER TWO TRIES -- OR AT LEAST IT DID NOT SHOW UP)
     
  2. Joerg

    Joerg Guest

    Bill, your original post did show up, twice. I don't use Google Groups
    but sometimes I search groups via Google. The results are a bit mixed
    lately, used to be 100% accurate but no more after they "fancified"
    their GUI.
     
  3. Mark

    Mark Guest

    yes I think that is correct for reciprocal matching networks i.e
    standard L C or transformer..

    you can do it with pads but it makes no sense to use pads in this
    application..

    I did think of another way, CIRCULATORS are non-reciprocal devices, so
    in theory you CAN do it using a circulator... but a circulator is
    probably not practical for your application. The theory is
    interesting, you may want to read up on them... but for your
    application you probably just need to compromise the match between
    noise figure and filter flatness.

    Mark
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-