Connect with us

cascode resonance frequency

Discussion in 'Electronic Design' started by Matteo, May 25, 2007.

Scroll to continue with content
  1. Matteo

    Matteo Guest

    hi all
    I'm trying to design a cascode amplifier in resonance, here is the
    schematic:
    http://www.thebags.it/listing/uni/cascode_sc.png

    my project target are:
    gain 20dB
    resonance frequency 850Mhz
    BW 100Mhz


    but I've a problem ..I am not able to set the resonance frequency at
    850Mhz; every combination of C and L I try I always get these
    resonance frequency: 629Mhz, 792Mhz, 997Mhz, 1256Mhz.

    here is a little parametric analysis:
    http://www.thebags.it/listing/uni/plot.png


    how is it possible? I tried to edit all the circuit parameter in order
    to understand the reason but I always get these values


    any help is appreciated!

    thanks

    Matteo
     
  2. Andrew Holme

    Andrew Holme Guest

    It looks like your parametric analysis is only plotting data points at
    those ordinals. The data points do not fall on the true peaks. You
    need to increase the plotting resolution.
     
  3. Matteo

    Matteo Guest

    I was plotting only 10 points per decade! ..I set it to automatic and
    it runs perfectly!
    thank you andrew ..it was driving me mad :p
    matteo
     
  4. Matteo

    Matteo Guest

    I was plotting only 10 points per decade! ..I set it to automatic and
    it runs perfectly!
    thank you andrew ..it was driving me mad :p
    matteo
     
  5. Tam/WB2TT

    Tam/WB2TT Guest

    You really don't want to do it this way, unless you absolutely don't care
    about noise figure, and have a signal that has previously been band limited.

    On the input, you need an LC matching network to match the source to the
    gate input impedance. No physical resistors. Let the resistive part of the
    gate input impedance control the loaded Q.

    On the output, same thing; let the input impedance of the next stage be the
    R.

    Getting 100 MHz bandwidth is going to be difficult with simple 1L/ 1C
    networks. You would need an effective Q of about 8 for the two stages
    combined. Without doing all the math, a Q of 7 on the input and a Q of 4 on
    the output might be close.

    Tam
     
  6. Robert Baer

    Robert Baer Guest

    I believe the term you are looking for is "complex conjugate" matching.
    Something else to look into is "staggered tuning".
    One nice trick is to use an over-coupled transformer; that
    over-coupling widens the (tuned) bandwidth if primary and secondary are
    tuned the same (as i remember from~30 years ago).

    What initially threw me for a loop was C0 and C1 in *Farads*, which
    is insane.
    The second insane thing was that C0 was specified to SIX significant
    digits!!!
     
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

-