About cascade several RF amplifier

Discussion in 'General Electronics Chat' started by JiaZheng, Apr 1, 2013.

  1. JiaZheng

    Thread Starter New Member

    Jan 28, 2013
    20
    0
    Hello everyone. I dont know to cascade several RF amplifiers (such as this MAX2611) directly (just use a coupling capcacitor to isolate thems) is good or not. Will it be very sensible to noise and easy to oscillate? will the common power supply will provide the path for signal's return to cause oscillation? Rf cricuitry is really hard to design...I searched a lot but seldom to talk about using an IC for cascading. Most are using transistors.

    The reason to cascade is because my detecting signal's power is only -60dBm detected by 50 ohms spectrum analyser (so Vpp is only 0.6mV approximately). I need to amplify it and feed it to comparator for zero-crossing detection and comparator's input I think it should be at least 50mv to provide a good detection.

    This link is the data sheet of max2611. The gain is only 18dB (so 0.6mv becomes 6mV approximately). I need to amplify it again.

    http://docs-asia.electrocomponents.com/webdocs/0ac4/0900766b80ac4985.pdf
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,649
    2,348
    Hello,

    You can cascade a couple, when you have the amplifiers in separate compartiments.
    As long as the input and output can not "see" each other oscillations will be reduced.

    You could also have a look at the MAR8 MMIC, wich has a higher gain:
    ERA and MAR MMIC's

    Bertus
     
    JiaZheng likes this.
  3. JiaZheng

    Thread Starter New Member

    Jan 28, 2013
    20
    0
    Thank you bertus.
    I notice that most RF amplifiers need a bias voltage at the OUTPUT. As you said, preventing input and output to "see" each other, so I should not use single supply (voltage regulator) to bias these several amplifiers altogether but using different supplies to bias them. But it seems wasteful.

    I also notice there is a RF choke in series with the supply. Is it useful for resist high frequency signal to flow into power supply so that I don't need to use several power supplies.
     
  4. JiaZheng

    Thread Starter New Member

    Jan 28, 2013
    20
    0
    WOW, MAR-8+ has 30 dB gain. That's high enough to me. Thank you bertus.
     
Loading...