RF amplifier gain. NEED HELP!!!

Discussion in 'General Electronics Chat' started by JiaZheng, Apr 16, 2013.

  1. JiaZheng

    Thread Starter New Member

    Jan 28, 2013
    20
    0
    I tried my best to adjust the circuit components but failed too many times. I tried to cascade two MAX2611 to give me 100 voltage gain but the problem is the oscillation and sometimes the input will be distorted! I have no idea why the signal from the signal generator can be distorted??? It is so strange and why individual amplifier can work but use a coupling capacitor to connect them then oscillation will happen. I don't know what should I do to add somewhat phase margin. Except the ground and voltage regulator I cannot find any feedback path for such oscillation happened. Are there some useful technique to properly isolate amplifiers?

    If I want to achieve 1000 times gain to amplify a -60dBm signal, what should I do?
     
  2. crutschow

    Expert

    Mar 14, 2008
    12,977
    3,220
    An old engineering saying is that oscillators amplify and amplifiers oscillate. High gain, wide bandwidth amplifiers are prone to oscillation since it takes very little stray feedback from the output to input to initiate an oscillation. To counter this you need a good circuit layout on a circuit board containing a ground plane, with good decoupling of the amps (0.1 or 0.01μF surface mount caps connected directly to the V+ pin and to the ground plane) and having any output signal lines as physically remote from the input as feasible.
     
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