Fastest Way to Buy or Build a Simple Impedance Matching Circuit (>10k input, 50Ohm output, DC-1MHz)?

Discussion in 'General Electronics Chat' started by Twigg, Jul 8, 2016.

  1. Twigg

    Thread Starter New Member

    Jul 25, 2015
    22
    1
    Hi all,

    I ordered filters to cut out the ripple noise in a very poorly designed amplifier that I need to work. I didn't have the right equipment around, so I measured the ripple frequency at high impedance (straight into the scope, 1MHz) loading and ordered 50Ohm-matched filters hoping the ripple frequency wouldn't fall below the cutoff when the amplifier was connected to the 50Ohm load. Well, it did. Now I am trying to increase the loading on the amplifier output without losing too much signal due to mismatch. The signal band is DC-1MHz. The ripple occurs in numerous distinct peaks as low as 1MHz up to 12MHz. The filters the amplifier drives cutoff at 1.9MHz, and have 50Ohm input impedance.

    My biggest constraint is time. I have only a few weeks to implement something. I was looking at an IC from Linear Tech (LTC6417), but it looks like it would take a fair bit of time to get it built correctly. I've also looked into impedance matching pads, but everything I find is for 50Ohm to 75Ohm conversion. Can anyone point me in the right direction? What products or parts should I be looking at? Any suggestions are appreciated. Thanks!
     
  2. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
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    If you have power to spare, you can do this with two resistors.
     
  3. Twigg

    Thread Starter New Member

    Jul 25, 2015
    22
    1
    I'm getting set up to to try that with a potentiometer. I'm not sure if I can get enough loading without dissipating too much power. I may get lucky, but what should I look into if I don't get lucky?
     
  4. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
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    If that doesn't work, you can try a simple emitter follower.
     
    Twigg likes this.
  5. Twigg

    Thread Starter New Member

    Jul 25, 2015
    22
    1
    Hi all,

    Thanks to KL7AJ for great suggestions. I went with a slightly different design using a pricier op amp buffer instead of a dual-supply emitter follower, so I could get more quantitative data on the oscillation stability and noise levels. For anyone with similar issues, I went with the ADA4870 op amp from Analog Devices using the feedback components listed in Table 6 of the official datasheet. It's probably overkill, but it saved me time and question marks during the design stage. I haven't implemented yet, for non-engineering related reasons, but I'll post in this thread again if anything comes up. Thanks again to KL7AJ!
     
  6. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
    2,040
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    Glad I could help; your bill is in the mail. :)
     
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