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  • EEVblog #572 – Cascading Opamps For Increased Bandwidth

    Posted on January 25th, 2014 EEVblog 10 comments


    Fundamentals Friday.
    Dave explains Gain Bandwith Product and how it’s possible to increase your system bandwidth by cascading opamps in series. Also, a discussion on the associated noise issues.
    A breadboard example shows how variable GBWP can be, and how it can relate to distortion.
    Opamp Noise Tutorial
    Forum HERE

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    10 responses to “EEVblog #572 – Cascading Opamps For Increased Bandwidth” RSS icon

    • Long time waiting for a FF.
      Very good video!!

      Thanks a lot

      • Dave only cleared a path to his whiteboard a couple of weeks ago :).

        What causes the bandwidth of the cascaded sections to fall off? I mean, I understand with a 1MHz GBWP op-amp, going from x100 to x10 increases the bandwidth from 10kHz to 100kHz, but why does adding aonther 100kHz gain stage reduce the entire bandwidth to 64kHz?

        • The output of the first stage at 100KHz is already attenuated, so that already attenuated signal gets attenuated again by the next stage.

        • Yes, the trick to understanding this, is that the bandwidth of an amplifier usually isn’t the highest frequency where the output is not attenuated, but the frequency where it’s 3dB down.

          Put two of them behind each other, and it’s going to be attenuated by 6dB at that frequency. The -3dB point will be at a lower frequency for the combination.

    • Love Fundamentals Friday. So happy you brought it back.

    • Thank you Dave, you have no idea how much we appreciate Fundamental Fridays… I have learnt SOOO much from them. Just keep going :)

    • Peter K├Ârner

      Nice to see you being able to get to the whiteboard again :)

    • Why not three stage in 4 x 5 x 5? Admittedly not as good as 4.6whatever ^3, but much more practical to actually use.

      Or even 2.5 x 2.5 x 4 x 4, if you use 2 dual or one quad opamp.

    • Working out the E96 resistors for crazy gains is easier if you use a resistor calculator, I wrote some here for people to use (under the resistor section)(http://cladlab.com/electronics/general/online-calculators).

      • Yes, it’s not hard with a purpose calculator, but the point is for an irrational number you always get a dicky value. It might be within spec, but it still gives me the heebie-jeebies.

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