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LMH6702: Simulated -3dB bandwidth does not correspond with LMH6702 datasheet

Marco Toffano
Prodigy 10 points
Part Number: LMH6702
Other Parts Discussed in Thread: TINA-TI,

Good morning,

I am contacting you since I was simulating a simple inverting amplifier stage with LMH6702 wideband OpAmp, however the results I obtained seem to be inconsistent with what reported in the datasheet. Specifically, Fig. 2 of the LMH6702 spec sheets claims that for a gain of -10V/V the closed-loop bandwidth of the resulting amplifier should be of 400 MHz, whereas in simulation in TINA-TI (apparently reproducing the same test conditions) I can only get less than 200 MHz.

Of course, transient simulation confirms this behavior for a sufficiently small input signal.

img22222.png

 

img11111.png

Am I missing something? 
 
Thanks in advance for your support.
 
Kind regards,
MT
 
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  • 0
    TI__Mastermind 18165 points

    Hi Marco,

    I was able to confirm this behavior. Unfortunately, this seems to be due to the model and how it is capturing the behavior of this device. Our models are behavioral models, so they try creating different blocks inside the device such as AOL and output impedance and mimic what this would be across frequency. Since they do not capture transistor level design that is in the real device, you get the potential for mismatch in performance when simulating. The LMH6702 brings its own issues since this is a current feedback device adding an additional level of complexity when trying to recreate a behavioral model. For the ac performance of this device, the datasheet would likely be your best reference. If you have any concerns or questions regarding the ac performance you see in the datasheet I am happy to assist.

    Best Regards,

    Ignacio

  • 0 in reply to Ignacio Vazquez Lam1
    Prodigy 10 points

    Thank you very much for your kind response, Ignacio.

    I immediately suspected it could just be something related to the SPICE model of the component. With your confirmation, I think I will just proceed with a very simple test circuit to see if I can reproduce the reported bandwidth and, most importantly, whether the amplifier is stable. 

    Kind regards,

    MT

  • 0 in reply to Marco Toffano
    TI__Mastermind 18165 points

    Hi Marco,

    In general, for most current feedback devices Rf would be your main concern in terms of stability. In this device as long as you are about ~237ohms and above for your value of Rf and have some isolation resistance (if driving a capacitive load) you should result in a stable circuit. Best of luck!

    Best Regards,

    Ignacio