I'm working on a project that requires at least 40 dB gain at 40kHz. I originally used one non-inverting amp using 10k and 1k resistors for a gain of 11. Using cascading rules for linear systems, I cascaded another non-inverting amp of the same gain.

Below is the simulation and circuit that I am trying to implement.

SPICE model of HPF with 2 non-inverting amps with GBW=1 MHz

SPICE Simulation

I implement this system using the LMC662 Dual Op-Amp Datasheet: https://www.ti.com/lit/ds/symlink/lmc662.pdf?ts=1602456193412&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FLMC662

When I run each amplifier separately using Analog Discovery 2 and waveforms, I get the expected frequency responses as shown below.

Scope of one amplifier

But when I cascade it, I get a funky response like this:

enter image description here

Why does this not work as expected?

Note: The High Pass Filter is only being used to simulated a receiver system whos frequency response mimics and band pass


1 Answer 1


I have found the issue but can use some explanation. The amplitude of the input wave for the frequency sweep was too high. Does this cause the op-amp internal transistors to saturate which is why there is a random drop in the response?


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