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straight to the problem. Here is a picture of frequency response of my amplifier in the simulator (LTspice or Pspice both give same results).

enter image description here

Normally, in the open loop i see a phase of 90° which normally tends to increase. In this simulation I see a phase that starts at 180°.

Generally, an amplifier that does not oscillate, when the band touches zero, the phase is not more than 180 °. So, is this amplifier an oscillator, or is it the other way around?

EDIT: This is the frequency response bypassing the input capacitor.

enter image description here

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  • \$\begingroup\$ Normally, in the open loop i see a phase margin of 90° which normally tends to increase A phase margin is a single number (at 0dB gain, the distance to 180 degrees) so how can it "tend to increase"? Also: include your schematic! \$\endgroup\$ – Bimpelrekkie Oct 22 at 12:25
  • \$\begingroup\$ Why two figures - each with four graphs? It is normal that the loop gain starts with a phase shift of -180deg - this means that you have dc negative fedback, which is necessary for a stable amplifier. \$\endgroup\$ – LvW Oct 22 at 12:30
  • \$\begingroup\$ @LvW See on the graphs: 'green' is Open loop response, 'red' is closed loop response. Dashed line is the phase, joint line is the gain. \$\endgroup\$ – N. Bun Dem Oct 22 at 12:34
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No, but it might have a little bit of ripple in it at 10MHz, the ripple will be small at -10dB is equal to 0.316 of gain, so a 10mV input frequency at 10MHz would then be 3.16mV of ripple.

These 'bumps' in the amplifier frequency response are usually from parasitic values in the component or the feedback components.

You could put another pole in the feedback path to get a -40dB/decade instead of -20dB/decade

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