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I have been playing around with an op-amp design using TINA from Texas Instruments. I have selected the LM301A. TINA says that this op-amp has a dominant pole at 5 Hz. I have put the circuit below. VG1 is feeding in a 2 Hz sine wave at 50 mA. The supply is \$\pm 5\text{ V}\$. When I simulate this circuit the -3 dB point seems to be around 38 kHz. I am obviously doing something wrong, I just don't see it. Can anyone offer any advice?

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The dominant pole can be seen only in the open loop configuration. When you add negative feedback, gain is reduced and the BW is enhanced (for the closed loop system)

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Op amps which use dominant pole compensation have a constant gain-bandwidth product. You've cited a 5Hz dominant pole, and the LM301A datasheet gives a typical open loop voltage gain of \$160\text{V}/\text{mV} = 160,000\$. This gives a gain-bandwidth product of \$160,000 \times 5\text{ Hz} = 800,000\text{ Hz}\$. You have configured this op amp with a closed loop gain of \$|A_v| = 20\$ so the expected bandwidth is \$800,000\text{ Hz}/20 = 40,000\text{ Hz}\$, which is close to your observed -3dB point of 38kHz.

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  • \$\begingroup\$ Thanks for the reply! It's good to see the maths behind it. \$\endgroup\$ – o.fithcheallaigh Jun 2 '16 at 14:49

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