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I using an LT1001 precision amplifier and am trying to plot the open-loop frequency response. As I understand it an op-amp can be modelled as a single poled system:

enter image description here

Which from the LT1001 datasheet has the values: DC open-loop gain = 800,000 Gain-Bandwidth Product = 800,000 Dominant-pole frequency = 1Hz

My query is, is my deduction of the dominant pole frequency at 1Hz correct? Does this mean in the frequency response it will almost immediately start to decrease by 20dB/decade?

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My query is, is my deduction of the dominant pole frequency at 1Hz correct?

It's so very simple - look in the data sheet and see this graph: -

enter image description here

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  • \$\begingroup\$ Great, thank you! \$\endgroup\$ – ConfusedCheese Aug 25 '16 at 10:39
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You are indeed correct here -- the open loop dominant pole frequency on a standard (i.e. unity gain stable compensated) voltage feedback operational amplifier (like your LT1001) is that low, and above that when open loop you get a standard single pole rolloff. What happens is that once the feedback loop is closed, the negative feedback around the amplifier extends the bandwidth in exchange for reducing the gain from its crazy high open loop value. Other parameters (such as output impedance, noise rejection, and distortion) also get poorer with increasing frequency, although most datasheets don't mention this.

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  • \$\begingroup\$ Great, thank you! \$\endgroup\$ – ConfusedCheese Aug 25 '16 at 10:39

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