Unity gain op-amp output voltage amplitude is less than the input voltage amplitude

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Alin Nicusor Manolache 2023-11-9

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https://ww2.mathworks.cn/matlabcentral/answers/2045240-unity-gain-op-amp-output-voltage-amplitude-is-less-than-the-input-voltage-amplitude

回答： Vinay 2024-9-6，7:28

op_amp_demo.slx

Hello,

I am working on a simulation for a unity gain non-inverting op-amp and I'd like to understand some of its behaviours. The op-amp is parameterized based on TI's LM7301. The non-inverting input is connected to a 5V peak amplitude AC Voltage Source. The inverting input is connected directly to the output.

The behaviour I don't quite understand is this: if the frequency of the AC voltage source is set to 50kHz the output voltage amplitude is the same as the input (5V) but if the frequency is increased to 100kHz or more the output amplitude gradually decreases. The LM7301 has a GBW of 4MHz which means that, when configured for unity gain, the output amplitude should be ~5V from DC to 4MHz, correct? I have attached the .slx file for your reference. Here are some supporting images:

Simulation circuit (simulation time 0.05s):

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Op-amp config:

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Scope waveforms @ 50kHz (output matches input):

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Scope waveforms @ 100kHz (output amplitude is decreased):

I really appreciate your time and patience,

Alin

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Answer 1

Vinay 2024-9-6，7:28

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此回答的直接链接

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Hii Alin,

The distortion observed at higher frequencies, at 100 kHz, is due to the slew rate limitation of the op-amp. The slew rate defines the maximum speed at which the op-amp's output can change in response to a change in the input voltage. If the input signal demands a faster change than the op-amp can provide, the output will not accurately follow the input, leading to distortion.

The slew rate is defined as 2*pi*f*Vpeak.

f = 50KHz: slew rate = 1.57 V/us

f = 100KHz: slew rate = 3.14V/us

To achieve the correct output response, you can increase the slew rate to greater than 3.14 V/us in the block parameters.

Kindly refer to the below documentation of “Band Limited Op-Amp”:

https://www.mathworks.com/help/sps/ref/bandlimitedopamp.html

I hope this resolves your query