op-amp stability | PartQuest™ Explore

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ton.pijpers44
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ton.pijpers44

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Description

This circuit shows the interaction effect between an op-amp's input capacitance and relatively large resistance values used in the feedback network. This example implements the test circuit described in this interesting article by Analog Devices: https://t.co/xA548xt4BT

The undesired peaking observed in the frequency-domain closed-loop transfer function, and the ringing in the time-domain step response, depend on the resistor values chosen for r_fb and r_g. The ratio of these resistors must equal 1.0, for the desired low-frequency closed-loop non-inverting gain of 2.0. But if the actual value of each resistor is set to 499 Ohms, as recommended in the article, these problems are greatly reduced.

Note that the op-amp model used in this circuit was created using the Datasheet Model Builder tool, and is based on the corresponding Analog Devices Datasheet (Rev A). The common-mode input capacitance is not included in the model, so two capacitors were added externally in this circuit. In addition, note that the value of that capacitance is specified as 1 pF in the Datasheet, but each capacitor is set to 4.5 pF here. This value is based on the published SPICE model for this part, and was used to more closely match the SPICE simulation results shown in the article.

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Op-amp feedback resistor and stability

HaiNguyen
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HaiNguyen

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Description

This circuit shows the interaction effect between an op-amp's input capacitance and relatively large resistance values used in the feedback network. This example implements the test circuit described in this interesting article by Analog Devices: https://t.co/xA548xt4BTThe undesired peaking observed in the frequency-domain closed-loop transfer function, and the ringing in the time-domain step response, depend on the resistor values chosen for r_fb and r_g. The ratio of these resistors must equal 1.0, for the desired low-frequency closed-loop non-inverting gain of 2.0. But if the actual value of each resistor is set to 499 Ohms, as recommended in the article, these problems are greatly reduced.Note that the op-amp model used in this circuit was created using the Datasheet Model Builder tool, and is based on the corresponding Analog Devices Datasheet (Rev A). The common-mode input capacitance is not included in the model, so two capacitors were added externally in this circuit. In addition, note that the value of that capacitance is specified as 1 pF in the Datasheet, but each capacitor is set to 4.5 pF here. This value is based on the published SPICE model for this part, and was used to more closely match the SPICE simulation results shown in the article.

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Op-amp feedback resistor and stability

Mike Donnelly
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Mike Donnelly

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10 years 5 months

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Member of the PartQuest Explore Development Team. Focused on modeling and simulation of analog, mixed-signal and multi-discipline systems covering a broad range of applications, including power electronics, controls and mechatronic systems.

Description

This circuit shows the interaction effect between an op-amp's input capacitance and relatively large resistance values used in the feedback network. This example implements the test circuit described in this interesting article by Analog Devices: https://t.co/xA548xt4BTThe undesired peaking observed in the frequency-domain closed-loop transfer function, and the ringing in the time-domain step response, depend on the resistor values chosen for r_fb and r_g. The ratio of these resistors must equal 1.0, for the desired low-frequency closed-loop non-inverting gain of 2.0. But if the actual value of each resistor is set to 499 Ohms, as recommended in the article, these problems are greatly reduced.Note that the op-amp model used in this circuit was created using the Datasheet Model Builder tool, and is based on the corresponding Analog Devices Datasheet (Rev A). The common-mode input capacitance is not included in the model, so two capacitors were added externally in this circuit. In addition, note that the value of that capacitance is specified as 1 pF in the Datasheet, but each capacitor is set to 4.5 pF here. This value is based on the published SPICE model for this part, and was used to more closely match the SPICE simulation results shown in the article.

About text formats

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Copy of Op-amp feedback resistor and stability - on Fri, 06/19/2020 - 08:17

ton.pijpers44Designer232538

ton.pijpers44

Member for

Op-amp feedback resistor and stability

HaiNguyenDesigner65711

HaiNguyen

Member for

Op-amp feedback resistor and stability

Mike DonnellyDesigner19

Mike Donnelly

Member for

ton.pijpers44
Designer232538

HaiNguyen
Designer65711

Mike Donnelly
Designer19