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I am simulating an RC integrator using an ideal opamp. I model the opamp as two different models (one with vcvs and the other with vccs) as shown in the below two cases. When I ran the ac simulation, only the one with vcvs worked fine. I don't understand why the vccs one didn't work. Could you please help me out?

Opamp with VCVS:

enter image description here

Opamp with VCCS:

enter image description here

AC Analysis Result: enter image description here

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Simply put, when you use a VCCS model, you are assuming a transconductance amplifier (like a 5T-OTA) which inherently has a large (ideally infinity) output resistance. Under such conditions, the current through C is forced by the ideal current source, driving the input difference and the output current to zero. In other words, you have built a very lossy integrator! Generally, lower output impedances are preferred for continuous-time integrators using OpAmps, whereas a large output impedance can be used to design a discrete-time (switched-capacitor) integrator using a transconductance amplifier.

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  • \$\begingroup\$ Thank you very much for your reply. I found out that there was a connection error in the circuit. After I fixed it, the two matched up. \$\endgroup\$
    – Kenlucius
    Commented Jul 13 at 9:04

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