![]() You should simulate your stability in the feedback configuration you intend to use. Direction of iprobe does not matter for stb simulation. You can place the iprobe anywhere in the loop and it should give you the same results, unless by moving it you start disturbing other loops in the system. Yes, the stb results are reliable for small signal stability. Now, with your setup you can sweep the input voltage and test stability for the entire range you're interested in and you should not much worry about offset. Actually, that iprobe is implementing a modified version of the Middlebrook method for simulating stability. This is part of what the iprobe in cadence does. And that's exactly the reason why you simulate stability by breaking the loop in ac but keeping the loop closed for DC. It is not like simulating the amplifier open loop. There is a feedback which will not allow the opamp to rail. Given the virtual short at the inputs of the opamp, the output of the amplifier will settle at the 1.65V+/-Voff. So, if you keep your input at 1.65V DC, you can imagine that there is an additional voltage source in series with the 1.65V voltage source that accounts for the offset of the amplifier referred to the input. You have a setup where the amplifier is in a feedback configuration and as with any other feedback topology, it will try to achieve virtual short between the two inputs of the amplifier (to the extend allowed by your loop gain). My second question please, Does the STB result has good accuracy and can it be depended ?įirst, about your offset question. Such kind of simulation if I would perform by using the classical open loop setup it will not be accurate because the offset voltage also can change with the input voltage range. Such a property is very important for me when I want to simulate the DC gain over the entire range of the input common mode voltage. However from the STB analyses I can see it is closed loop feedback so I think there is no need for warring about the offset voltage compensation, My question here, when I measure the AC parameters from the open loop gain (the classical simulation setup) I have to be very careful to compensate for the input offset voltage, otherwise my setup can easily fail, After running the simulation I can get all the required parameters, The simulation setup is as I attached it below, as you can see that the circuit is provided only with DC, then I run the STB simulation and using the Iprobe as the instance. Some friends suggested me to use the stability analyses from cadence to get the AC parameters of my amplifier (DC gain, GBW, PM) ![]()
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December 2022
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