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  1. #1
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    "Ideal" differential amplifier in SPICE

    Hello,

    I am working on a project for a course where I am required to design a differential OTA and implement the amplifier's feedback using switched capacitors.

    I would like to design the switched capacitor feedback network first, while i work out some kinks in my differential OTA, and thus would like to implement the feedback with an "ideal differential amplifier".

    Could not simply create this device with two VCVS (voltage controlled voltage source), are there any downsides to this I am not considering? I would expect the VCVS must be setup in such a way that they only amplify differential signals, and choose input and output common mode voltages such that they are close to the actual OTA. Am I off base here?

    Thanks.

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  2. #2
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    Re: "Ideal" differential amplifier in SPICE

    With ideal source don't care about common mode voltage. Common mode DC is normally used to set operating point for input/output transistors, without devices it will increase the complexity. If you are curious about DC capacitor voltages, obviously it is not a problem.
    The only drawback I see is the missing non-linearity from the system, which usually OTA's worst property, and hard to model in VCVS.
    And don't leave OTA's output load capacitance and source resistance from your model, they can screw your switched circuit design if you forget to consider.
    "Try SCE to AUX." /John Aaron/



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