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OPA810: OPA810

c chow
Prodigy 20 points
Part Number: OPA810
Other Parts Discussed in Thread: TINA-TI

Tool/software:

I got your feedback on to implement negative capacitance using OP AMp. However, the biggest problem is on stability of your suggestion circuit.  I would like to get CFOA circuit that can do LT spice simulation model to run simulation. I hope to get the negative capacitance 1000pf - 500pf for my compensation. the frequency response range from 30hz-30Mhz, phase margin > 50degree, 

  • 0
    TI__Mastermind 24209 points

    Hello,

    While I cannot provide an LTSPICE simulation file, I can simulate in TINA-TI and Orcad PSPICE to help design your system.

    Do you have the load for your circuit output?

    Best,

    Alec

  • 0
    Prodigy 150 points

    Hello,

    I have no idea what kind of compensation you are trying to achieve, and why you need negative capacitance and not other means (if any)>

    However, generally I can advise that such negative capacitance emulator might create even more instability.

    1) If "C" (as per my schematic in the previous thread) is large enough, and the -C emulator is connected to a real capacitance (which by absolute value shall be more than negative) then the op-amp is at risk of oscillating close to the op-amp GBW frequency.

    2) If your op-amp is short of GBW, it will start to create some negative resistance together with negative capacitance closer to the loop GBW frequency. As you probably aware, negative impedance is a recipe for various kinds of instability. You might need now to compensate the negative admittance by connecting a resistor across the terminals of the "-C emulator".

    3) You might think that by adding a small resistor in series with C you will cure the problems. Not quite. You will eliminate issue (1) but at the same time aggravate issue (2).

    So all in all your negative capacitance thing is very "fiddly" and I am not sure if it is the right approach to fix your primary problem.

    Regards, Alex

  • 0
    TI__Expert 4236 points

    Can you share the circuit for me to analyze