Why too low frequency of Negative capacitor using opamp?

[zhangm79]

hi, all. I need realize negative capacitor from 80MHz to 108 MHz by NIC using opamp, the opamp 3-dB bandwidth is 150MHz. But the negative cap can be got under 1.5MHz.
Anyone can help to explain why?

 

[zhangm79]

anyone can help?

 

[kspalla]

Can you share the design?

 

[FvM]

I doubt, that the loop bandwidth will be 150 MHz, I guess, it's rather the unity gain bandwidth respectively GBW product.
In any case, a much higher OP bandwidth would be necessary to generate almost capacitive behaviour.
Circuit stability is another topic.

 

[zhangm79]

Thanks a lot. I change to LMH6703, and simulated by ADS, achieve good negative capacitor in FM band. I would upload the design after testing