Hi,

I have saw people some paper mentioned that the capacitance value of a varactor (NMOS in accumulation mode) can varies with frequency, can anybody give an explanation why?

Thanks,

Hi Raj

Thanks for your reply. Actually, that was what I thought. However, please refer to the following paper and in Fig 3 (the plot of measured AMOS varactor at different frequency), I found it's non-monotonic. that puzzled me.

Hi Raj,

Thanks for remind for the publication.
When you looked at the figure 3b. Cap value is monotonic on bias voltage. However, for the same bias value, cap value is not monotonic on frequency, for example, when vbias=1v, it has C(55GHz)>C(5GHz)>C(1MHz)>C(20GHz).
If considering charge travel time, I would think that the higher the frequency, the smaller cap it will have, is that correct?

Thanks,

Norman