If so, then the formula would look like:
Z = R || 1/jwC
= R || -jX
where X = -1/jwC
= (R * -jX) / (R - jX)
= (-jRX) * (R + jX) / (R^2 + X^2)
= (R*X^2 - jX*R^2)/(R^2 + X^2)
= RX(X - jR)/(R^2 + X^2)
= RX/(X + jR)
= [R/wC]/(1/wC + jR)
(feel free to check my math)
If the frequency is very low (i.e., 1/wC >> R), then the formula
can be estimated at:
Z = [R/wC]/(1/wC)
= R
Which would agree with the concept that capacitance has little
effect at low frequencies.
At high frequencies (i.e., 1/wC << R), then the formula can be estimated
at:
Z = [R/wC]/(jR)
= -j/wC
Again, this agrees with the idea that the capacitance dominates at
high frequencies.
Given an input capacitance and an input resistance, I believe
this configuration/formula would better match the measured
impedance. Comments?
Pat
> I suppose, R+1/j*w*c?
>
> Thanks,
>
> -Dima
> ============================
> Dima Smolyansky
> TDA Systems, Inc.
> 7465 SW Elmwood St.
> Portland, OR 97223
> (503) 977-3629
> (503) 245-5684
> dima@tdasystems.com
> http://www.tdasystems.com
>
>
> >
> > what is the input impedance of CMOS devices (for calculating the reflection
> > coff.)as a function of input capacitance ? how I calculate this impedance ?
> > what is the formula ?
> >
> > Best Regards
> > Shimon Turgeman
> > Applied Materials
> >
-- Pat Zabinski ph: 507-284-5936 Mayo Foundation fx: 507-284-9171 200 First Street SW zabinski.patrick@mayo.edu Rochester, MN 55905 www.mayo.edu/sppdg/sppdg_home_page.html
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