Integrated spiral inductors

[e.Horus]

Hello all,

Urgent question:
Given a grounded (1-port) integrated spiral inductor on Si substrate:

1. Which is the recommended connection: connecting the RF node to the outer turn of the inductor and ground the inner turn, or the RF node to the inner turn and ground the outer turn?

2. Which connection resuolts in higher Q?

3. Which connection results in higher resonance frequency (lower capacitance)?

∞ Thanks for your help
Cheers

 

[A.Anand Srinivasan]

when you are talking about a spiral inductor it means that its inductance doesn't change just because you interchange the terminal so how do you expect the resonant frequency.... the selection of connection point of RF node depends on which makes lesser disturbance...
i think connecting it to the inner turn is better in terms of emi of the source....

 

[e.Horus]

The inductance may not change, but I believe that the resonance frquency changes as the equivalent capacitance is not the same on each port. The question is which will yield lower parastic cap and higher Q?!

 

[A.Anand Srinivasan]

how do you say the equivalent capacitance will change in each port????

 

[e.Horus]

If you consider a simple 2-port PI model, the capaciatcnes on the sides of the PI are generaly different from each other due to the distributed nature of the spiral. Depending on which port you ground, you will end up with a different resonance frequency. The question which capacitance is higher?

Cheers

 

[A.Anand Srinivasan]

i thought that since the same signal is passing through the coil the capacitance would be low because the change in voltage across nearby coils would be too low for the capacitance to take action....