[SOLVED] how to design the design inductor for LC-tank oscillator.

[palmeiras]

Hello Guys,
I’m trying to design the inductor for the basic LC-tank oscillator. I need to specify all parameters of the inductor (width, turns, Skew, inner radius, and others), and after that, draw the layout of the inductor. Could you, please, give some hints or basic step-by-step process of designing the inductor? I’m not sure how I should choose these inductor parameters in order to achieve my inductance (for instance, 5 nH).

Any help will be great.

Thank you very much,

 

[saro_k_82]

SRF needs to be atleast thrice that of your maximum operating frequency. Q of the inductor must be maximized, but in reality close to 1/2 of the Q of the capacitor bank should do fine. When these two are satisfied, the inner radius, turns etc., impact the silicon area, which can be chosen to fit your floor-plan.

 

[palmeiras]

Hello Saro! Thanks for your reply.
1) SRF stands for Self resonance frequency? How can I define it to be at twice my maximum operation frequency?
2) Do you know the equation that relates inner radius, number of turns, and so on, with the inductance?
Thank you,

 

[saro_k_82]

It is easy to obtain these parameters through ac simulation (if it is not provided by the tool directly). Pass ac current in to the inductor and plot the ac response of voltage. Make sure that the center tap is biased as it would be in the design. SRF can be observed directly as the point of maxima. Q is the ratio of the imaginary part to the real part (at the frequency of interest). Higher number of turns provides low area, more inductance at higher Q, but lower SRF. So you can start with a design that occupies low area and see if it satisfies your design criteria.

 

[palmeiras]

What is the maximum value (estimation) of Q I can achieve by integrated inductors? For high-values and for inductance around few nano henry, what is the area required?
100 x 100, 200 x 200.. 300x 300... a very rough estimate?

Thanks!

 

[saro_k_82]

I dont know about max Q values obtainable within the die. Both the area and Q are heavy functions of the operating frequency. The typical Q values for frequencies around 15GHz is 15 and the area would be 150 x 150 (Single turn). As frequency decreases area increases (if number of turns is the same) and Q increases.