Induction Trace Width of FR4

[PaulHolland]

Hi, I made a Amplifier and used PCB tracks as inductors I used 5nH/inch for 240 mill width tracks and 7.6nH/inch for 120 mill tracks. Can anyone conferm that these values are correct ??..

Thanks, Paul.

 

[House_Cat]

The self inductance of a trace is a function of the distance to the reference plane(s) or other board structures. Is this a microstrip or a stripline? What is the distance to the reference plane or trace?

 

[biff44]

No, nobody can tell if you are correct. That is because there is insufficient info provided.

A length of line on a PCB is a transmission line. If it is wide, it looks like a low impedance transmission line. If it is narrow, it looks like a high impedance transmission line.

In certain VERY NARROWBAND cases, a high impedance transmission line can look like a series inductor. Similarly, a low impedance transmission line can look like a shunt capacitor.

240 mils wide does NOT sound very narrow! So right off the bat, it will make a relatively poor inductor. The real key, though, is how long the transmission line is. If your line that is trying to look like an inductor is any longer than say 0.1λ, then all bets are off.

So lay the frequency and bandwidth you are looking for on us, and we will tell you if you are anywhere close. Also, tell us exactly what you are doing to both ends of the "line".

 

[PaulHolland]

Hi. The microstrip line is made on FR4 (Er 4.5) 1mill thick coper with tracks on top and GND plane on bottom. Its part of an impedance matching netwrk for a transisor with 3 capacitors on the line. beginning, middle (some what) and end. Freqyency range is 88-108 MHz. Circuit was first designed and tested with normal coils and worked perfect (wideband design) to lower cost we attempted to change the coils into PCB tracks. Total line length is 7 inch

regards,

Paul.

 

[Grig]

Hi

I have experimented with inductance of pcb traces using field solver.
The trace inductance on FR4 is function of trace width, thicknes and height over ground. And the location of the trace on the ground. Also I seen that inductance value may be (~20%) more, if the ground is finite in comparison with infinite ground (which is typical default for field solver).
I thinck You should take in to account factors above to design pcb inductance value You need.

Regards