Picking bias tee values

[aloishis89]

I'm working on a design with an amplifier, the PSA4-5043+. I need to make a bias tee as the schematic shows: https://www.minicircuits.com/pcb/WTB-653+_P02.pdf. I think I understand how a bias tee works, but I'm not sure how to calculate the values of L and C. My design is 50 ohms and operates from 470-700 MHz. I don't have a copy of ANSYS or other expensive simulation software, so is there a free software package I can use or an equation I can calculate?

 

[jiripolivka]

To use the PSA-4-5043+, you need to use a L the reactance of which is much larger than 50 Oms at the lowest operating frequency. The capacitor reactance should be much smaller than 50 Ohms at the lowest operating frequency.

If you look on the evaluation board details of Minicircuits, they indicate capacitor and inductor values.

 

[aloishis89]

I could be totally blind, but I don't see any values for L and C. There are a couple cap values, and they reference another part they make that is an integrated bias tee (tcbt-14+) but I don't see where the suggested values for L and C are. I don't want to use the TCBT-14+ because it's $9.

 

[mtwieg]

Well naturally they don't tell you their component values. If they did then you'd never buy their components.

A good bias T has a very low loss capacitor (like NP0 or even ATC caps), and a high Q inductor with low self capacitance. For broad bandwidths and high frequencies, the inductor is generally the tough part, but for your frequency range you should be okay will small ferrite chokes. A couple hundred nanohenries should be enough, just make sure the self resonant frequency is not in or below your operating frequency range.

 

[vfone]

Inside of the bias tee is an inductor L and a capacitor C.
As was stated you can make your own bias tee using an inductor L with reactance at working frequency about 10x bigger than 50 ohms (> 500 ohms), and a DC block capacitor. For wider bandwidths (up to microwaves) the inductors have various shapes.