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Selecting inductor for bias-tee application - RF Cafe Forums
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Below are the old forum threads, including responses to the original posts.
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Post subject: Selecting inductor for bias-tee application
Posted: Mon Jun 26, 2006 12:03 pm
Fri Jun 23, 2006 11:12 am
I need to implement a bias-tee
in a 50 Ohm, 900 MHz circuit to extract a logic signal superimposed
on the RF signal. As a coupling capacitor is already present in the
existing circuit, I only need to add an inductor to tap the DC off the
composite signal. Two questions:
1. Should the inductor value
be set to render the DC tap high impedance at 900 MHz, say 500 Ohms
2. What are the guidelines for considering the inductor's
Self Resonant Frequency? I gather that this is the frequency beyond
which the inductor no longer behaves as an inductor due to parasitic
capacitance? In this 900 MHz application what would be the minimum safe
value for Self Resonant Frequency?
Post subject: Posted:
Mon Jun 26, 2006 3:56 pm
Joined: Mon Jun
27, 2005 2:02 pm
The answers are below your questions:
Should the inductor value be set to render the DC tap high impedance
at 900 MHz, say 500 Ohms or greater?
2. What are the guidelines for considering the inductor's Self Resonant
Frequency? I gather that this is the frequency beyond which the inductor
no longer behaves as an inductor due to parasitic capacitance? In this
900 MHz application what would be the minimum safe value for Self Resonant
Yes, the Self-Resonance frequency is
the frequency at which the parasitic capacitance form a resonance circuit
with the inductor. For 900MHz frequency I would choose 1.5GHz and higher
Post subject: Posted: Mon
Jun 26, 2006 6:40 pm
Joined: Fri Jun 23, 2006
Thanks very much for your prompt
and informative response.
Post subject: selecting inductor for bias-Tee applicationPosted:
Tue Jun 27, 2006 2:52 am
Joined: Fri Feb
17, 2006 12:07 pm
Location: London UK
of the inductor at the operating frequency should be at least ten times
the circuit impedance level.
Care also needs to be taken with
choice of bypass capacitor since this can also have resonant frequencies
due to internal inductance.
I have seen articles that give guidelines
on parameters, published in trade mags like RF & Microwaves, MWJ
Post subject: Posted: Tue
Jun 27, 2006 10:58 pm
Joined: Tue Mar 15,
2005 11:43 pm
following application note might be useful information on high power
device biasing consideration.
I hope it helps