When I look at various capacitor data sheets, they often have a insertion loss vs freq plot (in dB). If I want to find the best IC power supply decoupling cap, shall I look for the one with the minimum insertion loss?
If so, it is usually the smallest value (e.g. a few pF) has the lowest insertion loss at the highest freq, but this is not enough for poweer decoupling purpose, right?
so ,I am at a loss with this "insertion loss" for the cap thing. Please help ....
If so, it is usually the smallest value (e.g. a few pF) has the lowest insertion loss at the highest freq, but this is not enough for poweer decoupling purpose, right?
so ,I am at a loss with this "insertion loss" for the cap thing. Please help ....
Really? I didn't know that.
I thought that there should be as little loss as possible for the power decoupling cap, so the noise will flow through the cap much "easier".
I guess I am missing something here right? Please help. Thanks.
I thought that there should be as little loss as possible for the power decoupling cap, so the noise will flow through the cap much "easier".
I guess I am missing something here right? Please help. Thanks.
The purpose of a decoupling cap (on a power supply) is to provide a return path to ground at the lowest possible value, over as wide a range as possible.
Of course.....it depends on capacitance and frequency, so no one cap works in all situations.
Someitmes, it is desirable for a cap to have a slightly higher than normal series resistance. Some regulaotors have peaking problems if the series resistance is zero ohms.
Insetion loss is used to describe the characteristics of a L-C filter, in terms of the signal that is absorbed by the filter.
Two different cases.
Jocko
Of course.....it depends on capacitance and frequency, so no one cap works in all situations.
Someitmes, it is desirable for a cap to have a slightly higher than normal series resistance. Some regulaotors have peaking problems if the series resistance is zero ohms.
Insetion loss is used to describe the characteristics of a L-C filter, in terms of the signal that is absorbed by the filter.
Two different cases.
Jocko
pop11 said:
A cheap capacitor with 10% insertion loss but 100 x the value of a capacitor
with 1% loss is far better for basic power supply decoupling duties.
If high frequency loss is an issue add higher quality bypass capacitors.
🙂 sreten.
pop11 said:
Insertion loss refers to the amount the signal is attenuated in a RF circuit when the cap is used as a series pass element. This is generally stated in "dB insertion loss @ X mHz". Most of the time this will be spec-ed at 50 or 75 ohms.
Not an issue for PS bypass use.
If for some reason known only to you, you think this is a big deal choose a cap with lowest loss at the frequency where the electrolitics you are bypassing impedance starts to rise.
Later BZ
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