Electronic – impedance ‘masking’ and how it is related to impedance ‘matching’

impedance-matchingpower electronics

While reading ECSS-E-ST-20C Standard, I have encountered with a concept named 'impedance mask'. However, I could not find any detailed definition or explanation related to it.

In the corresponding article, it is said that :

"At the point of regulation, the impedance mask of a fully regulated bus, operating with one source shall be below the impedance mask shown in Figure 5‐1."

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I would like to know what impedance masking is and how it is related to -if so- impedance matching.

Best Answer

I think it's talking about a DC power distribution bus and basically it's saying that the source of the regulated voltage on that bus must have a very low output impedance. If it didn't have a low output impedance it wouldn't regulate very well.

The term "mask" just refers to the allowable "top-limit" of impedance that is acceptable and, as far as I can tell has no bearing on such concepts as impedance matching.

So, take the example of a 5V bus capable of putting out 100 watts. At low frequencies (0.01 Hz or less) the output impedance can be calculated from the graph as: -

0.002 x voltage\$^2\$ / power = 0.4 milli ohms

OK I found ECSS-E-ST-20C and it says (regarding this test): -

NOTE 2 Rationale for the impedance mask: It translates requirement 5.7.2i.1 of 1 % voltage change for 50 % load change in a domain of regulation up to 10 kHz bandwidth. In DC the integrator in the control loop is designed to ensure no static error, in higher frequency, between 10 kHz and 100 kHz it is likely that the inductance effect of the components and connections are seen and the impedance rise not always making feasible to respect the ideal impedance mask.

This proves to me it is about power sources feeding a power bus.

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