(Q) What do the part numbers mean?

(A) In general the part numbers can be explained as follows:

(Q) What is the difference between a medical version, and the standard version of a filter?

(A) For medical applications, there is a requirement to keep leakage current (current flowing to earth) to an absolute minimum. This is mostly achieved by either removing the Y capacitors (connected between phase and earth), but this can lead to a lower performance at higher frequencies (above several MHz). Capacitors of very small values (pF) can be utilised to gain a better performance whilst minimising leakage current.

(Q) What's the difference between common mode & differential mode noise?

(A) Common mode (or Asymetrical Mode) is any noise that travels between the earth and phases. Differential Mode (or Symmetrical Noise) is noise that propagates between phases.

(Q) Why are there 4 curves on our insertion loss plots?

(A) On Schaffner insertion loss plots we show the insertion loss to signals based on a 50/50 system and a 0.1/100, 100/0.1 system.

What this means is we show the performance of the filter in an ideal world (50/50) and the insertion loss in a worst-case scenario (0.1/100, 100/0.1). The actual performance of the filter is very dependant upon the impedance of the noise source, but it usually falls somewhere between the worst case and ideal case.

 

(Q) How do I select the correct filter for my application?

(A) Unfortunately there is no simple way to recommend a filter for an application. A starting point is to determine what are the dominant noise sources within a system and try and select a filter that is suitable. When a filter has been chosen it is essential to test the unit to see how it performs.