Electrical filter circuits are tested by connecting to the filter inputs without the need to connect to the filter outputs or to disconnect the outputs from a load. A signal generator of known source resistance applies a.c. signals successively over a range of frequencies to the filter inputs, and a...http://www.google.com/patents/US6326793?utm_source=gb-gplus-sharePatent US6326793 - Method and apparatus for testing frequency-dependent electrical circuits
