Project C+ Solved

The circuit described in the April 2004 edition of Elektor Electronics certainly gave rise to a lot of head scratching and raised eyebrows when it was shown to produce an output pulse ahead of the input pulse. Is it possible that such a simple circuit can turn the principle of causality on its head? Read on…The idea for this article began when a student asked me if it was possible to build a filter that produced a ’negative group delay’. A quick trawl of the Internet (Google: ‘negative group delay’) soon gave some interesting hits. In particular Professor Kitano in Japan had published just such a circuit that apparently exhibits a negative group delay [1]. With kind permission from him we were able to use his ideas and circuit (slightly modified) in last month’s article. So much for the background, now on to the details...