Digital Processing in Tunneling Spectroscopy
  An alternative approach to detect very weak singularities on the characteristics of a tunnel diode is proposed in which the numerical differential filtering is applied directly to measured current versus voltage dependence instead of the modulation technique commonly used with this purpose. The gains and looses of the both approaches in the particular case of tunneling investigations of semiconductors under pressure are discussed. The corresponding circuitry and mathematical routines are presented. 
E.M. Dizhur, A.V. Fedorov