  Retarding field energy analyzers and Langmuir probes are routinely used to
obtain ion and electron energy distribution functions (IEDF, EEDF). These
typically require knowledge of the first and second derivatives of the I-V
characteristics, both of which can be obtained in various ways. This poses
challenges inherent to differentiating noisy signals, a frequent problem with
electric-probe plasma diagnostics. A brief review of commonly used analog and
numerical filtering and differentiation techniques is presented, together with
their application on experimental data collected in a radio-frequency plasma.
The application of each method is detailed with regards to the obtained IEDF
and EEDF, the deduced plasma parameters, dynamic range, energy resolution and
signal distortion.
