  Continuous-wave electrically detected magnetic resonance (cw-EDMR or just
EDMR) and its variants are powerful tools to investigate spin-dependent
processes in materials and devices. The use of quadrature detection improves
the quality and selectivity of EDMR analysis by allowing, for example, the
separation of individual resonant spin lines. Here we propose an equivalent
circuit model in order to better understand the EDMR quadrature signal in a
variety of different situations. The model considers not just the electrical
response of the sample but of cables and measuring circuit and its influence on
the resulting spectral lines. Recent EDMR spectra from Alq3 based OLEDs, as
well as from a-Si:H reported in the literature, were successfully described by
the model. Moreover, the model allows the implementation of a fitting routine
that can be easily used to determine accurate values of crucial parameters such
as g-factor and linewidth of the resonant lines.
