  Transition-edge sensors (TESs) are used as very sensitive thermometers in
microcalorimeters aimed at detection of different wavelengths. In particular,
for soft X-ray astrophysics, science goals require very high resolution
microcalorimeters which can be achieved with TESs coupled to suitable
absorbers. For many applications there is also need for a high number of pixels
which typically requires multiplexing in the readout stage. Frequency Domain
Multiplexing (FDM) is a common scheme and is the baseline proposed for the
ATHENA mission. FDM requires biasing the TES in AC at MHz frequencies. Recently
there has been reported degradation in performances under AC with respect to DC
bias. In order to assess the performances of TESs to be used with FDM, it is
thus of great interest to compare the performances of the same device both
under AC and DC bias. This requires two different measurement setups with
different processes for making the characterization. We report in this work the
preliminary results of a single pixel characterization performed on a TiAu TES
under AC and afterwards under DC bias in different facilities. Extraction of
dynamical parameters and noise performances are compared in both cases as a
first stage for further AC/DC comparison of these devices.
