IRIS Pol. Torinohttps://iris.polito.itIl sistema di repository digitale IRIS acquisisce, archivia, indicizza, conserva e rende accessibili prodotti digitali della ricerca.Wed, 13 Nov 2019 14:50:51 GMT2019-11-13T14:50:51Z1041A New Approach to Characterize Complex ICs in Terms of Scattering Parametershttp://hdl.handle.net/11583/2692767Titolo: A New Approach to Characterize Complex ICs in Terms of Scattering Parameters
Abstract: The macro-models used in chip-level EMC analysis usually comprise equivalent circuits whose
parameters are derived from the results of scattering parameter measurements. The constant
increment of IC complexity along with the increment of the pin number has made this job
difficult to accomplish, because of the numerous measurements to carry out and the propagation
of related errors. Aiming to address this issue, this paper explores the possibility to obtain the
scattering parameter matrix of an N-port system from measurements carried out with an m-port
vector network analyzer, with the remaining N-m ports left open or loaded with a set of known
impedances. According to the definition of scattering parameters, the measurement must be
carried out with the ports loaded by their respective characteristic impedance (usually 50Ω ),
which makes such measurements time-consuming, especially with devices featuring many
ports. This is mostly because the N-m port not connected to the VNA must be matched during
the measurement process.
This paper presents a method that allows one to obtain the scattering matrix of an N-port device,
using the S-par measurements carried out with the N-m ports not connected to the VNA, left
open. The proposed technique requires ( ) set of measurements (Fig. 1), but there is no need
to match with the reference impedances the port of DUT that are not connected to the VNA
during the measurement process. To this purpose, three different methods suitable to derive the
scattering parameters with the remaining N-m ports mismatched are available in literature. All
these algorithms are based on two-step matrix transformation: the first step, starting from
mismatched measured parameters, builds a set of partial matrices (S^p) containing the
information related to the auxiliary load, while the second one reconstructs the true S parameter
matrix from the partial matrices obtained in the first step. The great advantage of this approach
is that the port not connected to the VNA can be left open. Unfortunately, this condition could
be problematic because the parasitic elements loading the port not connected to the VNA, could
affect the elements of the extracted matrix, especially at high frequency. The use of these
techniques significantly reduces the number of steps needed to extract the final matrix.
Aiming to check the proposed method, a three port IC was characterized using a 2-port VNA.
At first, the scattering parameters resulting from the proposed procedure and those obtained
using the definition of scattering parameters do not match in some frequency ranges. The
mathematical analysis carried out afterwards pointed out that the observed errors deal with the
conditioning number of the matrix to be inverted in the second step.
Furthermore, the more the reflection coefficient magnitude of the auxiliary loads is close to one,
the higher is the probability to obtain a high condition number, increasing the error of the
reconstructed matrix. Therefore, in order to avoid the matrix inversion in ill conditioned point,
the Newton’s method was chosen as the optimal solution and its goodness was checked by
repeating such a test on the above-mentioned circuit, as shown in Fig. 2.
Sun, 01 Jan 2017 00:00:00 GMThttp://hdl.handle.net/11583/26927672017-01-01T00:00:00ZInvestigation on the Switching Waveforms of GaN Power Devices to Gate Current Profileshttp://hdl.handle.net/11583/2756652Titolo: Investigation on the Switching Waveforms of GaN Power Devices to Gate Current Profiles
Abstract: The extended use of Gallium Nitride (GaN) transistors in power applications, such as automotive, industrial and power distribution, leads practitioners and researchers to a review of the classical driving techniques, to meet the different characteristics of such devices compared to traditional ones, such as MOS and IGBT. In particular, the smaller intrinsic capacitances of GaN transistors allows faster switching transitions, thus decreasing the power dissipation during commutations. On the other hand, the higher slope of the switching waveforms drives high frequency resonant circuit that, using slower devices, would not be excited.
This paper proposes a technique to obtain an optimal pair of non-oscillating switching waveforms, which exploits time-varying resistances in the power loop. A gate charge driving technique, based on the modulation of the gate current, is exploited for shaping the optimal waveforms by means of the power transistor itself. A simulation analysis was carried out considering two different driving waveforms and studying the sensitivity of ringing as a function of their significant parameters. Such analysis highlights that the optimal switching waveforms can be obtained by means of several driving shapes. Finally, a comparison with the RC snubbered circuit, in terms of efficiency and ringing, is reported to highlight the advantages of the proposed technique.
Tue, 01 Jan 2019 00:00:00 GMThttp://hdl.handle.net/11583/27566522019-01-01T00:00:00ZNovel Solutions to Reduce the EM Emissions of Power Switching Circuitshttp://hdl.handle.net/11583/2756492Titolo: Novel Solutions to Reduce the EM Emissions of Power Switching Circuits
Abstract: The introduction of wide bandgap (WBG) devices in power modules has led to increased system efficiency, since those transistor switch faster. This, however, results also in increased electromagnetic emissions. In the last years, the research activity has tried to develop software techniques in order to address such an issue. Among them, the spread spectrum technique can be used, but this approach does not reduce the EM emission energy.
In order to reduce the electromagnetic interference (EMI) energy, a first approach, that can be used whenever there are a pair of nodes switching opposite, consist in aligning the transition edges, reducing the common mode emissions significantly.
However this approach is not sufficient, since the waveform edges are not perfectly equal and opposite, since the rising and falling time differ and some ringing can be present. To address this issue, recent investigations have shown that the switching transistors can be driven so that they behave as switches and as snubbers, simultaneously.
Tue, 01 Jan 2019 00:00:00 GMThttp://hdl.handle.net/11583/27564922019-01-01T00:00:00ZA Criterion for an Optimal Switching of Power Transistorshttp://hdl.handle.net/11583/2756493Titolo: A Criterion for an Optimal Switching of Power Transistors
Abstract: Power converters, especially those exploiting fast-switching devices, suffer from ringing, which worsens efficiency, EMI performance and increases the stress of components. Traditional approaches, such as RC snubber and series gate resistance, only partially mitigate the problem, whereas, active gate driver implies sub-optimal switching waveforms.
This paper presents a new criterion for controlling the turn-on and the turn-off of a power transistor using a three-levels current driver, which results in optimal switching waveforms.
The method shows better performance in terms of efficiency and transient slopes compared to traditional approaches.
Tue, 01 Jan 2019 00:00:00 GMThttp://hdl.handle.net/11583/27564932019-01-01T00:00:00Z