Reducing AC impedance measurement errors caused by the DC voltage dependence of broadband high-voltage bias-tees

During the AC impedance characterization of devices, from the kHz-range up to the GHz-range, accuracy can be lost when a DC voltage is applied. Commercial high-voltage broadband bias-tees are often voltage-dependent, which can cause inaccuracies at low frequencies. A calibration technique with applied bias significantly improves the measurement accuracy.\ud Additionally, a bias-tee has been developed with a voltageindependent capacitor, suitable for DC voltages up to 500 V showing excellent performance up to several gigahertz. PIN diode limiters protect the measurement equipment from damage in case of a device breakdown.\u

On the Trade-Off Between Quality Factor and Tuning Ratio in Tunable High-Frequency Capacitors

A benchmark of tunable and switchable devices at microwave frequencies is presented on the basis of physical limitations to show their potential for reconfigurable cellular applications. Performance limitations are outlined for each given technology focusing on the quality factor (Q) and tuning ratio (eta) as figures of merit. The state of the art in terms of these figures of merit of several tunable and switchable technologies is visualized and discussed. If the performance of these criteria is not met, the application will not be feasible. The quality factor can typically be traded off for tuning ratio. The benchmark of tunable capacitor technologies shows that transistor-switched capacitors, varactor diodes, and ferroelectric varactors perform well at 2 GHz for tuning ratios below 3, with an advantage for GaAs varactor diodes. Planar microelectromechanical capacitive switches have the potential to outperform all other technologies at tuning ratios higher than 8. Capacitors based on tunable dielectrics have the highest miniaturization potential, whereas semiconductor devices benefit from the existing manufacturing infrastructure

Fast RF-CV characterization through high-speed 1-port S-parameter measurements

We present a novel method to measure the capacitance-voltage relation of an electronic device. The approach is accurate, very fast, and cost-effective compared to the existing off-the-shelf solutions. Capacitances are determined using a single-frequency 1-port S-parameter setup constructed from discrete components. We introduce a new way to correct for non-linearities of the used components, which greatly increases the accuracy with which the phase and magnitude of the reflected signal is measured. The measurement technique is validated on an RF-MEMS capacitive switch and a BST tunable capacitor. Complete capacitance-voltage curves are measured in less than a millisecond, with a measurement accuracy well below 1%.\ud \u

Reversing quantum trajectories with analog feedback

We demonstrate the active suppression of transmon qubit dephasing induced by dispersive measurement, using parametric amplification and analog feedback. By real-time processing of the homodyne record, the feedback controller reverts the stochastic quantum phase kick imparted by the measurement on the qubit. The feedback operation matches a model of quantum trajectories with measurement efficiency $\tilde{\eta} \approx 0.5$, consistent with the result obtained by postselection. We overcome the bandwidth limitations of the amplification chain by numerically optimizing the signal processing in the feedback loop and provide a theoretical model explaining the optimization result.Comment: 5 pages, 4 figures, and Supplementary Information (7 figures

Separation of intrinsic dielectric and resistive electrode losses in ferroelectric capacitors at radio frequencies

To analyze the intrinsic dielectric performance of planar high-density capacitors at radio frequencies (RF), the dielectric losses need to be distinguished from the resistive electrode losses. The resistive losses of the electrodes at RF are de-embedded employing a linear regression procedure with partial compensation for distributed effects. We use tunable ferroelectric capacitors with a barium strontium titanate (BST) dielectric with an inner diameter d ≥ 8 μm on a silicon substrate. The de-embedding of the electrode losses has been successfully performed utilizing 1-Port RF measurement data from of an Advantest R3767CG vector network analyzer (VNA) in the frequency range of 10 MHz – 8 GHz

Th1 Lymphokine Production Profiles of Nickel-Specific CD4+ T-Lymphocyte Clones from Nickel Contact Allergic and Non-Allergic Individuals

Panels of nickel-specific T-lymphocyte clones (TLC) were prepared from nickel-allergic and non-allergic donors. TLC from both panels showed similar levels of expression of TCRα/β, CD4, CD2, CD25, and CD29 and recognized nickel in association with class II HLA molecules with restriction determinants in HLA-DR, HLA-DP, and HLA-DQ. The lymphokine secretion was analyzed in TLC from both panels upon antigen-specific or non-specific stimulation and was compared with the secretion profiles of representants of pre-established human atopen-specific Th1 and Th2 cells. Nickel-specific TLC from both panels showed a lymphokine secretion pattern similar to the atopen-specific Th1 cells, although there was some variation from clone to clone. Most TLC secreted substantial amounts of IFN-γ, IL-2, TNF-α and GM-CSF, but little or no IL-4 and IL-5. The variation observed mainly concerned IL-2 secretion that could be low or absent in some of the TLC. The general secretion pattern did not change upon different modes of stimulation, including activation via CD3, CD2, or CD28. Because nickel-specific TLC from allergic and non-allergic individuals show a similar Th1 secretion pattern, the present results give no evidence that aberrant lymphokine secretion by CD4+ T cells determines the contact allergic state, as was found for atopic allergy in a previous study