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Transistor Modeling and Simulation
Published in Abdullah Eroglu, Introduction to RF Power Amplifier Design and Simulation, 2018
In practice, the device parasitics are measured using a test fixture that interfaces the device with the equipment. The DUT can be characterized accurately by removing the test fixture characteristics from the measured results. VNA is commonly used as the measurement equipment to characterize the RF and microwave components. To characterize the device parasitics, the S parameters for the DUT must first be de-embedded from the total measured S parameters. The input and output sides of the test fixture also have some reactance caused by the coaxial-to-CPW transition.
EMI Measurements, Control Requirements, and Test Methods
Published in David A. Weston, Electromagnetic Compatibility, 2017
The current probe should be calibrated in a test fixture that raises the body of the probe from contact with the return (ground plane) of the test fixture. It is important in measurements to ensure that the body of the current probe is not in contact with the ground plane and if possible is at the same height above it as used in the test fixture.
Modulation for Short-Reach Access Optical Transmission
Published in Le Nguyen Binh, Optical Modulation, 2017
Typically, engineers design test fixtures with a controlled impedance environment so the fixture effects can be minimized, but it is impossible to completely eliminate skin effect series trace loss, dielectric shunt loss and inductive or capacitive impedance discontinuities of the fixture channel. Test fixture deficiencies cause signal loss and reflection with increased effects at higher frequencies. A few different approaches used to remove the test fixture effects from the measurement include direct measurement (pre-measurement process) and de-embedding (post-measurement processing). Direct measurement uses specialized calibration standards that are inserted into the test fixture and measured. De-embedding uses models of the test fixture [17] and mathematically removes the fixture characteristics from the overall measurement. De-embedding methods require that an accurate characterization model of the fixture be obtained first. Examples of de-embedding methods include “simulation-based” and “calibration-based.” The simulation-based method simulates the waveform before the fixture is fabricated. The calibration-based method is used to eliminate fixture effect after the fixture is available [18] for use during the measurement process. Simulation modeling is enabled for PAM-4 designs in the arbitrary waveform generators (AWG). Simulations help to provide evaluation and performance prediction of a specific portion of a link or a complete end-to-end link design. Complex behaviors of NRZ transmitter and receiver signals can be modeled using the algorithmic modeling interface (AMI) standard. AMI is a behavioral model first defined in the input/output (IO) buffer information (IBIS) 5.0 specification, and provides both passive channel characteristics and SerDes functionalities [17]. The current AMI standard supports NRZ signaling, assuming the Tx signal has two levels and the receiver slicer reference is at 0V. The simulation flow for PAM-4 link can be seen in Figure 9.14 with a four-level input waveform and output waveform with clock data recovery (CDR) times and eye diagram with delay shift dependent on the modulated amplitude in Figure 9.15.
Control rod position measurement by two-electrode capacitance sensor in nuclear heating reactor
Published in Journal of Nuclear Science and Technology, 2019
Guang Hu, Benke Qin, Qianfeng Liu, Hanliang Bo
There are several things to notice above. Connecting a DUT to the measurement terminals of the auto-balancing bridge instrument requires a test fixture or test cables. The selection of the appropriate test fixtures and cables, as well as the techniques for obtaining the optimum DUT connection configuration, are important for maximizing the total measurement accuracy. The four-terminal configuration can reduce the effects of lead impedances and contact resistances because the signal current path and the voltage sensing leads are independent. Typical factors for measurement discrepancies in impedance measurements are listed as follows: variance in residual parameter value; a difference in contact condition; a difference in open/short compensation conditions; electromagnetic coupling with a conductor near the DUT; and variance in environmental temperature. Stray capacitance between the contact electrodes of a test fixture is a significant error factor compared to the residual impedance. To make interconnections with the DUT, use a shielded four-terminal configuration. Proper guarding techniques and the open/short compensation can minimize the effects of stray capacitance.