Thesis (MScEng (Electrical and Electronic Engineering))--Stellenbosch University, 2008. / This study investigates high frequency probes through good metrology and computation software such as CST. A factor that can strongly influence the accuracy of measurements, is common mode (CM) current. Therefore, the main focus of this project was the CM current on the outside of an SMA, flanged, probe used for measuring material properties. In the course of the investigation, a clamp-on CM current probe (CP) was calibrated using a CST model and good measurements. This calibration data indicated that the CP was invasive on the measurement setup and could not deliver the accuracy required for the CM current measurement. In light of this, a second method was implemented where the material probe was placed within a cylindrical shield. A cavity was formed between the probe and the walls of the shield in which the electric fields could be simulated and measured. These field measurements allowed measurements to be conducted in both the time- (TD) and frequency-domain (FD). For the TD measurements, a sampling oscilloscope was used. As the basic principle of a sampling oscilloscope differs from its real-time counterpart, this principle, as well as the systematic errors associated with these devices, was explored. The results of the final measurements indicated that the TD results were within an acceptable range of both the FD results, measured on the VNA, and the results predicted by CST. This study shows that CST can be used to simulate complex measurement setups and deliver reliable results in cases where an accurate measurement cannot be guaranteed.

Signal-integrity degradation from such factors as supply and substrate noise and cross talk between interconnects restricts the performance advances in Very Large Scale Integration (VLSI). To avoid this and to keep the signal-integrity, accurate measurements of the on-chip signal must be performed to get an insight in how the physical phenomenon affects the signals. High-speed digital signals can be taken off chip, through buffers that add delay. Propagating a signal through buffers restores the signal, which can be good if only information is wanted. But if the waveform is of importance, or if an analog signal should be measured the restoration is unwanted. Analog buffers can be used but they are limited to some hundred MHz. Even if the high-speed signal is taken off chip, the bandwidth of on-chip signals is getting very high, making the use of an external oscilloscope impossible for reliable measurement. Therefore other alternatives must be used. In this work, an on-chip measuring circuit is designed, which makes use of the principle of a sampling oscilloscope. Only one sample is taken each period, resulting in an output frequency much lower than the input frequency. A slower signal is easier to take off-chip and it can easily be processed with an ordinary oscilloscope.

<p>Signal-integrity degradation from such factors as supply and substrate noise and cross talk between interconnects restricts the performance advances in Very Large Scale Integration (VLSI). To avoid this and to keep the signal-integrity, accurate measurements of the on-chip signal must be performed to get an insight in how the physical phenomenon affects the signals. </p><p>High-speed digital signals can be taken off chip, through buffers that add delay. Propagating a signal through buffers restores the signal, which can be good if only information is wanted. But if the waveform is of importance, or if an analog signal should be measured the restoration is unwanted. Analog buffers can be used but they are limited to some hundred MHz. Even if the high-speed signal is taken off chip, the bandwidth of on-chip signals is getting very high, making the use of an external oscilloscope impossible for reliable measurement. Therefore other alternatives must be used. </p><p>In this work, an on-chip measuring circuit is designed, which makes use of the principle of a sampling oscilloscope. Only one sample is taken each period, resulting in an output frequency much lower than the input frequency. A slower signal is easier to take off-chip and it can easily be processed with an ordinary oscilloscope.</p>