Agilent Measurement Journal - Issue 3 - 2007 - (Page 48)

Measuring high-frequency current phase The thin-ﬁlm probe was used to measure the magnetic ﬁeld distribution over the pins of an automotive microcontroller. The microcontroller was in a QFP 100-pin package with closelyspaced pins. Measurements were made at 96 MHz, the second harmonic of the 48 MHz clock. Traditionally, phase is measured using an oscilloscope, where signals are measured in the time domain relative to a known signal (such as the microcontroller clock) and then converted to the frequency domain. A side effect of making the probe small is a decrease in sensitivity. For this reason, the traditional broadband phase extraction method is not effective for the thin-ﬁlm probe. To overcome this problem, a narrowband measurement setup utilizing a synchronized clock and a network analyzer was developed. The measurement setup is shown in Figure 12. The microcontroller’s clock originates from a high-precision clock generator. The network analyzer is set to the tuned-receiver mode, in which the internal reference clock is replaced by the external synchronized signal generator. The signal generator and the center frequency of the network analyzer are set to the same harmonic frequency, 96 MHz. S11 was measured for both magnitude and phase. In this case, phase is given relative to the microcontroller clock. The magnitude and phase of the magnetic ﬁelds over the 100 pins is shown in Figure 13. The result shows that the current on the Vdd and Vss pins are 180 degrees out of phase as expected, with the highest current on Vdd pins 12, 41, 67 and 92. The return current is on Vss pins 9, 13, 21, 42, 51, 66, 84 and 93. The currents on adjacent Vdd pins and the Vss pins do have different amplitudes, possibly causing an unbalanced current across the package. Such unbalanced currents have been associated with higher TEM cell emissions.2 10 MHz synchronization Clock generator Signal generator 192 MHz, 10 dBm -20 dBm attenuator Reference channel in Network analyzer Oscillator in 6 MHz, 7 dBm Automotive microcontroller PLLx8, Main clock frequency = 480 MHz Near-field scan loop probe Network analyzer port 1 tunedreceiver mode D C LNA A–B 180° hybrid junction Figure 12. Setup for measuring magnitude and phase of package-pin currents Pin 1−100 0 −10 Normalized power (dBm) −20 −30 −40 −50 −60 10 20 30 40 50 Pin number 60 70 80 90 100 Figure 13. Magnitude and phase distribution of magnetic ﬁelds over package pins, measured at the second harmonic of the clock 150 Relative phase (degree) 100 50 0 −50 −100 −150 10 20 30 40 50 Pin number 60 70 80 90 100 48 Agilent Measurement Journal

Table of Contents Feed for the Digital Edition of Agilent Measurement Journal - Issue 3 - 2007

Applying Ingenuity to the Measurement of Emerging Technologies Contents Emerging Innovations Department Delivering Bigger Benefits by Optimizing Customer Workflows Measuring Material Properties at the Nanoscale Utilizing In Situ Atomic Force Microscopy in Life Science, Pharmaceutical and other Bio-Related Applications WiMAX™: Plotting a New Path to Global Mobility Addressing the Triple Complexity of Triple-Play Networks What Next for Mobile Telephony? Exploring the Inner Workings of Tire-Pressure Monitoring Systems Developing, Assessing and Applying a High-Resolution Thin-Film Magnetic Probe Making Accurate Settling-Time Measurements Using a Vector Network Analyzer Applying Metabolomics Methods to the Study of Bacterial Leaf Blight in Rice Plants Measuring Stream Dynamics with Fiber Optics survey

Agilent Measurement Journal - Issue 3 - 2007

For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.