You need to test, we're here to help.

You need to test, we're here to help.

25 July 2022

Signal and Power Integrity Tutorial: How PDN Design Affects Board-level Noise

Figure 1. Oscilloscope traces resulting from 
measuring a 3.3. V power rail with a 10x probe
versus a coaxial connection, with an
adjacent 10x probe acting as an RF antenna.
By Prof. Eric Bogatin,
Teledyne LeCroy Fellow

Excerpted by permission from the Signal Integrity Journal article, Measuring Only Board-level Power Rail Noise May Be Misleading

In our blog, we’ve presented a lot about the impact of the interconnect on oscilloscope measurements, and how where you probe can be as important as how you probe. This article is an excellent demonstration of those very principles.

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Power rail measurements are important because they can identify potential sources of noise before they become a problem. However, measuring only the power rail noise at the board-level may be a misleading indication of the noise the die actually sees. 

Best Practices for Power Integrity Measurements

Measuring a power rail on a board seems like a simple task. Like all measurements, it is easy to get a waveform on the oscilloscope’s screen, but it is difficult to have confidence you have eliminated the measurement artifacts and have a realistic measure of the actual signal present.

05 July 2022

A Tale of Two Calibrations: Vector Network Analyzer vs. WavePulser 40iX

Figure 1: This sequence diagram of the
classic SOLT 2-path calibration shows
the order of connections required. 
It was the best of S-parameter measurements, it was the worst of S-parameter measurements…and the difference was in the calibration.  Calibrating a vector network analyzer (VNA) before making any measurements is required in order to reduce errors from imperfect channel matching, less than optimal directivity in the directional couplers and cable response issues. While VNAs are precisely calibrated at the factory, that calibration only extends to the front panel measurement ports. There will inevitably be drift on the internal paths over time. Also, any cables, adaptors or fixtures connected to the measurement ports must be characterized and de-embedded in order to make exact measurements of the device under test (DUT).  

There are many possible calibration methods depending on the number of ports and paths being measured.  For simplicity, let’s consider the common 2-port, 2-path calibration.  This calibration method will yield a full set of S-parameters for the two ports: S11, S12, S21 and S22.  It requires the use of a short, open, load and through (SOLT) calibration reference standard, along with the cables used in the test setup, as shown in Figure 1.