A Walk-Through of Ground-Bounce Measurements

Figure 1: The trigger pulse from the
MCU is one clock cycle in width

In earlier posts in this series, we've explained what ground bounce is and how it happens. We have also taken a deeper dive into the use of I/O drivers to implement sense lines that let us better quantify and analyze what kind of ground-bounce hit our system is taking. Now, let's look at a detailed example of how to measure and diagnose ground bounce.

Investigating IoT Wireless Signals (Part II)

Figure 1: This screen capture depicts frequency demodulation
and subsequent Manchester decoding of the bit stream

Internet of Things (IoT) devices must communicate with their peers--other IoT devices--as well as with the host system that governs their activities. In our previous post, we examined how to perform amplitude and frequency demodulation of RF bursts, such as Bluetooth Low Energy (BLE) advertising bursts. We'll continue with other methods of analyzing RF signals.

Investigating IoT Wireless Signals

Figure 1: Many IoT devices accept
wireless antennas using U.FL
connectors

Many IoT devices use wireless methods to communicate with other devices or with host systems. Just as with DC power-rail signals, probing of RF signals should be done with as little noise and as non-invasively as possible and with the best possible signal fidelity. Effective probing opens the door to Wi-Fi and Bluetooth signal analysis with RF demodulation, vector signal analysis, and spectrum analysis.

Anatomy of an IoT Device

Figure 1: IoTs include SOCs, DDR,
DPM ICs, wireless, and MCUs

There's already more Internet of Things (IoT) devices deployed than there are humans on Earth. That gap will increase radically in coming years, and the explosion in IoT devices means a commensurate explosion in the need for debugging tools. So what's in an IoT device to debug, anyway?

Making On-Die Power-Rail Measurements (Part III)

Figure 1: This screen capture shows
the idle-state conditions

Having reviewed the test setup for on-die power-rail testing and our expectations of what the tests should show us, let's walk through the measurements and look over the results. We'll also note whether our results align with our expectations or are outside of those expectations.

Making On-Die Power-Rail Measurements (Part II)

Figure 1: When switching from low to
high, PDN noise flows from the Vdd
rail through to the Vss rail

Now that we're ready to begin some on-die power-rail measurements, it's a good idea to step back for a moment and anticipate what these measurements should show us. What actually happens on the die when CMOS gates are switching on and off? What should we expect to see on the on-die power rails? And what happens at the clock edges?

Making On-Die Power-Rail Measurements (Part I)

Figure 1: Our test setup for the
on-die measurement examples

Our exploration of on-die power-rail measurements has brought us to the point of demonstrating some examples of these measurements. As noted in the prior post, we will use an Atmel 328 microcontroller demo board, prepared with firmware to control it explicitly for our purposes, and with coaxial cable in place on the bottom of the board to serve as transmission lines for our signals of interest.

Measuring Shared On-Die Power Rails

Figure 1: This schematic represents the signal paths
in typical, general-purpose I/Os

If you're taking power-rail measurements on a semiconductor die that is appropriately instrumented with sense lines and a direct connection to the die's core PDN, you're in pretty good shape. But what if that's not the case? If the die's I/O power rails are shared by the core power rails, here's a way to get your core power-rail measurements anyway.

Power-Rail Noise: Small Signal, Big DC Offset

Figure 1: Your
scope's vertical
adjust has its
limits

We've been working through the various challenges in making power-rail noise measurements. One of those challenges is RF pickup that can often swamp the noise signal, and the way around that is to ensure a coaxial connection from the oscilloscope's input down to the power rail itself. We want a high signal-to-noise ratio (SNR), so we're better off with a 1X probe than with a 10X attenuating probe. We want high bandwidth, so we want a 50-Ω termination at the oscilloscope input.