D9010POWA Power Integrity Analysis with N7020A and N7024A Power Rail Probes

D9010POWA

Power Integrity Analysis with N7020A and N7024A Power Rail Probes

Introduction

The Keysight Power Integrity Analysis application works optimally with the N7020A and N7024A Power Rail probes. The analysis application lets users define a DC supply as either a victim of or an aggressor to, other periodic transitioning signals and quantifies the amount of adverse interaction involved. In this way, users can see what their DC supply and/or digital signals would look like if they were immune to the negative effects of each other. With this insight, users can make informed decisions about what, if any, the next steps they would take to clean up their DC supplies.

The Need for a Specialized Power Integrity Probe

Would you like to minimize oscilloscope and probe noise when measuring DC power rails? Do you need more offset than is available in your oscilloscope so you can zoom-in to view and analyze small signals on top of DC power supplies? Would you like to have input impedance greater than 50 Ω at DC so your oscilloscope doesn’t load your DC power rails? Do you need more bandwidth so you can track down transients on your DC power supplies that can adversely affect your clock and data? If so, the Keysight Technologies, Inc. N7020A and N7024A power rail the right tool for the job.

Developed specifically to help engineers with precise DC power rail testing, the N7020A and N7024A power rail probes were designed to minimize noise and maximize the offset range of the measurement system while providing high bandwidth and low target loading.

The Challenge

The increased functionality, higher density, and higher frequency operation of many modern electronic products has driven the need for lower supply voltages. It is common in many designs today to have 3.3, 1.8, 1.5 and even 1.1 V DC supplies — each of them having tighter tolerances than in previous product generations.

Engineers need to zoom-in on power rails to look for transients, measure ripple, and analyze coupling. An oscilloscope often does not have enough offset to be able to shift the DC power rail to the center of the screen for the required measurements. Even if the oscilloscope being used has enough offset to center the supply on the screen, the oscilloscope will load the supply with 50 ohms to ground and sink 30mA per volt of the supply. This can change the behavior of the supply resulting in inaccurate characterization. Placing a DC blocking capacitor in the signal path eliminates the offset problem but also eliminates relevant DC information such as DC supply compression or low-frequency drift.

A low noise measurement solution is of paramount importance so it doesn’t confuse the noise of the probe and oscilloscope with the noise and ripple of the DC supply being measured. Using probes (active or passive) that are higher than 1:1 attenuation can help with the offset difficulty but will also decrease the signal-to-noise ratio and negatively affect measurement accuracy. Using the oscilloscope’s 50 Ω input with a passive coaxial cable offers a 1:1 attenuation ratio probing method but results in higher-than-desired DC loading of the supply being measured and has the offset limitations mentioned earlier.

Ripple, noise, and transients riding on DC supplies are a major source of clock and date jitter in digital systems. Dynamic loading of the DC supply by the processor, memory, or similar items occurs at the clock frequency and can create high-speed transients and noise on the DC supply that can easily have content above 1 GHz. Consider the case of a high-speed digital design such as USB3.1 with 10Gbps data rates creating switching transients at 5GHz. Designers need high-bandwidth tools to evaluate and understand high-speed noise and transients on their DC power rails.