Anatomy of a PCIe Link

Figure 1: A PCIe link between root complex and end point.
Each device has its own transmitter and receiver.

Peripheral Component Interconnect Express (PCIe®) is a high performance, general-purpose input/output (I/O) interconnect designed for a wide variety of computing and communication platforms. Recent iterations of the standard take advantage of high-speed serial technology, point-to-point interconnects, switch-based technology, and packetized protocol. They rely heavily on link negotiation and link training, so much so that being able to capture and view dynamic link behaviors is essential to debugging PCIe devices. Nevertheless, it remains a pain point for PCIe engineers. Why is it so difficult? To start, let’s break down the PCIe architecture to understand what is going on.

How to Test Noisy Power Supply Outputs

Figure 1: 3.3 V output of a DC-DC converter.
The waveform shows the nominal DC level,
ripple and high frequency noise bursts.

Did you ever acquire the output of a power supply with your oscilloscope and find an unexpectedly high level of noise? Did you try adding filter capacitors only to find the noise level was not changed? 

In this post, we'll discuss how the choice of probe affects the noise present in power measurements, as well as how oscilloscope settings such as termination impedance, bandwidth and coupling can be adjusted to lessen noise and improve measurement results.

Figure 1 shows a typical DC-DC converter output measurement. The mean value of the waveform is 3.294 V.  Ripple appears at the switching frequency of 1.2 MHz, and noise in the form of high frequency bursts and baseline thickening is visible throughout.

Waveforms like this can be acquired with a 10:1 high impedance probe, a 1:1 coaxial cable connection, or a 1.2:1 rail probe using either DC or AC coupling, as available.  Figure 2 summarizes how each oscilloscope/probe configuration affects the measurement.

MAUI Studio Pro: Generating Waveforms

Figure 1: MAUI Studio Pro lets you generate
multiple waveform types from equation.

MAUI® Studio includes a simple waveform generator that enables you to create any of six standard waveforms or a DC current simply by enter a few waveform properties, such as frequency and amplitude. The waveforms are continuously generated and act like a live, repetitive waveform acquisition for simulation exercises. 

MAUI Studio Pro adds to that a true, arbitrary function generator. Numerous different waveform types can be generated from equation, and custom jitter/noise characteristics can be added to any generated waveform. 

MAUI Studio Pro: Analyzing Anyone's Waveform Data

Figure 1: A waveform file (.bin) saved on a Keysight 
oscilloscope undergoes multiple math and measure
 operations in MAUI Studio.

 Another key feature of MAUI® Studio and MAUI Studio Pro is the ability to recall waveform files saved on other vendors' oscilloscopes, as well as on Teledyne LeCroy oscilloscopes. The software supports files saved on Tektronix (.wfm), Keysight (.bin), Rohde & Schwarz (.bin) and Yokogawa (.wvf) instruments. It even lets you filter for these types when browsing for files. And with some simple editing, "time and data with header" format  Excel (.csv) files can also be recalled into MAUI Studio, extending its analysis capabilities to waveforms acquired from nearly any type of instrument or sensor.