Oscilloscope Basics: When to Use Track to Graph Oscilloscope Measurements

Figure 1: Pulse Width Modulated waveform (yellow)
and Track math operator (blue),
where the X-axis scaling is identical for both.

Modern oscilloscopes contain many tools that can be used for analyzing data, including Track and Trend math functions. Both Tracks and Trends graphically display measurement results and locate anomalies. The main similarity between Tracks and Trends is that the Y-axis of both operators is the measurement parameter itself (for example, Pulse Width, Duty Cycle, Rise Time, Slew Rate, etc.). The main difference between the two math operators is their X-axis, in which the Track uses the identical X-axis and synchronous horizontal scaling as the input waveform, whereas the Trend uses units of chronology. A Track, in essence, is a waveform of the measurement values. A Trend is a data logger showing the history of change in measured parameter values, but points are not necessarily synchronous with the measured waveform.

Use Tracks for Anomaly Detection

The Track provides valuable debugging information by directly pointing to an area of interest. 

Notice the negative-going spike in the Track waveform in Figure 1. Figure 1 occurs at the point in time where the input waveform reaches its most narrow pulse width, and the Track instantly finds it, indicating when one measurement deviates from the others in the graph. The Track identifies the exact location in time where the narrowest or widest pulse width has occurred, and fully describes the measurement changes occurring throughout the entire waveform. Since oscilloscopes can acquire thousands or even millions of waveform edges within a single acquisition, the Track allows an engineer to quickly "find the needle in a haystack".

PCI Express 4.0 Error Detection Using a BERT and Oscilloscope

Figure 1: BERT and Oscilloscope connection
for PCI Express 4.0 error detection.

The PCI Express® 4.0 standard specification requires an oscilloscope with at least 25 GHz analog bandwidth and a BERT which can test bit rates of at least 16 Gbps. The BERT provides a known input pattern to the PCIe® device under test (DUT), and the DUT is instructed to regenerate the identical bit pattern while placed in loopback mode. Since a BERT can output a signal when a bit error is detected, this signal can be input to the oscilloscope to trigger a synchronized capture when an error occurs. By combining the capabilities of these two instruments, a powerful combination of real-time error detection and characterization can emerge.

Connecting the Instruments

In Figure 1, a known pattern is connected from the BERT PPG D1 output to the PCIe DUT input via a 2.92 mm K-type cable. The DUT attempts to regenerate the same data pattern, while the DUT output is routed to both the BERT error detector input and the oscilloscope channel 1 via 2.92 mm K-type tables and a power splitter. An error-free reference signal is connected between the BERT D2 output to the oscilloscope channel 2, along with the error trigger signal from the error detector output to the oscilloscope channel 3. An oscilloscope Edge trigger is set on the rising edge of the error detector output signal on C3.

WavePulser 40iX vs. Time Domain Reflectomer (TDR) or Vector Network Analyzer (VNA)

Figure 1: S-parameters and TDR responses are two means to
the same end, characterizing interconnects.

Oscilloscopes are used to measure signals, usually as voltages vs. time, and signals come from active devices. But interconnects are passive structures that don’t produce their own signals. To characterize interconnects, you need a stimulus-response system.

There are two, principal types of stimulus-response systems used to characterize interconnects: Vector Network Analyzers (VNAs) used to measure S-parameters in the frequency domain, and Time Domain Reflectometers used to measure impulse responses in the time domain. Each uses a different type of incident signal and a different formalism, but as long as the interconnect is linear, passive and time invariant, both S-parameters and impulse responses yield the same information content in different formats and can be translated from one into another.

So, which do you need? We’ll look briefly at what each does and what are the criteria that might require you to have one versus the other.

Configuring Dynamic Oscilloscope Measurements Using Advanced Customization

Figure 1. The Advanced Customization option
lets you seamlessly and continuously update the
input of one parameter with the output of another.

With the installation of the Advanced Customization (XDEV) option on Teledyne LeCroy MAUI® oscilloscopes, you can create a measurement parameter whose input value is dynamically updated with each new trigger by the output value of another measurement parameter. All that is required is three simple lines of VBScript. 

To demonstrate, we’ll use the example of taking the x@max value measured on each acquisition and using it to dynamically populate the X position used by the measurement parameter lvl@x. However, these principles could be applied to any two parameters that share a logical/mathematical relationship, or to a parameter and a math function (for example, to use the output of a parameter as the multiplier for a Rescale function).