X-Y Mode
Precision Phase Measurement with a Touch of Engineering Romance
Keywords: Lissajous Figures, Phase Accuracy, Deskew, V-I Curve, B-H Curve, Oscilloscope Art
An oscilloscope is an instrument used to display the relationship between time and amplitude. Its primary functions include time measurement, amplitude measurement, and waveform observation. Beyond visualizing how signals vary over time, the X-Y mode replaces the time axis with the amplitude of another input channel—a capability that has existed since the era of analog oscilloscopes. With the advent of digital oscilloscopes, signal analysis expanded further through the use of Fast Fourier Transform (FFT) to reveal the relationship between frequency and amplitude. More recently, time-frequency analysis, commonly presented as a spectrogram (also known as a spectral waterfall display), has enabled visualization of how frequency content evolves over time. As a result, modern digital oscilloscopes have become versatile measurement platforms spanning three domains: the time domain (Y-T), the frequency domain (FFT), and the time-frequency domain (Spectrogram). This article focuses on the long-established X-Y mode, exploring its practical applications and demonstrating how this classic measurement technique can also be leveraged to create highly creative and visually compelling displays.
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What Is X-Y Mode?
In a conventional oscilloscope, the horizontal axis (X-axis) represents time. In X-Y mode, however, the time axis is replaced by the amplitude of another input channel. Using a dual-channel oscilloscope as an example, Channel 1 is assigned to the X-axis, while Channel 2 is assigned to the Y-axis.
Under this configuration, each point displayed on the screen is defined by the coordinate (VCH1, VCH2).
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Application 1: Lissajous Figures
When two sinusoidal signals are applied to the X and Y channels respectively, the oscilloscope displays a distinctive geometric pattern known as a Lissajous figure. This provides one of the most intuitive methods for determining the frequency ratio and phase difference between two signals.
Interpreting Frequency and Phase
• Frequency Ratio: The frequency ratio can be determined by counting the number of intersections (or tangency points) of the pattern with the horizontal and vertical boundaries of the display.
• Phase Difference: When the two signals have the same frequency, the shape of the Lissajous figure varies with the phase difference:
o Phase 0o : A straight line with a positive slope (see Figure 3).
o Phase 90o : A perfect circle, provided that the gains of the X and Y axes are equal (see Figure 4).
o Phase 180o : A straight line with a negative slope (see Figure 5).
(Reference Figures 1-5 for multi-frequency and phase-variable acquisition results using the MPO-2204P internal AFG).
Figure 1: Time-domain waveforms and X-Y mode display showing a frequency-doubling relationship, where Signal Generator 1 outputs a 100 kHz sine wave and Signal Generator 2 outputs a 200 kHz sine wave using the built-in generators of the MPO-2204P.
Figure 2: Time-domain waveforms and X-Y mode display illustrating a 4:1 frequency relationship, where Signal Generator 1 outputs a 100 kHz sine wave and Signal Generator 2 outputs a 400 kHz sine wave using the built-in generators of the MPO-2204P.
Figure 3: Time-domain waveforms and X-Y mode display showing two 100 kHz sine waves with a 0° phase difference, generated by the built-in signal generators of the MPO-2204P.
Figure 4: Time-domain waveforms and X-Y mode display showing two 100 kHz sine waves with a 90° phase difference, generated by the built-in signal generators of the MPO-2204P.
Figure 5: Time-domain waveforms and X-Y mode display showing two 100 kHz sine waves with a 180° phase difference, generated by the built-in signal generators of the MPO-2204P.
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Application 2: Phase Accuracy
In Y-T mode, when a small time difference exists between the signals on Channel 1 and Channel 2, the difference is often difficult to detect visually. X-Y mode, however, provides higher phase resolution. Even when the input signals are identical, if the PCB trace lengths between the two oscilloscope channels differ, the display will show a thin ellipse instead of a straight line (see Figure 6).
X-Y Mode Specification Examples:
• Example 1: GOS-6112 100 MHz analog oscilloscope: Phase error < 3° from DC to 50 kHz; X-axis bandwidth DC to 500 kHz (-3 dB)
• Example 2: GDS-3104A 1 GHz digital oscilloscope: ±3° at 100 kHz
Figure 6: Time-domain and X-Y mode display results when the MPO-2204P built-in signal generator 1 outputs a 100 kHz sine wave, and generator 2 outputs a 100 kHz sine wave with a 2° phase difference.
When performing precise power calculations (such as P = V*I), even a very small phase error can lead to significant power measurement inaccuracies. This is why the subsequent time-delay calibration (“Deskew”) for the voltage and current probes is critically important.
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Application 3: Deskew (Time-Delay Calibration) for Voltage and Current Probes
In power testing, CH1 is often connected to a voltage probe and CH2 to a current probe. Using the oscilloscope’s calculation functions, one can obtain power waveforms or use X-Y mode to plot the SOA (Safe Operating Area) of power devices. However, the current probe contains a transformer and amplification circuitry, or may have a different cable length compared to the voltage probe, resulting in conduction delays. If this time difference is not calibrated, measurement errors will occur. For compound semiconductors such as silicon carbide (SiC) and gallium nitride (GaN), which switch faster than conventional MOSFETs and can effectively reduce switching loss, uncorrected probe delay differences can lead to significant errors in switching loss measurements.
Deskew Procedure:
1. Use a dedicated fixture: Use a Deskew Fixture (see Figure 7), which simultaneously outputs high-frequency voltage and current signals with steep rising edges.
2. Observe X-Y overlay: Connect the two channels and switch to X-Y mode.
3. Adjust the delay: Adjust the Deskew parameter in the oscilloscope menu until the original ellipse shrinks into the narrowest straight line.
This step compensates for typical transmission delay differences of 10 ns to 50 ns.
Figure 7: GKT-100 Deskew Fixture
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Application 4: Semiconductor V-I Curve or Magnetic Component B-H Curve
By measuring with voltage and current probes, X-Y mode can be used to observe the V-I curve of a semiconductor. Using calculations to convert the voltage and current waveforms into magnetic flux density (B) and magnetic field strength (H), the B-H curve of a magnetic component can be obtained.
Formulas for converting voltage and current into magnetic flux density (B) and magnetic field strength (H) can be found at the following link:
>>> How to use a digital oscilloscope to produce the dynamic B-H Curve of magnetic components?
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Application 5: Creative Application – Drawing with an Oscilloscope (Oscilloscope Art)
X-Y mode is not only a measurement tool but can also serve as a canvas for digital art. The principle is to convert image coordinates into time-varying voltage sequences. These voltage sequences are then generated as waveforms by an arbitrary waveform generator. When the waveforms are fed into the oscilloscope and set to X-Y mode, the image appears on the screen. The example below shows a “matching hearts” drawing. X-Y mode, therefore, is not only a powerful tool for phase measurement but also a way to express the unique creativity and romantic side of engineers.
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Figure 8: MPO-2204P built-in signal generator used to generate two sets of arbitrary waveforms, producing X-Y mode display results of “Matching Hearts” and the text “I LOVE YOU.”
At the time of writing, it was on the eve of Valentine’s Day 2026. Finally, let AI write a warm Valentine’s Day greeting for electronic engineers.
May your life voltage always remain at High Level, and may all worries be perfectly filtered out by a low-pass filter, leaving only the purest joy and heart-throbbing moments.
May our relationship be like a superconductor with zero resistance, and may our communication always be noise-free. On this special day, may your PCB routing lead straight to happiness, your energy conversion efficiency remain at 100%, your power fully charged, and your love uninterrupted.
Happy Valentine’s Day! Tonight, may your system run stably without any need to debug, and may you simply enjoy this exclusive frequency synchronization.
Contact Us:
Diana
Digital Service Specialist
E-mail: diana@goodwill.com.tw