What are some common causes of noise and distortion in oscilloscope signals?

Oscilloscopes are powerful tools for measuring and analyzing electrical signals, but they can also be affected by noise and distortion that degrade the quality and accuracy of the displayed waveforms. Noise and distortion can come from various sources, such as the oscilloscope itself, the probe, the signal source, the environment, or the user. In this article, you will learn about some common causes of noise and distortion in oscilloscope signals and how to identify and minimize them.

1 Oscilloscope noise

Oscilloscope noise is the random or unwanted variation in the voltage or current of the signal that is inherent to the oscilloscope. It can be caused by factors such as the bandwidth, the sampling rate, the resolution, the input impedance, the trigger system, or the analog-to-digital converter (ADC) of the oscilloscope. Oscilloscope noise can be reduced by using appropriate settings, such as lowering the bandwidth, increasing the sampling rate, using averaging or filtering functions, adjusting the trigger level and slope, or using a higher-resolution oscilloscope.

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James Beams

Senior Hardware Development Engineer at Apple
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The most common source of unwanted noise is poor (or disconnected) probe grounding. Connect the probe ground as close to the signal as possible, use the shorted ground lead as possible (avoid a large ground loop), and make sure it is a ground that is referenced to the signal you are probing.

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Gursimran Singh

Analog Engineer @ Texas Instruments | Mixed-Signal Integrated Circuits | Hardware software co-design | Brain Computer Interfaces
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A good starting point is ensure that you have a good ground. The second suspect is the probe being used, most oscilloscope have the ability to generate a known signal such as a square or a sine wave that you can use to check your probe. If there seems to be noise on the ground, you can try using a differential probe if the scope supports it.

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Mina Ejmalian

PCB layout Design Engineer| Leiterplattenentwicklerin | Schaltungsdesign | Entwicklerin für PCB-Design
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Common causes of noise and distortion in oscilloscope signals include power supply ripple, ground bounce, mechanical vibration, movement in the probe tip, and input amplifier noise. These factors can obscure the true signal, leading to inaccurate measurements and analysis

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2 Probe noise

Probe noise is the noise that is introduced by the probe that connects the signal source to the oscilloscope. It can be caused by factors such as the probe type, the probe tip, the probe ground, the probe compensation, or the probe cable. Probe noise can be reduced by using a suitable probe for the signal frequency and amplitude, using a sharp and clean probe tip, using a short and low-inductance probe ground, adjusting the probe compensation to match the oscilloscope input, or using a shielded or coaxial probe cable.

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Waseem Alkhayer

Electronics | Technology | IoT | Startups
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Make sure to use a Low inductance ground clip "spring" with your probe while doing in your measurements. Avoid using the long lead ground wire as this might screw up your measurement. This is a key for successful probing especially when dealing with high speed signals. The key point is to minimize inductance, since a standard 6" ground probe has an inductance of 150nH or so. Couple that with the "high" impedance *10 probe's 15pF tip capacitance, and you have an resonance at ~100MHz. You minimize inductance by keeping the length short.

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Michael Menshikov

Electronics Engineer, FPGA Design Engineer, Embedded Software Engineer🛸Let's connect!👽
(edited)
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The main problem in measuring is not noise. We want to see real hindrances and noise on the board. The main problem when measuring is signal distortion and additional noise. The signal's shape and noise level often depends on where we take the ground signal for the oscilloscope probe. Therefore, in order for the signal to have minimal distortion, it is necessary to take the ground signal as close as possible to the signal being measured, and to have the ground wire of the oscilloscope probe as short as possible. It is often convenient to solder short thin wires and connect an oscilloscope to them. For important signals on the board, it is useful to have special probe points for an oscilloscope probe or even for a coaxial cable.

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3 Signal source noise

Signal source noise is the noise that originates from the signal source itself or from the circuit that generates or modifies the signal. It can be caused by factors such as the power supply, the signal generator, the amplifier, the resistor, the capacitor, or the transistor. Signal source noise can be reduced by using a clean and stable power supply, using a low-noise signal generator, using a high-quality amplifier, using low-noise or precision components, or using proper shielding and grounding techniques.

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4 Environmental noise

Environmental noise is the noise that is picked up by the signal source, the probe, or the oscilloscope from the surrounding electromagnetic fields or interferences. It can be caused by factors such as the power lines, the lighting, the radio waves, the cell phones, the computers, or the other electronic devices. Environmental noise can be reduced by avoiding or minimizing the exposure to these sources of noise, using a metal enclosure or a Faraday cage for the signal source or the oscilloscope, using twisted-pair or coaxial cables for the signal and probe connections, or using ferrite beads or chokes to suppress the noise currents.

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Gursimran Singh

Analog Engineer @ Texas Instruments | Mixed-Signal Integrated Circuits | Hardware software co-design | Brain Computer Interfaces
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Many approaches can be taken to minimise environment noise in your system. Alternating ground traces with signal traces is one way to avoid cross-talk between signals and the noise associated with it.

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5 User noise

User noise is the noise that is caused by the user's actions or mistakes when using the oscilloscope. It can be caused by factors such as the probe placement, the probe loading, the ground loop, the aliasing, or the improper settings. User noise can be reduced by following some best practices, such as placing the probe as close as possible to the signal source, using a high-impedance probe to avoid loading the signal source, avoiding connecting multiple grounds to the same point, using a high enough sampling rate to avoid aliasing, or using the correct settings for the signal type and frequency.

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6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?

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What are some common causes of noise and distortion in oscilloscope signals?

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1 Oscilloscope noise

2 Probe noise

3 Signal source noise

4 Environmental noise

5 User noise

6 Here’s what else to consider

Electronic Circuit Design

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