As the frequency of the test signal is increased, the amplitude of the seen signal lowers by -3 dB or 70.7 percent of its real value, which is known as oscilloscope bandwidth. The fundamental ability of an oscilloscope to measure a signal is determined by its bandwidth.
The oscilloscope’s capacity to accurately show the signal reduces as the signal frequency increases. The frequency range that the oscilloscope can accurately measure is shown by this specification.
What Is Oscilloscope Bandwidth
If the input signal is a sine wave, the oscilloscope’s bandwidth must be equal to or larger than the input signal’s fundamental frequency. A bandwidth of 5 or more times the fundamental frequency is a sufficient starting point for non-sinusoidal waveforms such as square waves, pulses, digital communications, etc.
However, it may be too low for accurate rise time measurements. It’s possible that a bandwidth of 10 times the fundamental frequency or 1st order harmonic would be more suitable.
What Is Measurement Bandwidth
The amount of data that may be transported from one point to another inside a network in a given amount of time is referred to as bandwidth. It is a connection’s transmission capacity and is an important aspect in evaluating a network’s or internet connection’s quality and speed. Typically, bandwidth is measured in bits per second and expressed as a bitrate (bps).
High-frequency microwave power sensors can be utilized for wide-bandwidth measurements, while the IF frequency is determined by the OSA in the measurement setup, which is the differential between the optical frequencies of the two CW light sources.
Comparing With the Flow of Water
There are various methods for determining bandwidth. Some metrics are used to calculate current data flow, while others are used to determine maximum flow, typical flow, or good flow. Bandwidth is comparable to the flow of water via a conduit. The pace at which water (data) flows through the pipe (connection) under varied conditions is referred to as bandwidth.
We could measure liters per minute instead of bits per second. The maximum bandwidth is represented by the quantity of water that could conceivably flow through the pipe, whereas the current bandwidth is represented by the amount of water that is now flowing through the pipe.
What Is Oscilloscope System Bandwidth and How Do I Find the Bandwidth of the Scope Probe
System bandwidth refers to the bandwidth that is the result of using both oscilloscope and probe together. The bandwidth of an oscilloscope and a probe is the frequency at which the amplitude of the input signal attenuates by 3 dB.
As a result, if your scope’s datasheet indicates a bandwidth of 100 MHz, you can count on measuring at least 70% of your signal amplitude at that frequency. The same may be stated about your probe. The problematic aspect is that when you use them together or the system bandwidth, may not be 100 MHz.
While we acquire the scope’s bandwidth from the vendor, we reduce the system bandwidth as soon as we add a cable, probe, or amplifier to the scope. The new system bandwidth is just as vital to understanding as the scope’s bandwidth, but it’s difficult to evaluate outside of a calibration facility.
Quick Method
Using a wide-band noise source, we present a straightforward approach for evaluating the transfer function and system bandwidth of any probing system.
Measuring Transfer Functions
A measuring system’s transfer function can be measured in a variety of ways. A sine wave source with a flat frequency response could be used. We might measure the amplitude of the sine wave at various frequency stages by sweeping its frequency from 1 MHz to 10 GHz.
Quick, Simple Way to Measure the System Bandwidth of a Scope-Probe System | 2019-01-18 | Signal Integrity Journal
This necessitates a sine wave source with an extremely flat frequency response and a large bandwidth. Also, we may utilize an extremely quick step signal as an input. The spectrum of a 10 MHz clock, for example, would be a comb pattern with peaks at odd multiples of 10 MHz.
However, because the amplitude of each harmonic decreases as 1/f, the signal-to-noise ratio (SNR) decreases at higher frequencies, where the transfer function roll-off is more important.
Using a Noisecom NC1100 Wide-Band Noise Source
A Noisecom NC1100 wide-band noise source with frequency components ranging from 1 MHz to > 10 GHz is used in the method presented here. We use the maximum bandwidth connection possible to measure this signal at the input to the Teledyne LeCroy WavePro HD 804, calculate its FFT, etc.
It helps to acquire the spectrum, and use this as the stimulus. The cables and probes are then inserted, and the changing response is measured. The ratio between the distorted spectrum and the reference spectrum is a measure of the transfer function of simply the cable-probe system on a log amplitude scale.
This method not only provides information about the probes and interconnects but also provides information on how the scope reacts to the measurement system, which cannot be measured.
The bandwidth of the 10X Probe
The 10x probe is a complicated probing system in and of itself. A low-pass filter with a roll-off frequency of around 10 kHz, a parallel high-pass filter with a pole frequency of around 10 kHz, and a unique, very lossy coax cable that absorbs and attenuates any high-frequency reflections in the cable are all built into it.
To use the 10x cable, the scope must have a 1 Meg coupling. Due to the scope amplifier, the measuring system bandwidth is automatically reduced to around 1.2 GHz. The tip of the probe is changed with a coax adaptor to view the probe’s absolute greatest bandwidth. This isn’t your standard 10x probe, which has a significant loop inductance at the tip.
Conclusion
Bandwidth is an important specification of an oscilloscope on which the final output depends vastly. While the scope bandwidth is an important figure of merit for describing the scope’s highest frequency component, modifying the scope’s input coupling and adding cables and probes would reduce the measurement bandwidth.
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