Oscilloscope Bandwidth Vs Sample Rate | Understanding the Relationship Between Bandwidth and Sample Rate
Bandwidth and sample rate are the two most important features of an oscilloscope. Bandwidth is the frequency range that an oscilloscope can accurately measure. And sample rate is the number of data readings that an oscilloscope takes per second.
Bandwidth is the most important feature of an oscilloscope. Without enough bandwidth, an oscilloscope will show a distorted version of a signal. And, the sample rate is the second most important feature of an oscilloscope. The accuracy of an oscilloscope is directly proportional to the sample rate.
The Major Distinction Between Oscilloscope Bandwidth and Sample Rate
Bandwidth and sample rate are two important features of an oscilloscope. The performance and accuracy of an oscilloscope are directly proportional to its bandwidth and sample rate. To understand this topic better we must learn about bandwidth and sample rate in detail.
Bandwidth
Bandwidth is the frequency range that an oscilloscope can accurately measure. It is measured in hertz. An oscilloscope is like a low pass filter that allows frequency from 0Hz up to a certain value to pass. Like a filter, the cutoff point of an oscilloscope is the 3dB down point of the filter.
If an oscilloscope’s bandwidth is less than the input signals frequency then the signal will be attenuated and we won’t see much of the signal. Even it is not recommended to use a 100MHz oscilloscope to measure a 100MHz signal. We will see some distortion in the signal.
On the other hand, if the oscilloscope has too much bandwidth than the input signal, we will see high-frequency noises and the measurement won’t be clean. So, oscilloscope bandwidth should be adequately more than the signal frequency to reduce noise and eliminate distortions.
Sample Rate
The sample rate is the number of readings an oscilloscope can make per second. A sample is just a piece of data of a signal, the more samples we have, we can recreate the signal more accurately. The rate of sampling must be fast enough to get an accurate signal recreation.
According to Physicist Harry Nyquist, the sampling rate of an oscilloscope must be greater than at least twice the frequency of the highest frequency component of the signal for proper reconstruction of the signal without errors.
FSampling > 2FSignal
Bandwidth Vs Sample Rate
Bandwidth is the most important characteristic of an oscilloscope. Because it defines the operating range of an oscilloscope. The second most important feature is the sampling rate. Because without enough waveform data the frequency of the signal, exact rise and fall times, and the height and shape of the signal cannot be properly displayed.
How Much Oscilloscope Bandwidth Is Needed
The bandwidth requirement of an oscilloscope depends on the intended application of the oscilloscope. For general purposes a 70-100MHz oscilloscope is adequate. Here the rule of thumb is, that the bandwidth must be greater than the frequency it will be used to measure.
What Is a Good Sampling Rate for an Oscilloscope
A sample rate of 1-2Gs/s (giga-samples per second) is good enough for general-purpose applications. For accurate reconstruction of the input signal, modern oscilloscopes have at least 5 times more sample rate than the bandwidth of the oscilloscope. But the absolute minimum sample rate is twice the bandwidth of the oscilloscope to avoid aliasing.
How Do You Calculate Bandwidth From the Sample Rate
Bandwidth cannot be accurately calculated from the sample rate, but an approximation of the bandwidth can be made. According to Physicist Harry Nyquist, bandwidth must be less than half of the sample rate. But practically, it is generally one-fifth of the sample rate to enhance accuracy.
Why Is Bandwidth Important on an Oscilloscope
Bandwidth is the range of operation of an oscilloscope. For accurate measurements, bandwidth must be more than the highest frequency component of the signal to avoid attenuation of the signal. But it also must not be too large than the input signal frequency to introduce noise in the output.
Frequently Asked Questions
What is more important between bandwidth and sample rate?
Bandwidth is the most important feature of an oscilloscope. Because bandwidth is the operating range of the oscilloscope. The limit of operation of an oscilloscope is defined by its bandwidth.
Conclusion
Bandwidth and sample rate are the most important factors to take into consideration while buying or choosing an oscilloscope for a specific task. Between bandwidth and sample rate, the effect of bandwidth is more vital to the accuracy of the oscilloscope.
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Hello Charles,
I have a question. For Agilent 54610B, bandwidth is 500Mhz but sample rate is 20MSa/s.
I cannot understand why sampling rate will be less than bandwidth.
The Agilent 54610B 2 Channel oscilloscope has a bandwidth of 500 MHz, which means it can accurately measure signals up to a frequency of 500 MHz. However, the sample rate of 20 MSa/s (mega-samples per second) means that the oscilloscope can only capture up to 20 million samples per second.
The Nyquist-Shannon sampling theorem states that in order to accurately reconstruct a signal, the sampling rate must be at least twice the highest frequency component of the signal. Therefore, in the case of the Agilent 54610B oscilloscope, it can accurately capture signals up to half its bandwidth, which is 250 MHz.