What is the difference between spectrum analyzer and oscilloscope?
In the groups of spectrum analyzer, including college teachers, research and development engineers, production test engineers and so on.The two most frequently asked questions are: what is the difference between oscilloscope and spectrum analyzer? When should we use a spectrum analyzer?
The spectrum analyzer is one of the most basic and commonly used instruments in the rf field, and so many people are unfamiliar with its basic concepts and USES.
The common oscilloscope on the market is with the function of spectrum display, this is mainly the use of Fourier transform (FFT) to carry out the time domain and frequency domain conversion, but what are the difference between the oscilloscope FFT and spectrum analyzer in the radio frequency test application?
1.Apply to different types of signals, the oscilloscope is mainly used to observe the time-domain characteristics of the signal (that is, the voltage changing with time), mainly applicable to the analysis of baseband signals (sinusoidal wave, square wave, bitstream and other unmodulated signals). Spectrum analyzers, on the other hand, focus on rf signals (especially complex signals with modulation or multi-frequency signals that show little or no pattern on the timeline). Although an oscilloscope can also display signals from the perspective of frequency domain through FFT, its performance index is generally insufficient to analyze rf signals with modulation.
2.The bandwidth of the measurement are different. Oscilloscope design is mainly used to observe baseband signals, so generally speaking the bandwidth is not very wide, the most common is dozens to hundreds of MHz. Of course, with the rapid development of digital circuit technology, the speed of baseband signal is also increasing rapidly, so some high-end oscilloscopes can also reach the GHz order of magnitude. And spectrum analyzer is mainly used to analyze carrier and modulated rf signal, so spectrum analyzer frequency range is usually much wider.
3.The measurements vary: oscilloscopes observe voltage changes over time, so they typically see sinusoidal, square, bit-current, focusing on voltage, period, rising and falling edges, overshot, burrs, and timing between multiple signals. The spectrum analyzer looks at rf signal power, frequency, distortion (harmonic and intermodulation products), modulated bandwidth, size of leakage to adjacent channels, noise testing, and in-depth analysis of complex modulation signals (modulation regimes, IQ constellations, modulation errors, etc.)
4.Different sensitivity, oscilloscope seen were baseband signal and through conduction mode connection, signal amplitude are generally stronger, in a few volts, 10 points a few or a few percent v power in milliwatts (level), and the spectrum analyzer often need to measure the emission spectrum or rf signal received from the air, the low power tend to be more than one milliwatt several even ten several ten times, even lower conversion to a few microvolts.
5.Different dynamic range, dynamic range refers to the ability to observe both large and small signals. When an oscilloscope is observing a signal with a main signal scale at the volt level, it is convenient to observe the subtle signal or wave at the zero or zero volts. That means a resolution of one tenth or a few hundredths of the voltage (one hundredth or a few tenths of the power). A spectrum analyzer can simultaneously observe small signals that are one millionth, one millionth, and one millionth of the power of large signals. In the field of rf measurement, such a large dynamic range is often needed.
1.The focus is on rf devices and rf signal testing (carrier and modulated signals), such as testing rf transceivers.
2.Check for unknown signals in broadband, such as the composition of air signals and various rf interference, EMC test of electronic products, etc
3.Focus on both large and small signals, such as the transmitter's signal distortion, intermodulation, clutter, etc.
4.Focus on weak signals below millivolts, such as the coupling between signals on printed circuit boards, stray clutter on power supplies and clocks, etc.
The first three applications are typical applications of spectrum analyzers, while the fourth is not familiar to engineers and is often the biggest headache for circuit design engineers.Most of the time, engineers only consider this when they find problems with the whole machine in the later stage of development.