Difference between oscilloscope and spectrum analyzer

The common oscilloscopes on the market have the function of spectrum display , This is mainly the use of Fourier transform （FFT） To convert time domain and frequency domain , But the oscilloscope FFT And spectrum analyzer in RF test application ？

1. The applicable signal types are different ： The oscilloscope is mainly used to observe the time-domain characteristics of signals （ That is, the transformation characteristics of voltage with time ）, It is mainly applicable to baseband signal analysis （ Sine wave , square wave , Unmodulated signals such as bitstreams ）, The spectrum analyzer is mainly used for RF signals （ In particular, complex signals or multi frequency signals with modulation , Such signals hardly show any regularity on the time axis ） Analysis of . Although the oscilloscope can also pass FFT Display the signal from the angle of frequency domain , However, its performance index is generally not enough to analyze the RF performance , Signal with modulation .

2. The measured bandwidth is different ： The design of oscilloscope is mainly used to observe baseband signal , So generally speaking, the bandwidth is not very wide , The most common are dozens to hundreds MHz. Of course , With the rapid development of digital circuit technology , The rate of baseband signal is also increasing rapidly , therefore , Some medium and high-end oscilloscopes can also reach GHz This order of magnitude . The spectrum analyzer is mainly used to analyze the carrier wave and modulated RF signal , Therefore, the frequency range of the spectrum analyzer is usually much wider

3. The measurement contents are different ： The oscilloscope observes the change of voltage with time , So what you usually see is a sine wave , square wave , Bit stream, etc , Pay attention to the voltage , cycle , rising , Falling edge , Overshoot , skin needling , And the time sequence between multiple signals . The spectrum analyzer looks at the power of the RF signal , frequency , The distortion （ Harmonic and intermodulation products ）, Modulated bandwidth , The size of leakage to adjacent channels , Noise test , And the in-depth analysis of complex modulated signals （ Adjust the system ,IQ Constellations , Modulation error, etc ）

4. Different sensitivity ： The oscilloscope looks at baseband signals and connects them through conduction , The signal amplitude is generally strong , At a few volts , A few tenths or hundredths of a volt （ The power is in the milliwatt level ）, The spectrum analyzer often needs to measure the spectrum of the transmitted signal or the RF signal received from the air , Power tends to be higher than 1 Milliwatts are still a few or even a dozen times the power of ten , That translates to a few microvolts or less .

5. Different dynamic ranges ： The so-called dynamic range , It refers to the ability to observe large signals and small signals at the same time . When the oscilloscope is observing a signal whose main signal scale is at the volt level , The subtle signal or fluctuation that can be easily observed is in the zeros or zeros of a few volts . That is to say, the resolution of the voltage is 10% or a few% （ A few percent or ten thousandths of the power ）. The small signal that the spectrum analyzer can observe at the same time can be one millionth of the power of the large signal , One in ten million , One in 100 million . In the field of RF measurement , Such a large dynamic range is often required .

1. Focus on RF equipment and RF signal testing （ Carrier and modulated signal ）, For example, test the RF transceiver

2. Check the unknown signal in the wide band , For example, the components of air signals and various radio-frequency interferences , Of electronic products EMC Testing, etc

3. Focus on both big and small signals , For example, I want to know the distortion of the transmitter signal , Intermodulation , Clutter, etc .

4. Pay attention to weak signals below the millivolt level , For example, pay attention to the coupling between signals on the printed circuit board , Spurious clutter on power supply and clock .