Understanding Oscilloscope Bandwidth, Rise （了解示波器带宽,增加）.pdf

Technical Brief Understanding Oscilloscope Bandwidth, Rise Time and Signal Fidelity Introduction When an oscilloscope user chooses an oscilloscope for making critical measurements, banner specifications are often the only criterion used to make this choice. The top three oscilloscope banner specification categories are: • Bandwidth • Sample Rate • Record Length And of these banner specification categories, the number one asked for capability in an oscilloscope is bandwidth. After all, more bandwidth means higher performance, right? Well, not necessarily. This article will point out the pitfalls in this very simple assumption. Depending upon your expectation to see and analyze signals as they really are, more knowledge about the true performance of your oscilloscope will be needed. 1 Technical Brief BANDWIDTH – WHAT DOES THIS SPECIFICATION TELL US? Bandwidth is a sine wave specification that simply defines the frequency at which the peak-to-peak amplitude of the sine wave on the screen is down by 3 dB from the actual sine wave amplitude. Figure 1 shows an idealized sine wave amplitude roll off error as the signal approaches the oscilloscope bandwidth frequency. At the rated bandwidth, the percent of error on screen is 29.3%! 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 100.0 } 3% 97.5 95.0 92.5 90