https://haifei.pro/en/tags/signal-integrity/Recent content in Signal Integrity on Haifei's HomeHugoenhfwang132@gmail.com (hfwang132)hfwang132@gmail.com (hfwang132)This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.Sat, 25 Oct 2025 16:46:08 +0800https://haifei.pro/en/post_20251025_%E9%98%BB%E6%8A%97%E5%8C%B9%E9%85%8D-%E4%BF%A1%E5%8F%B7%E5%AE%8C%E6%95%B4%E6%80%A7%E9%80%9F%E6%88%90-%E5%AE%9E%E9%AA%8C%E5%AE%A4%E7%89%88/Sat, 25 Oct 2025 16:46:08 +0800hfwang132@gmail.com (hfwang132)https://haifei.pro/en/post_20251025_%E9%98%BB%E6%8A%97%E5%8C%B9%E9%85%8D-%E4%BF%A1%E5%8F%B7%E5%AE%8C%E6%95%B4%E6%80%A7%E9%80%9F%E6%88%90-%E5%AE%9E%E9%AA%8C%E5%AE%A4%E7%89%88/<h2 id="i-introduction">I. Introduction</h2> <p>Recently, I found that many colleagues are not very familiar with impedance matching. They only know that “the impedance of (commonly used SMA/BNC) transmission lines is 50 ohms,” but do not know what this really means. The following situations often occur:</p> <ul> <li>A 50-ohm signal source connected to a scope with a 1M-ohm input:</li> </ul> <ul> <li>Huh, why did the signal become twice as large?</li> </ul> <ul> <li>A high-frequency square wave connected to a scope with a 1M-ohm input:</li> </ul> <ul> <li>Huh, why is the overshoot so severe? Is there something wrong with this signal source?</li> </ul> <ul> <li>The output signal of an MCU / DAC / FPGA connected directly, without a driver, to a 50-ohm load / 50-ohm oscilloscope input:</li> </ul> <ul> <li>Huh, why did a signal that was supposed to be 3V become only 30 mV?</li> </ul> <p>All of the above result from unfamiliarity with impedance matching and transmission-line theory.</p>