How he came up with this is an untold story, but he provided a solution to the complex calculations on transmission lines. The intimidating graph, developed by Philip Smith in 1939, is just about as bad as it looks. Most of you have probably heard of the Smith chart. Identify impedance-matching component values from the Smith chart.Determine the impedance of a load at the end of a transmission line.Plot complex impedances on a Smith chart.Members can download this article in PDF format. If you do not allow these cookies, you will experience reduced relevant content.This article is part of the Analog Series: Back to Basics: Impedance Matching They do not store directly personal information, but are based on uniquely identifying your browser and internet device. They may be used by Analog Devices to build a profile of your interests and show you relevant content on our site. Targeting Cookies: These cookies may be set through our site by Analog Devices and our service providers. If you do not allow these cookies we will not know when you have visited our site, and will not be able to monitor its performance. All information these cookies collect is aggregated and therefore anonymous. They help us to know which pages are the most and least popular and see how visitors move around the site. Performance Cookies: These cookies allow us to count visits and traffic sources so we can measure and improve the performance of our site. If you do not allow these cookies then some or all of these services may not function properly. They may be set by us or by third party providers whose services we have added to our pages. Functional Cookies: These cookies enable the website to provide enhanced functionality and personalization. These cookies do not store any personally identifiable information. You can set your browser to block or alert you about these cookies, but some parts of the site will not then work. They are usually only set in response to actions made by you which amount to a request for services, such as setting your privacy preferences, logging in or filling in forms. Strictly Necessary Cookies: (Always Active) These cookies are necessary for the website to function and cannot be switched off in our systems. After we finish updating our website, you will be able to set your cookie preferences. Finding these component values can be done using computer simulations, manual computations, or with tools such as the Smith chart.Īnalog Devices is in the process of updating our website. Matching networks are configurations used to match source and load impedances, and impedance matching devices are the components that make up these networks. Impedance matching will result in both minimal signal reflection and maximal power transfer in DC systems. Since reactance is zero in DC systems, this is equivalent to the two resistances being the same in either case. Minimal signal reflection is obtained when the source impedance is equal to the load impedance (Z S=R L+jX L), which is called reflectionless matching. Maximum power transfer is obtained when the output impedance of the source is equal to the complex conjugate of the input impedance of the load (Z S=R L-jX L). reflectionless matchingĭepending on whether the goal of impedance matching is maximizing power transfer or minimizing signal refection, either conjugate matching or reflectionless matching is required. Impedance matching is therefore important to obtain a desirable VSWR (voltage standing wave ratio). These reflections cause destructive interference, leading to peaks and valleys in the voltage. Impedance mismatch can lead to signal reflection and inefficient power transfer. In DC systems, the reactance is zero, so the impedance is the same as the resistance. The equation for impedance is then by definition Z=R+jX, where j is the imaginary unit. Impedance (Z) is a measure of the opposition to electrical flow, which is a complex value with the real part being defined as the resistance (R), and the imaginary part is called the reactance (X). In AC circuits, the source should either equal the load or the complex conjugate of the load, depending on the goal. In DC circuits, the source and load should be equal. Impedance matching is designing source and load impedances to minimize signal reflection or maximize power transfer.
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