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https://designers-guide.org/forum/YaBB.pl Design >> RF Design >> Is S21 the actual gain of a LNA?? https://designers-guide.org/forum/YaBB.pl?num=1215827287 Message started by zhangjerome on Jul 11th, 2008, 6:48pm |
Title: Is S21 the actual gain of a LNA?? Post by zhangjerome on Jul 11th, 2008, 6:48pm There are three kinds of gain, power gain, transuducer gain, availble gain. Which one is the gain we concern?? In Spectre, with a 50 ohm port as the input, is S21 the gain of the LNA even the input is not well matched?? |
Title: Re: Is S21 the actual gain of a LNA?? Post by pancho_hideboo on Jul 11th, 2008, 10:38pm zhangjerome wrote on Jul 11th, 2008, 6:48pm:
S21 is a transducer gain. You have to learn measurements using actual instruments. Not "EDA Tool Play". |
Title: Re: Is S21 the actual gain of a LNA?? Post by zhangjerome on Jul 13th, 2008, 4:23am H, Pancho. As I know, the transducer gain is a function of S21 and other parameters, such as source and load reflection coefficients. Why do you think S21 is the transducer gain?? |
Title: Re: Is S21 the actual gain of a LNA?? Post by pancho_hideboo on Jul 13th, 2008, 7:26am zhangjerome wrote on Jul 13th, 2008, 4:23am:
All incomplete knowledges are always useless. You don't seem understand basic of RF. But this is not restricted to you. 1/S21 is a insertion loss. Definition of insertion loss is same as inverse of sqrt(transducer gain). See circuit theory text book, especially on filter design. http://en.wikipedia.org/wiki/Power_gain If you think the following, you must consider reference impedance of S-parameters definition. In the following, what values are used as reference impedances(Z01 and Z02) of S11, S12, S21, S22 ? http://www.maurymw.com/support/faqs/faqs/faq9.html Gamma_S=(ZS-conj(Z01))/(ZS+Z01), ZS is source impedance. Gamma_L=(ZL-conj(Z02))/(ZL+Z02), ZL is load impedance. If Z01=conj(ZS), Gamma_S=0. If Z02=conj(ZL), Gamma_L=0. Here these are not matching. So S21=sqrt(Transduder Power Gain) is satisfied. Usually ZS and ZL are real impedances such as 50ohm. Again You have to learn measurements using actual instruments. Not "EDA Tool Play". |
Title: Re: Is S21 the actual gain of a LNA?? Post by zhangjerome on Jul 13th, 2008, 6:21pm Hi, pancho. Thank you for you patience. Seems I get it. Both gamma_source and gamma_load are zero. So S21 is actully equal to transducer gain. Am I right? |
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