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https://designers-guide.org/forum/YaBB.pl Design >> RF Design >> source voltage https://designers-guide.org/forum/YaBB.pl?num=1662033568 Message started by Marios on Sep 1st, 2022, 4:59am |
Title: source voltage Post by Marios on Sep 1st, 2022, 4:59am Dear all, I have a general question with regards to the PORT instance found in analogLib of cadence. At AC magnitude section of the PORT I set a unit magnitude. Then the port internally will have a magnitude of 2. Initially I thought that this "doubling" of magnitude is performed internally so that the port behaves as a transmission line and take care of the effect of impedance mismatch. Asking around I was then told that the "doubling" is so that when I calculate voltage gain (say I drive an LNA with that port), I present my LNA with unit magnitude at its input. So my question is this. Does that mean that a real antenna that has an internal resistance of 50 ohms, delivers a unit magnitude to an LNA? In other words, the open circuit voltage of the antenna has a magnitude of 2? Because if not, then there is a discrepancy between how I model my circuit and the reality. Thanks in advance Marios |
Title: Re: source voltage Post by Ken Kundert on Sep 1st, 2022, 4:20pm Your transmission line explanation is correct. Your colleagues explanation is a bit off: they are explaining why you specify the port voltage magnitude to be unity, not why there is a doubling from the specified value to the internal drive voltage. Basically, when you specify the port voltage, you are specifying the that will result when the port is loaded with a matched load. This is the exactly the same thing you do when you specify the voltage on a high-frequency signal generator. If you connect an hp8640 signal generator to an oscilloscope and set it to deliver 1Vp, you will see a 2Vp signal on your oscilloscope until you remember to enable the 50Ω terminating resistor on the scope, at which point you see a 1Vp signal. The same would be true from a 1Vp signal coming from an antenna. |
Title: Re: source voltage Post by Marios on Sep 5th, 2022, 2:44am Ok thank you for your detailed answer! Marios |
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