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Simulators >> RF Simulators >> conversion gain of mixer
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Message started by manfred on Jan 5^th, 2008, 3:30am

Title: conversion gain of mixer
Post by manfred on Jan 5^th, 2008, 3:30am

Hi, everyone!

when I simulate the conversion gain of mixer, I can choose PXF or PSP. but the result is different.
I think the result of PXF is voltage gain, and the result from S21 of PSP is power gain, Is it right?

also, the load of mixer is resistor, when I run the simulation, I add the PORT between the differential output, but how to set the resistor value of the PORT?
50ohm or other values? when I change the resistor value of the PORT, the conversion gain from PXF and S21 are both changed.
so, in order to get the right conversion gain result , what value of the resistor in PORT should I set ?

thanks a lot!

Title: Re: conversion gain of mixer
Post by didac on Jan 5^th, 2008, 4:44am

Hi,
You are right that PXF result is voltage gain, s21 is Transducer Gain not directly Power Gain. The value of the resistor of the port should be the input impedance of your next stage to make a measurement of Voltage Gain.
Hope it helps,

Title: Re: conversion gain of mixer
Post by manfred on Jan 6^th, 2008, 3:39am

thanks didac for the reply!

I have two problem about my question as follows:

1. I wonder about Transducer Gain in your answer, what is it? and what relation with Power Gain is it?
2. about PORT, if the output of mixer is connected to the gate of next stage, should I set the resistor of PORT as large as possible?
or else, if the resistor of PORT is comparable to the load of mixer, the conversion gain of simulation is not true, is it right? is it load effect?

any reply would be appreciated!
thanks a lot!

Title: Re: conversion gain of mixer
Post by didac on Jan 6^th, 2008, 8:28am

Hi manfred,
1.This will be quite teoric since it comes all from microwave theory and how spectreRF implements it:
In general you have several "Power Gains"
Transducer Power Gain(unilateral-->s12=0):
G_TU=((1-abs(Γs)^2)/abs(1-s11*Γs)^2)*abs(s21)^2**((1-abs(Γl)^2)/abs(1-Γout*Γl)^2)
Where:
Γs:source reflection coefficient,Γl=load reflection coefficient,Γout=output reflection coefficient.
Since spectreRF uses as reference impedance of each port the port impedance Γs=Γl=0 and G_TU=abs(s21)^2,this gain is the ratio between power delivered to the load and power AVAILABLE from the source(input impedance conjugated matched to the source, if the source impedance it's 50 ohms and you matched to 50 ohms the it makes sense as power gain).
There are several definitions of power gain a good book that has all the definitions it's "Microwave Engineering" of David M. Pozar, Wiley Editorial.
2)Yap you are completely right, if you put a port impedance of the same order of magnitude you are loading the mixer.
Hope it helps,

Title: Re: conversion gain of mixer
Post by manfred on Jan 7^th, 2008, 1:56am

thank you very much, didac!

your detailed answers are very helpful for me!