What's a good value of P1dB and IP3 of a mixer?

what's a good value of P1dB and IP3 of a mixer ? or depends on the application ?

appcad noisecalc example

It depends from the application, but obviously, higher P1dB and highe IP3 means higher linearity.


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diode mixer ip3

thanks, and what about the different applications ? you know some references where I can check what value of P1dB and IP3 are good enough ?

mixer what iip3 means

higher P1dB and highe IP3 is ok,of course which value is enough?It is the project what you need.

high ip3 mixer diodes

It is the project that have to drive the choice of a mixer with a certain linearity carachteristic.
When i say project i mean the whole project and the evaluation includes cost, how easy you can find it, if it is best to design it or to buy it...

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p1db rf terminology ip3

all project specific questions

im3 + p1db

Hi

there are some known-good topologies and some guidelines could be given in general.

Diode mixers are very linear and simple to build. The trade-offs with diode mixers are in chosing a diode for the application. Low barrier Schotky diodes require less LO pumping power to achive low conversion loss, but they are most nonlinear. High barier diods are most linear but LO pumping power is higher. Medium barier are somwhere in between.

FET resistive mixer could achieve almost linear operation, the transistor is operating in so called triode - linear region. Conversion loss is in line with diode mixers.

FET gate mixers could have significant conversion gain, but they will be most nonlinear comparing with other two.

Hope this helps. Much more details are available from the book Microwave Mixers from Steve Mass

flyhigh

iip3 and triode region

so if P1dB and IP3 depends on the application of the whole system, would someone have an example of these requirements, for example for GSM or other protocols

Re: P1dB and IP3 mixer

some example on P1dB and IP3 for some application ??

Thanks!

Re: P1dB and IP3 mixer

Hi,

Typical requirements of ETS300-086 Standard for a VHF or UHF mobile radio's receiver:
(1) sensitivity of -113dBm (0dBuV EMF) at 10dB S/N;
(2) Third order Intermodulation Distortion of -70dB min ( with 2 interfering signals detuned +25kHz and +50kHz (and/or -25 and -50kHz) from the receiver's nominal frequency Fin.)

With these interfering signals the frequency of one of the worst case IM3 products is, Fim3= 2*(Fin+25)-(Fin+50)=Fin, exactly on the receiver nominal frequency.

Let suppose we have an ideal (lossless and linear) RF filter before the mixer and no RF amplifier. Let say also, the sensitivity of the receiver is at the required Pmin=-113dBm, the receiver tract after the mixer is ideal too (noiseless and absolutely linear). So, we need our mixer alone to meet requirement above.

Let see, what the requirement of ETS300-086 means:
Our mixer, whith two interfering signals applied, each 70dB larger than nominal sensitivity (or Pin= -43dBm), must generate IM3 prodicts at the noise level of the receiver, which is Pn= Pmin - SN= -113dBm - 10dB = -123dBm. Or IM3's of the mixer must be at least IM3= Pin-Pn= -43 -(-123)=80dB, to meet the requirement. It means the required minimum input IP3 of our mixer must be equal to:

IP3=0.5*IM3+Pin= 0.5*80+(-43)=-3dBm. (A)

As you can see in the equation (A) , the noise level is not present. It means, the IM3 and IP3 can be measured without knowing the noise factor. We need to apply two signals with equal (reasonably low) amplitude and look at the level of generated IM3 products and calculate then IP3.

Of cource, in a real receiver, you probably will have an RF amplifier and a filter before the mixer, so you must know the gain from the antenna to the mixer input, the noise factor of the receiver, taken on the mixer input and the noise factor of cascaded RF amplifier and filter to make proper calculations.

In any case, everything is system dependand. Standard requirements and published data of the products, similar to yours design, are a good start point. There is no universal receipt, you must make some compromises in every project - an oversized in terms of IP3 system will be more expensive and probably more power hungry. The initial system level design is very important - it must be made carefully. Errors or wrong decisions made on the initial system level design usually are not easy to be corrected in later stages of the design.

You may downoad Agilent AppCAD and play a litle bit the NoiseCalc inside.


Best Regards,
S.