Hi
We are using  a standard NF meter to measure the NF of our ZIF reciever IC { 5GHz to analog BB }in the Lab.
Thus we can measyre from LNA in to either I or Q out {but not both simultaneously }
So my question isif the measured NF reading is 5dB does this mean the overall "Receiver NF" is 2dB or
how do we account for the un measured quadrature channel ?

Thanks


DBRF1

Jess thanks for the reply
A few questions to double the signal you assume we shift the I {or Q by } by 90 degs then we can add 2 signals in phase hence get 6dB increase in voltage.
Does the same apply to the noise  . Doesn't it depend if there is a noise contribution from the mixers thus the I noise will not be totally correlated with the
Q noise so it is not true to say that the noise on the I branch is in Quadrature with the noise on the I branch ??/

Also wrt the DSB/SSB NF comments.  My understanding was that for a ZIF rx there is NO image band  so in fact for this type of receiver the DSB and SSB NF are the same as ther is in fact only one Signal band  .   { Image = Wanted +/- 2*IF   , IF = 0  thus image = wanted  }  ??

DBRF1

In ZIF recievers I have worked on (for GSM/EDGE) we always measured noise figure on I or Q (the results being the same). This is what we quoted on datasheets/what the baseband DSP guys wanted.

DBRF1 wrote on Nov 21^st, 2006, 11:41am:


I agree with Jess's comments, i have measured the NF of a ZIF transciever in two ways:
1) C/N method: Using a CW carrier one side of the LO, so had to adjust the NF by -3dB to account for the fact the modulated input signal would occupy both sides (the noise was both side of the LO... its a bit diffcult for it not to be).
2) Measuemnt with noise diode (Y-factor method) gives the same result... without the need for the 3dB adjustment.

The treatment of this in Razavi's "RF Microelectronics" p183 is quite good, and aglient do a good app note on y-factor noise measurement.


DBRF1 wrote on Nov 21^st, 2006, 11:41am:


I used to think of it as adding signal I and Q in vector form, so you add as squares (I^2+Q^2)....  noise also adds as squares... not sure if my loose thinking is strictly correct but i managed to convince myself quite easily  ;)
Best way to convince yourself is if you have a dual channel VSA (Vector signal analyser) like HP89441 or R&S FSIQ... then you can measure NF on I or Q using C/N method with -3dB correction factor, and then put the VSA in I+jQ demodulation mode to see it give you the same/similar NF or C/N.


cheers
aw

Maybe you meant (I have not worked out the maths) ZIF demodulator/mixer, but put a LNA with NF<3dB and infinite gain in front of your ZIF mixer/demodulator, you get receiver NF<3dB.

I have used 'similar' approaches described by ACCWong, except that I have not measured the NF on I or Q channels only, always I+jQ.