eecs4ever wrote on Nov 20th, 2009, 10:28am:The definition for noise figure is SNRin/SNRout assuming an input noise floor of kTB (typically -174dBc/Hz).
For an amplifier, the output noise floor is raised by the amplifier gain plus the noise figure in dB.
Does this hold for a mixer as well?
Yes, if B=1Hz although you have typo.
But you have to consider "Spurious Response Frequencies" for RF inputs.
For example, Half-IF, SSB(USB, LSB) and DSB.
Again see http://www.designers-guide.org/Forum/YaBB.pl?num=1239925339eecs4ever wrote on Nov 20th, 2009, 10:28am:For the two inputs, I meant the RF and LO.
Is the noise folding different
if the RF and LO are the same frequency and we are mixing down to baseband as oppose to an IF?
Both for zero-IF and non-zero-IF, they are different.
eecs4ever wrote on Nov 20th, 2009, 10:28am:If these are different, is there a separate noise figure for each case?
Also are we assuming that the input noise floor is only applied at the RF signal
and the LO signal is pure when taking the noise figure of the mixer?
Generally we don't define NF for LO input.
Noise effect from LO is also included in NF for RF Port. Here noise folding from LO is also included.
Consider
Numerator and Denominator of NF definition.
Most important things of NF for Mixer is that there are many RF frequencies which yield same IF frequency.
These frequencies are called as "Image Frequencies" or "Spurious Response Frequencies".
Again see http://edocs.soco.agilent.com/display/ads2009/Harmonic+Balance+for+Mixers
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questions about noise figure for mixers (Read 4512 times)