My chip has a measured LO leakage at the mixer IF output. It is in worst case only 25dB lower than the desireable IF signal. what could be the reasons and what is the bad side of this leakage?
My chip has a measured LO leakage at the mixer IF output. It is in worst case only 25dB lower than the desireable IF signal. what could be the reasons and what is the bad side of this leakage?
yes, the chip has a low pass filter after the mixer. My concern is what kind of issue the big LO leakage could have though it can be filtered out after the mixer.
yes, the chip has a low pass filter after the mixer. My concern is what kind of issue the big LO leakage could have though it can be filtered out after the mixer.
Got it.
If the LO is far away from IF, it can be filtered easily, but if they are very close, the LPF will be difficult to realized.
So, I think if LO is close to IF, we should use the double balance MIX.
When there is poor isolation between LO and IF circuits noise from LO will go to IF and compromise the signal to noise ratio. Also LO signals may interact with IF signals and create unwanted products. But this is the task of frequency planning to avoid such problem.
When there is poor isolation between LO and IF circuits noise from LO will go to IF and compromise the signal to noise ratio. Also LO signals may interact with IF signals and create unwanted products. But this is the task of frequency planning to avoid such problem.
Yes, LO will interact with IF Signals, but if the frequency of LO is thousands times of frequency of IF,
does it also interact with IF, and is the effect serious?
The effect depends on frequency plan and design. If frequency planning and physical implementation were done right system performance should met the spec. This is designer's work to do so.
Just one simple situation from real life: due to layout imperfections and wrong LO filter type the S32 for mixer were low and odd harmonics of LO had almost no attenuation. As results system sensitivity was compromised and design started from scratch.
There is a lot of tools for frequency planning. usually they are based ob so called spur charts. I usually use my own and redesign them if it necessary to accommodate to particular need. You may check www.rfcafe.com. There was one good tool.