IMD asymmetry

[Leiser]

Hello,

I am measuring IMR3 of a DAB band III LNA from production. Some boards show IMR3 asymmetry and others not. Does anyone know what could be the cause? The LNA is implemented by a MIMIC MGA-62563.

Also the IMR3 has drop for the case of asymmetry.

I attach the two plots.

 

[VEBill]

One old trick is to add some attenuation (e.g. -6dB) between the UUT and the measuring instrument (the spectrum analyzer side, *not* the signal generator side). This can help to ensure that the line is 'flat', and confirm that your measured ratios are stable (real measurements, not artifacts).

 

[Leiser]

Thanks very much for you prompt answer.

I tried but didn't work. It seems some ESD protection diodes from different batches are responsible for the IMR asymmetry. I changed them and it work.

 

[VEBill]

Excellent. Congratulations on figuring it out so fast.