Feed a two tone signal (f ~1~ and f ~2~ ) to a nonlinear system, the following distortion product would be generated:
h6. 2 ^nd^ order
f ~1~ + f ~2~
2f ~1~
2f ~2~
f ~2~ - f ~1~
...
h6. 3 ^rd^ order
2f ~2~ - f ~1~
2f ~1~ - f ~2~
...
My questions are:
1. MXA/PXA specifies the 2nd order harmonics distortion, but what about the 2nd order IMD f ~1~ + f ~2~ ?
2. Which part of the signal chain contribute the most to the 2nd order IMDs, including f ~1~ + f ~2~, 2f ~1~ and 2f ~2~ ? Is it the mixer, the IF amplifier, the ADC or something else?
h6. 2 ^nd^ order
f ~1~ + f ~2~
2f ~1~
2f ~2~
f ~2~ - f ~1~
...
h6. 3 ^rd^ order
2f ~2~ - f ~1~
2f ~1~ - f ~2~
...
My questions are:
1. MXA/PXA specifies the 2nd order harmonics distortion, but what about the 2nd order IMD f ~1~ + f ~2~ ?
2. Which part of the signal chain contribute the most to the 2nd order IMDs, including f ~1~ + f ~2~, 2f ~1~ and 2f ~2~ ? Is it the mixer, the IF amplifier, the ADC or something else?
> 1. MXA/PXA specifies the 2nd order harmonics distortion, but what about the 2nd order IMD f ~1~ + f ~2~ ?
> 2. Which part of the signal chain contribute the most to the 2nd order IMDs, including f ~1~ + f ~2~, 2f ~1~ and 2f ~2~ ? Is it the mixer, the IF amplifier, the ADC or something else?
1) I've not seen it spec but you might expect two-tone SOI to be about 6 dB worse than SHI as for the same input signal (two tones at the same power relative to one tone for harmonics) the SOI has 6 dB higher peak power. BUT! in the portion of the band with a pre-selector, the SOI and SHI will be very high as the preselector tuned to the second harmonic will isolate the fundamental from the mixer. In PXA this occurs when the second order signal is about 3.6 GHz (fundamental above 1.8 GHz).
2)Usually it is the first mixer, the reason being it is high frequency and lower freq components can be more readily optimized for better peformance, but in the PXA the IF is optimized to actually improve the raw mixer response so it is the whole chain that contributes.