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TRF371125: IQ amplitude imbalance/influence of ILOAD/QLOAD registers

Max Koeppel
Prodigy 80 points
Other Parts Discussed in Thread: TRF371125

Dear Sir or Madame,

I am using the TRF371125 IQ demodulator for a SDR frontend. Therefore the I/Q signals are fed into two seperate ADCs and sampled. Unfortunately, I discovered effects of IQ imbalance. Since the two signal pathes are exactly the same length (I payed attention to this when I was doing the layout), I don't think that I have a phase imbalance issue. I rather think that the different magnitudes of the I and Q signal are the reason for the effects I discovered (see attached FFT plot of a sine signal).

I investigated the datasheet of the TRF371125 and discovered the registers "ILOAD_A", "ILOAD_B", "QLOAD_A" and "QLOAD_B". In the datasheet there is only stated: "I/Q Mixer Load A/B: these bits adjust the load on the mixer output. All values should be 0. No modification is necessary."

But may these registers help to mitigate the amplitude imbalance? How do they affect the operation of the TRF371125? And are there any other registers I should modify?

Thanks!

Best Regards,

Max