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TRF372017: TRF372017 Upper Side Band or Lower Side Band Derivation with Respect to the Local Oscillator

Kang Hsia
Guru 66044 points
Part Number: TRF372017
Other Parts Discussed in Thread: TRF3722

Dear E2E,

We are seeing some frequency inversion when we feed the DAC I_output to the TRF I_input, and DAC Q_output to TRF Q_input.  Is this expected? 

My analysis shows that this is the case when the LO is sine (which resulted in frequency inversion at the output of the IQ modulator).  When the LO is negative sine, then the output frequency is not inverted.  We are trying to troubleshoot to see if there is a bug in the FPGA.LO as positive Sine is LSB.pdf

LO as negative Sine is USB.pdf

  • 0
    TI__Guru 66044 points

    Hi,

    This is within expectation. 

    The general complex I/Q (quadrature) modulation have the following equation:

    You may notice the signal is upper side band modulation when the carrier has a negative sine, and it is lower side band modulation when the carrier has a positive sign.

    Another way to derive this is through the use of signum property at the frequency domain level

  • 0
    Prodigy 30 points

    My question is whether the LO inside the TRF372017 is positive sine for the Q mixer.  I and Q were not swapped and this resulted in frequency inversion at the output of the TRF372017 based on our IQ configuration in the FPGA.  It would be great if someone can also confirm that if I and Q are not swapped, the output is LSB.

    Thanks,
    Peter.

  • +1 in reply to Peter Hoang
    TI__Mastermind 18065 points

    Peter:

    One of the BB input p/n pins is swapped in the device, so what you are seeing with the LSB operation is expected.  This was done for die layout routing and was not  corrected in the documentation in an effort not to confuse existing-use customers.  Unfortunately, it is confusing for new customers.  Fortunately, it is easy to swap the p/n as needed to get desired sideband in the DAC or in the FPGA pattern.

    If you are not already familiar, the TRF3722 is an updated modulator with integrated PLL/VCO.  The TRF3722 supports a higher linearity modulator and a slightly better phase noise PLL/VCO.

    --RJH