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Part Number: TRF370417
I am using TRF370417 quadrature modulator to modulate two sets of IQ balance signals into one unbalance signal.
The two sets of IQ signal frequency = 245.76MHz.
LO frequency = 2686.76MHz.
The output signal frequency should be 2441MHz.
The two sets of input signals are comb spectrum signals which have 80MHz.The flatnesses of input signals are good which are 1dB flatness.
The output of TRF370417 flatness has degraded. Highest and lowest comb-fingers amplitude difference is about 13dB.
Please refer to pictures below.
Could kindly help to give me some suggestions?
I think there are 3 possibilities for this issue: RF output ripple, BB ripple, or S/A resolution.
For the RF output, the device is sensitive to load impedance. The device needs/wants to be terminated in a good, broadband 50 ohm load. Connecting a long cable from RF output to S/A may introduce reflections that cause a lot of output ripple. Try to add a 6-10 pad right on the EVM RF output SMA connector and use a good quality RF cable to see if the performance improves.
For the BB ripple, the IF looks to be 245.76 MHz. That is a fairly high IF frequency. As an experiment, try to move the IF down to something like 60 MHz and adjust the LO accordingly to keep the same RF output. See if there is any significant change in the ripple performance. Also insure that the Vcm at the modulator is truly 1.7V on all 4 ports.
Just to be sure the S/A is not tricking you, adjust the ResBW higher. With a large sweep bandwidth, I have seen cases where the peak of the comb signal is not always caught due to the coarse resolution. Giving a higher ResBW should pin-point if that is an issue.
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