Hello,
I am using the TRF370333 I\Q Modulator in a low-IF radio architecture as the final up-mixer before the RF. The BPSK modulated complex single-ended I\Q signal which comes from the DAC5687 is converted to differential and is applied to the modulator's inputs.
The problem that I am facing is related to the image. It is not rejected. My IF is 4 MHz and the LO is 405.5 MHz. I get 401.5 and 409.5 MHz RF outputs both with the same power.
I think i know the problem but i was wondering how I can solve it. Since I am doing BPSK modulation, there is an AC signal located on a 3.3V DC in the In-Phase channel changing between 0 and 180 degrees. In BPSK, the Q channel is 0. So what I am doing is to leave the diffential Q inputs of the modulator stable at 3.3V without any AC signal applied on them.
I guess this is what results to the non-rejection of the image, but I cant see any way to solve it. Any suggestions? What type of signal should I apply to the Q inputs to reject the image and still maintain the properties of the BPSK modulation scheme.
Moysis
