I/Q Modulation Considerations
Application Notes
I/Q Modulator Operation
First, consider an ideal I/Q modulator. As shown in Figure 1 above, a CW signal (at the carrier frequency) is fed into a quadrature power splitter, producing two signals which differ in phase by 90 degrees. This phase relationship is called “quadrature.” These signals are fed to the LO ports of two identical mixers. The IF ports (or low-frequency/DC ports) of these mixers are fed by the I and Q inputs respectively. These I/Q signals are referred to as “baseband” signals. The RF outputs of the two mixers are summed together, with, ideally, no phase shift between them. The resulting output from this structure is an I/Q modulated signal at the same carrier frequency as the LO.