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The “I” in IQ stands for “in-phase” and the “Q” stands for “quadrature.” IQ mixers allow the two frequency sidebands to be handled separately using quadrature modulation where phase becomes a variable in data transmission. Quadrature modulation ultimately doubles the information content in a double-sideband transmission since each sideband can contain different information. The block diagram of an IQ mixer is shown in Figure 10:

Figure 10: Block diagram of an IQ mixer.

An IQ mixer comprises two mixers, each with the LO phase shifted by 90° from the other with a hybrid coupler. One mixer handles the in-phase LO component, and the other handles the quadrature component. The I and Q output signals are baseband signals combined into an RF signal for transmission. At the receiver, the process is reversed with the RF signal separated back into 1 and Q baseband channels. Any of the unbalanced or balanced mixer topologies discussed here can be used to create the IQ mixer configuration.

Mini-Circuits uses the terminology modulators/demodulators to classify many of its IQ mixer products, which can be found under the “Modulators/Demodulators” section of the website.

Figure 11: Block diagram of an image reject / single sideband mixer.