Modulators and Demodulators in wireless system development
I/Q Modulators and I/Q Demodulators
I/Q modulators and I/Q demodulators change the amplitude, frequency, or phase of a carrier signal in order to transmit information. I/Q modulators split an incoming data stream into its in-phase (I) and quadrature (Q) components, mix the resulting signals with local oscillators that are 90º apart in phase, and then combine the outputs vectorially in a 0º mixer. There are three basic types of modulation: amplitude modulation (AM), frequency modulation (FM), and phase modulation (PM). For each type of modulation, I/Q demodulators apply an RF signal to a 0º splitter. The resulting signals are then mixed with two local oscillators (LO) that are 90º apart in phase. Both output signals are in phase and quadrature.
I/Q modulators and I/Q demodulators can modulate signals, demodulate signals, or perform both modulation and demodulation. Modulator specifications include carrier frequency range and modulation frequency. Demodulator specifications include carrier frequency range, RF frequency range, output frequency range, and voltage standing wave ratio (VSWR). A unitless ratio ranging from 1 to infinity, VSWR expresses the amount of reflected energy at the input of the device. A value of one indicates that all of the energy passes. Any other value indicates that a portion of the energy is reflected. For I/Q modulators and I/Q demodulators, VSWR can also be expressed in terms of return loss (dB).