Modern Signal Generators Simplify I/Q Modulator Characterization

In-Phase/Quadrature (I/Q) Modulators are crucial to modern telecommunications. Currently, designers are working on I/Q modulators to meet the increasing demands for transmission bandwidth and signal quality. The performance of such devices must be evaluated during the design phase. In "Characterization of IQ Modulator Counts on Flexible Signal Generator Stimulus," Tektronix, Inc. (Beaverton, OR) delves into several of the key measurements that engineers routinely make on an I/Q modulator.

The goal of this 14-page application note is to show how modern arbitrary-waveform/function generators provide a stimulus to thoroughly characterize high-performance I/Q modulators. Compared to previous methods, these generators also promise to deliver flexibility and time savings. Quadrature amplitude modulation (QAM) is at the heart of this white paper, as most of today's telecommunication relies on QAM to map data onto an RF carrier. In QAM, every logical state is assigned to a specific amplitude and phase value.

The note introduces an efficient way to generate the modulating (baseband) signal with a specific amplitude and phase. It then explains how an engineer should choose the right signal generator. The bulk of the paper is spent on the measurements themselves. A one-page sidebar, "Creating Dual Tone Waveforms with ArbExpress," provides information on creating dual tones for intermodulation-distortion measurements on an I/Q modulator via waveform math. This application note serves as a good primer for any engineer who will be using a modern arbitrary/function generator to characterize I/Q modulators.

Tektronix, Inc., 14200 SW Karl Braun Dr., P.O. Box 500, Beaverton, OR 97077; (800) 835-9433, Internet:

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