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Integrating multiple functions into compact modules is becoming necessary to meet the needs of RF/microwave component customers. Highly integrated devices, such as variable gain amplifiers (VGAs), offer a wider range of uses than a standalone attenuator (Fig. 4). VGAs are used to condition signals with a programmable voltage gain. To accomplish this, some VGAs are designed with variable attenuators in the same signal chain as a fixed gain amplifier. This enables those VGAs to offer signal attenuation and amplification in the same device. In doing so, they can meet the testing and operational needs of a variety of applications. In communications setups, a VGA could be used to adjust the voltage input into a cable system to maintain signal integrity and amplitude despite the cable length or receiver configuration.

Price, Power, And Size Drive Attenuator Advancement, Fig. 4

Agilent and RFMD both offer VGAs that can operate in the gigahertz range and either amplify or attenuate signals. These devices are designed as components of cellular systems. Agilent offers a VGA with an output frequency range of 0.25 to 2.4 GHz, gain ranging from 5 to -30 dB, and a 1-dB step size. RFMD reports that its VGA has a frequency range of 0.05 to 4.00 GHz with gain of 18 to -13.5 dB and a step size of 0.5 dB.

An RF vector multiplier can operate as a variable attenuator, phase shifter, multiplexer, and vector modulator. It is composed of a matched pair of broadband VGAs with summed outputs. Separate gain controls enable independent and linear-in-magnitude control. Agilent and Maxim Integrated are examples of companies that offer vector multipliers operating in cellular bands.

Today, the trend for RF/microwave attenuators is to provide on-demand customization in a wide range of package sizes. For designers, this trend translates into demands for tighter phase variation, higher accuracy, low PIM, and higher resolution. Higher-frequency operation, higher power, faster switching, and broader-bandwidth demands lead to larger designs that can handle higher-temperature operation.

To keep up with the cellular industry, complex modules with combined functionality and very high bandwidths are needed to stay price competitive. Oftentimes, these design constraints conflict with present technology capabilities, which puts pressure on RF/microwave attenuator designers to stay up to date with the latest materials and technologies.

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