Digital Step Attenuators – Applications and Characteristics

In any radio or microwave equipment or solution there is a need to control the power level of the transmitted or received RF signal. Controlling the signal strength is a must to:

• Secure compliance with standards and regulations – and to avoid unhealthy radiation
• Avoid hardware damages due to excessive RF power levels
• Optimize performance of networks, receivers, transmitters and other RF functions

Consequently, there is a wide range of use-cases and applications for digital step attenuator solutions. Examples of varying complexity includes:

• Within any device used for wireless communication, from IoT modules to handsets wireless routers and mobile base stations, there is a need to adequately control the RF signal levels at various points in the design
• For larger systems and solutions, such as radio access networks, the overall efficiency is dependent of adequate balancing and control of the RF power levels in all parts of the network
• Throughout the product life-cycle of any radio or microwave equipment – from research and development, through homologation, production and maintenance, there is a need for extensive RF testing. This testing typically includes set-ups where the RF power levels, at various points in the set-up, can be controlled by means of digital attenuators.

What is a Digital Attenuator?

Generally speaking, an RF digital step attenuator is a device that is used to apply a controlled amount of attenuation to an RF signal – and where this amount of attenuation is digitally controlled. It is useful to distinguish between three different implementation levels of digital attenuators:

1. Integrated circuits (or even IP-blocks), for tight integration into high volume products. Requires detailed hardware and software integration
2. Digital attenuator modules, requiring less engineering effort, and for integration at system level
3. Stand-alone digital step attenuator solutions, typically including multiple, independent channels and covering a wide range of applications

Characteristics of Digital Step Attenuators

Irrespective of targeted application or implementation selected, any digital attenuator is characterized by of set of parameters such as operating frequency range, minimum and maximum attenuation, attenuation step-size and accuracy. Different applications require different parameters as well as selection of control interface. Typically, stand-alone digital step attenuator solutions intended for more general use exhibit the widest frequency and attenuation range as well as the highest accuracy.

Selecting an optimal step attenuator

To select a digital attenuator always start by understanding the application and the preferred implementation (integrated, module or stand-alone). As an example, a step attenuator intended for efficient, automated production testing of mobile devices would require a multi-channel stand-alone digital step attenuator solution with a wide frequency range, a high dynamic range and a high attenuation accuracy. For this purpose, Ranatec has a family of high accuracy, digital attenuator boxes, covering 100 MHz to 8 GHz and up to 110 dB attenuation. The state-of-the-art accuracy is obtained through a high precision attenuator design, along with an extensive factory calibration procedure. Thus, the actual attenuation can be known within +/-0.25 dB. These digital attenuator boxes can be optimized and configured to customer specifications, depending on the actual application.