Today I will be writing about the ADRF5740 attenuator, one of the newest solutions from Analog Devices designed for 10 MHz to 60 GHz communication systems. The ADRF5740 does what its name suggests, it attenuates – lowers - the strength of incoming and outgoing RF signals. I was, at first, confused with the idea of ever wanting to lower the power of a radio. You see, my first job after college was at a small AM radio station in New Jersey. (The station was VERY small - as was the pay - but oh, the glamour of being in showbiz…) Anyway, considering the station’s night-time 500-watt signal barely made it to the county line, the last thing on the owner’s mind was lowering power. Yet, as I learned, attenuation is critical to the operation of base stations, satellites, test equipment, radar and other applications.
These systems detect the strength of an incoming signal and determine if the transmitter can run at lower power. Not having to constantly run at full power not only saves operating cost but helps lengthen the life of transmitter components. On the receive side the same is true: digital attenuators scale down the incoming RF signal to match the safe operating limits of other components in the circuit. This, in turn, translates into fewer hours for maintenance and repair, thus improving the lifetime value of a system.
The ADRF5740 was designed “application agnostic,” meaning it brings these cost-saving benefits to all systems with frequencies from 10 MHz all the way up to 60 GHz. (Those numbers themselves are very impressive as the ADRF5740 has an extremely wide range of frequencies on which it can operate, making the part a great single source for a wide range of applications.)
Adding attenuation requires the part be inserted into a radio circuit. Paradoxically, attenuators built into circuits for the purpose of improving radio performance can actually add their own, unwanted signals to the circuit, almost defeating their purpose. While impossible to eliminate entirely, the ADRF5740 attenuator’s insertion loss is ultra-low, in fact the lowest in the industry for such a wide operating frequency range.
Digital attenuator – what’s so special about that?
Designers of the ADRF5740 wanted to include, on the same chip, an interface to digital devices such as microcontrollers and Field Programmable Gate Arrays (FPGAs) so the level of attenuation could be accurately set by the user. The ADRF5740 was built using Silicon on Insulator (SOI) process, which isolates the RF and digital circuitry from each other. Designers of the digital side of the ADRF5740 also took advantage of the isolation properties of SOI to build the digital interface as CMOS, which has long been the standard for digital circuitry. In this way the ADRF5740 not only makes it easier to design the transmit and receive signal chains but also to implement in almost any solution with digital control. The SOI process gives the designer the potential to optimize the ADRF5740 for faster response, speed being extremely important in applications such as instrumentation and radar applications. The faster the device, the faster the system performs.
Other benefits of the ADRF5740
Along with the digital interface, the ADRF5740 includes features that make the design of transmitters and receivers simpler and less expensive. For a radio to work to its maximum efficiency it is critical the output impedance of the transmitter be matched to the impedance of the antenna. (An analogy for impedance would be when a 1/2” garden hose is connected to a 1/4” hose. To ensure the most amount of water flows, the hoses need to be the same diameter.) Because the ADRF5740 presents a consistent 50 ohms (the universal standard for impedance in radios and test equipment) no extra impedance matching circuitry is required. Benefits include faster design time, lower power consumption and reduced board space.
To sum up, the ADRF5740 is part of a complete signal chain for just about any RF or microwave circuit from 10 MHz all the way up to 60 GHz. If you’re curious to read even more about the ADRF5740 digital attenuator, please visit the product page here.