Page 25 - EngineerIT July 2022

ADVANCED FILTER TECHNOLOGY

A size comparison of a typical 2 GHz to 18 GHz preselector block ADMV8913 is ideally suited for this application thanks to its low
is shown in Figure 13. In this comparison, the switched fixed filter insertion loss, small form factor and flexible digital interface
pre-selector bank is implemented with distributed filter technology options (either SPI or parallel control). These features allow it to
on a ceramic substrate. The size is estimated based on commercially be placed close to the front of these systems to ensure optimum
available filter technology. Eight-throw switches are included in performance, while reducing integration complexity.
the estimate to compare equivalent functionality. The tunable BPF
shown is the ADMV8818 that covers the same frequency range Conclusion
and offers full tuning flexibility over the switched filter bank. The The design considerations for an RF front end for a wideband
area savings of the ADMV8818 vs. a switched filter bank is greater receiver are numerous. The front end must be designed to handle
than 75%. The pre-selector functionality in a receiver signal chain difficult blocker scenarios, which are unpredictable, while also
typically takes up a sizeable portion of the overall size of the system, detecting low level signals. Being able to dynamically adjust the
so these area savings are critical in size limited EW systems that have front-end filtering performance to handle these blocker signals
the flexibility to trade off size with performance. is a critical feature for RF front ends. The new digitally controlled
The ADMV8913 is a combination of high-pass and low-pass tunable filter IC product offerings from ADI provide industry-
filters in a 6 mm × 3 mm package, and it is specifically designed leading performance with enhanced digital functionalities
for operation in the 8 GHz to 12 GHz frequency range (X band) addressing many front-end applications. These two new products
with low insertion loss of 5 dB. The high-pass and low-pass are just the first of many exciting new developments in the
filters are tunable with 16 states (4 bits of control) to adjust the digitally tunable filter portfolio. n
3 dB frequency (f 3 dB). Additionally, the ADMV8913 incorporates
a parallel logic interface that allows for setting the filter states For customers interested in learning more about these product
without the need for SPI communication. This parallel logic offerings, please visit the Digital Tunable Filters product page to
interface can be quite useful for systems that require fast filter see the latest data sheets or reach out to Andrew Athanasiou at
response times because it eliminates time needed for the SPI aathanasiou@arrow.altech.co.za
transaction. A functional block diagram of the ADMV8913 is
shown in Figure 14. References
Modern X band radar systems, whether they employ 1. Bezhad Razavi. RF Microelectronics. Pearson Education, Inc., 2012.
mechanically steered antennas or high channel count phase 2. David Pozar. Microwave Engineering, 3rd Edition. John Wiley & Sons, 2005.
3. Annino, Benjamin. “SFDR Considerations in Multi-Octave Wideband Digital
array beams, often rely upon filtering solutions that are compact Receivers.” Analog Dialogue, Vol. 55, No. 1, January 2021.
in size, have low insertion loss, and are easily configurable. The 4. Bowick, Chris. RF Circuit Design, 2nd Edition. Elsevier, Inc., 2008.
5. Delos, Peter. “A Review of Wideband RF Receiver Architecture Options.” Analog
Devices, Inc., February 2017.
6. Egan, William F. Practical RF System Design. John Wiley & Sons, 2003.
7. Tsui, James. Microwave Receivers and Related Components. Peninsula, 1985.
8. Tsui, James and Chi-Hao Cheng. Digital Techniques for Wideband Receivers.
SciTech, 2015.

About the Authors
Brad Hall is system applications engineering manager at Analog
Devices working in the aerospace and defense business unit in
Greensboro, North Carolina. He joined ADI in 2015. His focus is
primarily on full signal chain design support and new product
definition for aerospace and defense applications. Previously, he was
an RF engineer for Digital Receiver Technology, Inc. in Maryland. He
Figure 13: Fixed switched 2 GHz to 18 GHz BPF (left) vs. digitally tunable received his B.S.E.E. from University of Maryland in 2006 and his
2 GHz to 18 GHz BPF (right). The area savings are greater than 75%. M.S.E.E. from Johns Hopkins University in 2018.
David Mailloux is a product applications engineer within the RF
and microwave business unit at Analog Devices. He received both a
Bachelor and Master of Science degree in electrical engineering from
the University of Massachusetts Lowell in 2010 and 2012, respectively.
From 2010 to 2015, his experience includes working for Hittite
Microwave and Symmetricom (now Microchip Technology). He has
experience designing oscillators both at the semi-conductor and the
module level, and his theoretical background is complimented by
adept laboratory practices.
In 2015, he joined ADI as a product applications engineer
supporting highly integrated up/downconverters and tunable filter
products. Additionally, his technical support areas have included
voltage-controlled oscillators, phase-locked loops, frequency dividers
Figure 14: ADMV8913 functional block diagram. and frequency multipliers.

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