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ADVANCED FILTER TECHNOLOGY

input section has four high-pass filters and an optional bypass that
is selectable by the two RF switches. Similarly, the output section
IN
has four low-pass filters and an optional bypass that is selectable
by the two RF OUT switches. Each of the high-pass and low-pass
filters are tunable with 16 states (4 bits of control) to adjust the 3
dB frequency (f 3 dB). Figure 10 shows a functional block diagram of
the ADMV8818.
Thanks to its rapidly reconfigurable flexible architecture and
small form factor, the ADMV8818 provides full coverage over the 2
GHz to 18 GHz band without any dead zones. The ADMV8818 can be
configured as a sub-octave preselector filter, image, or IF filter. When
configured in a signal chain as shown in Figure 11, the receiver can
maintain high sensitivity with the ability to switch to the ADMV8818
as a pre-selector in the presence of a larger OOB signal.
For example, if a signal of interest is being received near 9
GHz but a strong OOB blocker is present at 4.5 GHz, then that
Figure 10: ADMV8818 functional block diagram.
blocker signal can cause harmonics to show up near the desired
9 GHz signal, preventing operation. Configuring the ADMV8818
Latest filter solutions as a 6 GHz to 9 GHz band-pass filter would allow for a wideband
Analog Devices has developed a new family of digitally tunable signal to pass through while properly knocking down the level
filter products that use an enhanced semi-conductor process of the blocker before it can cause harmonic issues to crop up
along with industry friendly packaging techniques. This technology in the non-linear elements of the signal chain. An S-parameter
results in small, high rejection filters that alleviate the blocker sweep of the ADMV8818 configured for this case is overlaid with
issues that arise in a receiver. These filters are designed to be blockers and shown in Figure 12.
highly configurable by standard serial to parallel interface (SPI)
communication, with fast RF switching speeds. Additionally, ADI
has incorporated a 128-state look-up table within each chip to
allow for quickly changing filter states for fast frequency hopping
applications. The combination of fast tuning with high rejection
and wide frequency coverage enables the next generation of
receiver applications operating in adverse spectral environments.
The latest products to be introduced using this technology are
the ADMV8818, which has four high-pass and four low-pass filters
operating from 2 GHz to 18 GHz, and the ADMV8913, which has
a high-pass filter and low-pass filter operating in the 8 GHz to 12
GHz frequency range.
The ADMV8818 is a highly flexible filter in a 9 mm × 9 mm
package that can achieve tunable band-pass, high-pass, low-pass,
or bypass response between 2 GHz and 18 GHz. The chip consists Figure 12: ADMV8818 configured as a 6 GHz to 9 GHz band-pass filter.
of two sections: the input section and the output section. The The filter rejects F2 – F1, F1 + F2, F/2, and F × 2 spur products.

Figure 11: A block diagram of a 2 GHz to 18 GHz receiver using ADMV8818 as a pre-selector and image filter.

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