ADGM1004 Data Sheet
Rev. A | Page 18 of 20
SUGGESTED APPLICATION CIRCUITS
SWITCHABLE RF ATTENUATOR
RF attenuator networks are commonly used in RF instrumenta-
tion equipment such as vector network analyzers, spectrum
analyzers, and signal generators. Routing RF signals through an
attenuator can enable the equipment to accept higher power signals
and, therefore, increase the dynamic range of the instrument. In
RF attenuation applications like the vector network analyzers,
spectrum analyzers, and signal generators, maintaining the
bandwidth of the signal after it passes through the network is
critical. Any degradation of the signal reduces the performance of
the equipment. Therefore, the RF characteristics of the switches
used for routing are an integral part of the quality of an attenuator
network.
The ADGM1004 MEMS switch with low flat insertion loss,
wide RF bandwidth, and high reliability is suited for use as a
switchable RF attenuator. The ADGM1004, as an SP4T switch, also
brings added flexibility. Figure 37 shows an example attenuation
network configuration using two ADGM1004 switches and three
different attenuators. The fourth channel of the switches is used
as a nonattenuated route in Figure 37.
15dB
10dB
I/O
ADGM1004
5dB
I/O
ADGM1004
15173-127
Figure 37. Switching RF Attenuators Using ADGM1004 MEMS Switches
RECONFIGURABLE RF FILTER
A reconfigurable RF filter is advantageous in many RF front-
end applications. A reconfigurable RF filter provides more
saved space. As space becomes more constrained in applications,
the option to have an economical reconfigurable RF filter
instead of individual frequency dependent filters is attractive.
The ADGM1004, with its low flat insertion loss, wide RF
bandwidth, low parasitic, low capacitance, and high linearity, is
needed to turn on the lump components (capacitor, inductor),
which make the MEMS switch suited for reconfigurable filter
application.
In applications such as wireless communications or mobile
radios, the number of bands and/or modes constantly increases.
A reconfigurable RF filter allows more bands/modes to be
covered using the same components.
Figure 38 shows an example of a reconfigurable band-pass filter.
The topology shown is of a generalized two-section, inductively
coupled, single-ended band-pass filter, nominally centered on
400 MHz ultrahigh frequency (UHF) band. The MEMS
switches are positioned in series with each of the shunt
inductors.
The function of the switches includes or omits a shunt inductor
from the circuit. Changing the shunt inductor value affects the
bandwidth and center frequency of the filter. Using inductance
values from 15 nH to 30 nH significantly alters the bandwidth
and center frequency, allowing the filter to dynamically configure
to operate in the UHF or very high frequency (VHF) bands
while preserving the 50 Ω match on the input and output ports.
The low R
ON
value and wide bandwidth of the MEMS switch
makes it an ideal choice for this application. The low R
ON
reduces
the negative effect a series resistance has on the quality factor of
the shunt inductor. The large bandwidth enables higher frequency
band-pass filters.
Figure 38. Reconfigurable Band-Pass Filter Achieved Using Two ADGM1004 MEMS Switches
