Evaluation Engineering - 25

Looking forward
In summary, this novel design example for a PXI Dual SP8T
Multiplexer demonstrates how the use of MEMS switches can
eliminate many of the compromises that are necessary when
working with either EMR or solid-state switching technologies.
Given the small size, there are many improvements that will be
possible in the near future.
Current research and development is focused on (1) delivering
considerably lower loss with optimized designs, such as " switchmatrix-in-a-package " , (2) the ability to provide both reflective and
terminated versions, and (3) extensions to mmWave frequencies,

Figure 2. SP8T RF Board Switching Diagram

and ultra-low off capacitance (Coff). A low switch
on-resistance (Ron) enables
achieving a total insertion
loss of <3 dB at 8 GHz from
one input to one output
with high power handling
capability of 8 Watts CW
input power.
Figure 3. SP8T RF Board Design
The ultra-low Coff directly contributes to this design's target off-state isolation of
80 dB. Switching on-off operation is less than 20us and this is
typically a 750 times improvement over competing relay-based
switches. One strong point of traditional EM solutions is that
they often have total lower insertion losses through the switches
and matrix, but the tradeoff is that they have much shorter
operating lifetimes. This is also apparent when operating an
EM-based system at higher power levels, often referred to as
" hot switching " and EM relays exhibit even shorter operating
lifetimes under higher RF power levels.
The other comparison is to solid-state switch-based multiplexers or matrices. While switching lifetimes are usually much
longer than EM or MEMS-based switches, their insertion losses
are usually noticeably higher and limited in RF input power levels
due to device compression curves and lower linearity. Table 1
shows the specification of the MEMS-based PXI Dual SP8T multiplexer module compared with typical EM or solid-state designs.
Key performance benefits are in the areas of insertion loss, size,
weight and power consumption, as shown in Figures 4 and 5.
Table 1. MM5130 based PXIe Dual SP8T Value
EM Relay

Solid State

MM5130

SP6T

SP8T

Dual SP8T

Channel Density
(# of ch/slots)

6/4 = 1.5

8/1 = 8

16/1 = 16

Switching Speed

<15ms

122us

<20us

Insertion Loss

0.2dB @ 3GHz
0.4dB @ 6GHz

3.6dB @ 3GHz
5.3dB @ 6GHz

1.2dB @ 3GHz
2.6dB @ 6GHz

Good Insertion Loss. Can be improved
with an optimized MEMS switch.

Off-State
Isolation

70dB @ 3GHz
60dB @ 6GHz

94dB @ 3GHz
77dB @ 6GHz

95dB @ 3GHz
80dB @ 6GHz

Better Isolation. Can be increased up tp
100dB+ with an optimized MEMS switch.

>57dBm

>85dBm

>100W

Configuration

Switching
Operations

IP3
Power Handling

Benefits

Up to 10 increase in channel density
> 750 X switching speed improvement
enables faster measurement
> 500 X reliability improvement
reduces system downtime

Can be increased up tp 100W+ with an
optimized MEMS switch.

Figure 4. Typical Insertion loss up to 10 GHz.

Figure 5. Typical Off-State Isolation up to 10 GHz.

up to 50 GHz. In addition, while the channel count is currently
limited by the connector interface on the PXIe platform, the
miniature size of the MEMS switch allows for the creation of
much higher density switch matrices, to hundreds of channels,
in custom assemblies.
With the seemingly endless proliferation of new frequency
bands, for both commercial 5G and military systems, the complexity of the test systems will continue to increase. The ability
to have an RF switch multiplexer that not only meets the RF performance requirements, but also saves crucial space in the PXI
chassis, will provide a big efficiency savings for test engineers. In
addition, the MEMS-based approach provides significant cost of
ownership reductions over EM solutions given the significantly
higher reliability and switching speed.
NOVEMBER/DECEMBER 2020 EVALUATIONENGINEERING.COM

http://www.EVALUATIONENGINEERING.COM

Evaluation Engineering

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