RF MEMS Switch
Implementation
Hermetically sealed
switch contacts
Actuation lifetime: 1
billion cycles (minimum)
Signal Generators (Audio
through RF)
Automated Test Equipment
Electronic Test &
Measurement
Aerospace and
Defense
Communications
Wideband RF Signal
Processing
The circuit shown in Figure 1 uses RF MEMS switches to route an RF signal between two surface-mount RF
attenuators and two straight through paths.
Figure 1. RF Switchable Attenuator Simplified Circuit Diagram
Attenuating RF signals is commonly done in RF test instrumentation and receiver front ends to protect downstream
circuitry and to increase dynamic range. Using discrete attenuators and switches maximizes design flexibility and routing
options. In the Figure 1 circuit, two ADGM1304 single-pole, four-throw (SP4T) RF MEMS switches in a back to back
configuration yield four independently switchable paths between input and output. Two of the paths are straight through
transmission lines, the third path contains a 6 dB attenuator, and the forth path contains a 9 dB attenuator. Key to
realizing this application is the use of ultralow insertion loss and highly linear switches to multiplex between the different
path options.
The switches must be as transparent as possible to the RF signal and add as little insertion loss and distortion as
possible. The ADGM1304 switches offer best in class insertion loss of 0.26 dB typical at 2.5 GHz, and a third-order
intercept (IP3) performance of 69 dBm typical. In addition to insertion loss and distortion, another key benefit that the
MEMS switch brings to this application is its ability to operate down to true dc. This means the switches do not limit lower
frequency operation in a typical RF instrumentation attenuator switching application, and enables the instrument to
pass dc bias voltages when required.
The physical size of the ADGM1304 device at 4 mm × 5 mm × 0.95 mm yields a significant reduction in printed circuit
board (PCB) area compared to traditional electromechanical relays switching solutions. In addition, the actuation speed
of the ADGM1304 switch is 30 μs, a significant improvement over electromechanical relays, which are in the order of
milliseconds and introduce significant time lag in measurement systems. The actuation lifetime of the ADGM1304 device
is guaranteed for one billion cycles, which is a major improvement over electromechanical relays and significantly
increases overall system reliability.
Figure 2 shows a close up photograph of the circuit evaluation board. The switches are marked in black. The
ADGM1304 switches have a SP4T configuration; therefore, in a back to back arrangement, four individually selectable
Circuit Function & Benefits
Circuit Description