Circuit Note CN-0377 Devices Connected/Referenced Circuits from the Lab reference designs are engineered and tested for quick and easy system integration to help solve todays DC to 14 GHz, Single-Pole, Four-Throw analog, mixed-signal, and RF design challenges. For more ADGM1304 MEMS Switch with Integrated Driver information and/or support, visit www.analog.com/CN0377. DC to 2.5 GHz Switchable RF Attenuator Implemented with RF MEMS Switches The switches must be as transparent as possible to the RF signal EVALUATION AND DESIGN SUPPORT and add as little insertion loss and distortion as possible. The Circuit Evaluation Boards ADGM1304 switches offer best in class insertion loss of 0.26 dB CN-0377 Circuit Evaluation Board (EVAL-CN0377-EB1Z) typical at 2.5 GHz, and a third-order intercept (IP3) performance Design and Integration Files of 69 dBm typical. In addition to insertion loss and distortion, Schematics, Layout Files, Bill of Materials another key benefit that the MEMS switch brings to this CIRCUIT FUNCTION AND BENEFITS application is its ability to operate down to true dc. This means the switches do not limit lower frequency operation in a typical The circuit shown in Figure 1 uses RF MEMS switches to route RF instrumentation attenuator switching application, and enables an RF signal between two surface-mount RF attenuators and the instrument to pass dc bias voltages when required. two straight through paths. The physical size of the ADGM1304 device at 4 mm 5 mm Attenuating RF signals is commonly done in RF test instrument- 0.95 mm yields a significant reduction in printed circuit board tation and receiver front ends to protect downstream circuitry (PCB) area compared to traditional electromechanical relays and to increase dynamic range. Using discrete attenuators and switching solutions. In addition, the actuation speed of the switches maximizes design flexibility and routing options. In ADGM1304 switch is 30 s, a significant improvement over the Figure 1 circuit, two ADGM1304 single-pole, four-throw electromechanical relays, which are in the order of milliseconds (SP4T) RF MEMS switches in a back to back configuration yield and introduce significant time lag in measurement systems. four independently switchable paths between input and output. The actuation lifetime of the ADGM1304 device is guaranteed Two of the paths are straight through transmission lines, the for one billion cycles, which is a major improvement over third path contains a 6 dB attenuator, and the forth path contains electromechanical relays and significantly increases overall a 9 dB attenuator. Key to realizing this application is the use of system reliability. ultralow insertion loss and highly linear switches to multiplex between the different path options. 9dB ATTENUATOR ADGM1304 ADGM1304 6dB ATTENUATOR Figure 1. RF Switchable Attenuator Simplified Circuit Diagram Rev. A Circuits from the Lab reference designs from Analog Devices have been designed and built by Analog Devices engineers. Standard engineering practices have been employed in the design and construction of each circuit, and their function and performance have been tested and verified in a lab environment at room temperature. However, you are solely responsible for testing the circuit and One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. determining its suitability and applicability for your use and application. Accordingly, in no event shall Tel: 781.329.4700 www.analog.com Analog Devices be liable for direct, indirect, special, incidental, consequential or punitive damages due Fax: 781.461.3113 2016 Analog Devices, Inc. All rights reserved. to any cause whatsoever connected to the use of any Circuits from the Lab circuits. (Continued on last page) 13580-001CN-0377 Circuit Note The RF edge launch SMA connectors are manufactured by CIRCUIT DESCRIPTION Rosenberger (32K243-40ML5) and have a frequency range of Figure 2 shows a close up photograph of the circuit evaluation dc to 18 GHz. The PCB material stack-up used is shown in board. The switches are marked in black. The ADGM1304 Figure 3 and is the same as for the EVAL-ADGM1304EBZ switches have a SP4T configuration therefore, in a back to back evaluation board. arrangement, four individually selectable paths can be achieved. The surface-mount attenuators can be seen as the white Metal 1 Finished Copper Plating: 1.5 oz (2.1 thou/53 m) Rogers RO4003C: 8 thou laminate, Er 3.38 components in Figure 2. They are manufactured by EMC starting copper weight 0.5 oz/0.5 oz Technology. The 6 dB and 9 dB attenuators (TS0606F and Metal 2 Copper Weight: 1 oz (1.4 thou/35 m) TS0609F, respectively) have an optimal performance frequency range of dc to 10 GHz and a peak power handling level of 2 W (33 dBm). The ADGM1304 MEMS switches have a 3 dB ~37.2 thou FR4 bandwidth of up to 14 GHz and a power handling level of 36 dBm (continuous wave) and are therefore ideally suited for use with these attenuators. Metal 3 Copper Weight: 1 oz (1.4 thou/35 m) Rogers RO4003C: 8 thou laminate, Er 3.38 6dB starting copper weight 0.5 oz/0.5 oz ATTENUATOR Metal 4 Finished Copper Plating: 1.5 oz (2.1 thou/53 m) CPWG RF trace width: 15 thou ADGM1304 CPWG RF trace to ground gap: 12.2 thou Final overall PCB thickness: 62 thou Final copper plating thickness on top and bottom layers: 1.5 oz Figure 3. PCB Stack-Up with Co-Planar Waveguide with Ground (CPWG) Dimensions ADGM1304 Figure 4 shows the full schematic for the PCB. The links marked CH1 to CH4 select between each of the four paths (two through paths and two attenuator paths). Because all these paths are 9dB independently controllable, they can all be on, all off, or any ATTENUATOR other combination thereof as necessary. Figure 2. EVAL-CN0377-EB1Z Circuit Board Rev. A Page 2 of 6 13580-002 13580-003