RF MEMS Switches and Integrated Switching Circuits by Ai-Qun Liu

Author:Ai-Qun Liu
Language: eng
Format: epub
Publisher: Springer US, Boston, MA

5.2 Design of the SP3T Switching Circuit

Based on the design of the in-line SP2T switching circuit, a new type of SP3T switching circuit is developed as shown in Fig. 5.8a, b. Each branch is perpendicular to the adjacent branch. The bias voltage is applied between the signal line and the ground line at the output port. At any time only one switch is activated to the close state and other two switches are at the open state. Then, the RF signal propagates along the transmission line from the input port to only one of the output ports. Four bond wires are required to equalize the potential of the ground planes. The lumped equivalent model is obtained by adding a branch with an open switch to the lumped equivalent model of the SP2T switching circuit, as shown in Fig. 5.8c. The SP3T switching circuit consists of two open stubs connected between the input transmission line section and output branch section with a closed switch. Since the open stubs are capacitive in nature, when there are more open stubs, higher loss is expected at high frequencies range. Therefore, the insertion loss of the SP3T switching circuit is expected to be larger than the in-line SP2T switching circuit.

Fig. 5.8The SP3T switching circuit: (a) schematic diagram; (b) layout design (G, ground; S, signal; , bond wire); and (c) lumped equivalent circuit

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