Design of a New Radio-Frequency Switch Topology with Very Low Polarization Current

What is it about?

Embedded systems are generally powered by batteries, characterized by a limited duration of electrical energy storage. For that, low power consuming RF components are often used. This work focuses on the design of a new RF switch based on one varicap diode within a series/parallel circuit topology. The latter is low-power-consuming in both ON and OFF mode and inhibits eventual nonlinearities caused by series diodes such as common PIN diodes. Before performing simulations, the diode has been characterized experimentally in the whole UHF band of interest and the extracted S-parameters have been used in the simulations of the resonating structure. The optimized switch has been measured and has showed a good agreement with simulated results in terms of high isolation (50 dB) and low insertion loss (0.1 dB). These results showed better performances compared to other structures based on RF MEMS, PIN diode or FET transistor devices, available in the literature.

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Why is it important?

In this article, we presented a new RF switch topology, made in microstrip technology. It has multiple advantages such as low manufacturing cost, simplicity of design, ease of reproducibility, low insertion loss, low power consumption and good linearity over PIN diodes and FET transistors. It is bi-directional and its control is based on a resonant circuit, placed in parallel with the load. The switching of the latter, of a series resonance (open switch) to a parallel resonance (closed switch) is provided by a varicap diode. The latter is a frequently available and inexpensive component. It is controlled by a DC voltage and operates with an almost negligible reverse bias current (10 nA), which is much lower than that required by a PIN diode (10 mA). This switch has been tested and characterized in the UHF band. Its switching time is of the order of microseconds. In the off-state, it has good insulation, of the order of 50 dB. In the on-state, the resonant circuit has an infinite impedance and the RF switch is transformed into a transmission line with a characteristic impedance ZC = 50 Ω. This makes it possible to manage a considerable power, without distortion of the RF signal and with a low insertion loss. The size of the realized RF switch can be considerably reduced by replacing the distributed elements (inductances and capacitors) with localized elements.