A monolithic microwave SPDT FET switch with resistances to counteract the effect of signals coupled to the control circuit

摘要

A monolithic SPDT switch comprises four FETs 1a-1d in a conventional series-shunt configuration controlled by command signals applied at pads 2a and 2b. The pads 2a and 2b are connected to the FETs by relatively long tracks (figure 1A) which may be subject to the coupling of high-frequency signals from the switched signal ports. To reduce the leakage of coupled high-frequency signals off-chip from the pads 2a,2b, resistors 12a-12d are placed in series with the tracks near to the pads. Similarly, series resistors 11a-11d placed near to the FET gates reduce the effect of coupled signals on the FET gates, thereby reducing ripple in the insertion loss characteristic (figure 2). The resistors 12a-12d may be placed within 200 microns of the control pads. The resistance of the resistors 11 and 12 may be set by adjusting the width of the tracks or by using different materials for the wiring patterns. Alternatively, lumped resistance elements may be used.