A fast switching, high isolation absorptive SPST SiGe switch for 24 GHz automotive applications

Measured results for a high isolation, extremely fast switching SPST SiGe switch are presented. The switch provides /spl sim/35 dB of isolation between input and output over 15 GHz-26 GHz, yet is only 500 /spl mu/m/spl times/250 /spl mu/m in size. A novel load circuit ensures that there is almost no perceptible change in the input reflection coefficient of the switch between the transmission and the absorptive state. In the transmit state the switch provides gain for the input signal between 14.2 GHz and 25.5 GHz, and has a 1dB loss bandwidth of over 12 GHz. Lastly, the use of a constant current biasing scheme allows extremely fast switching between states allowing the switch to be used to generate RF pulses of 200 pS in length at a carrier frequency of 24 GHz, with rise and fall times of approximately 60 pS. The entire switch, including biasing circuitry, requires only 12 mA from a +5 V supply.