A Fast Switching, High Isolation Absorptive SPST SiGe Switch for 24GHz Automotive Applications

Measured results for a high isolation, extremely fast switching SPST SiGe switch are presented. The switch provides ~35dB of isolation between input and output over 15GHz-26GHz, yet is only 500μm × 250μm 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 14.2GHz and 25.5GHz, and has a 1dB loss bandwidth of over 12GHz. 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 200pS in length at a carrier frequency of 24GHz, with rise and fall times of approximately 60pS. The entire switch, including biasing circuitry, requires only 12mA from a +5V supply.