A sample-and-hold circuit for microwave signals, using photoconductive switches

摘要

A sample-and-hold circuit for microwave signals comprises a bridge of matched metal-semiconductor-metal (MSM) switches 2,4,6,8. The switches 2 and 8 are activated by short light pulses from a pulse fibre laser 52 to transfer the input RF signal to floating hold capacitor 18. The bridge arrangement reduces the effect of leakage currents and capacitive feedthrough signals. MSM switch 12 is turned on by a laser pulse soon after the sampling switches 2 and 8 are opened, to reduce secondary carrier conductance effects in the switches 2 and 8. MSM switch 20 is then turned on by a laser pulse to clear the hold capacitor in preparation for the next sampling operation. The hold capacitor may be implemented by using the intrinsic capacitance of the switch 20. A low-temperature grown GaAs substrate may be used. The output differential amplifier 50 may be replaced by a passive power combiner having a subtractive effect (51, figure 3B).