VCO Output RF Switch

In order to form the NMR excitation pulse, the output of the VCO must be switched on and off very rapidly.  

The SA630 is a single-pole double-throw RF switch designed for use at 50R impedance, available as a surface mount SO8 package. The device requires only a +5V supply, and is controlled by a CMOS/TTL compatible enable pin. Although any supply voltage of between 3V and 5V is suitable, the noise figure is lowest at 5V and so it is desirable to use 5V. 

The switch has two poles corresponding to outputs 1 and 2, and these are internally terminated via 50R resistor and shorted to the ground via the AC_GND pin. All four RF IO’s, Input, Out 1, Out 2 and AC Ground are put in series with 10nF coupling capacitors and the supply voltage is decoupled with a 47uF tantalum capacitor and a 100nF ceramic capacitor.