Do you have any suggests to provide a negative votage when using SPDT switch like HMC232? The control voltage is negative but we need to connet to positive control voltage like a CPLD outputs. Thanks!

  • There are circuits DC-DC converters available to provide an inverting function (take a positive input and give a negative output), but for small currents it may be more cost effective to do the following:
    Build an oscillator that will provide a current output capableof about 50% to 100% higher than the current you need and an output voltage that is about 30% greatere than the negative voltage you need, but with an output that is always positive. A 555 timer would do nicely. If the oscillator will not provide the current you need, follow it with a buffer amplifier that will provide sufficient current. From this connect the circuit shown here to provide your negative voltage. I suggest capacitor values that will have an impedance of less than 50 Ohms at the oscillator frequency. I suggest an oscillator frequency above 1 kHz. For the diodes, early any diode will work except Zener diodes. Something like the 1N4001 or even the 1N4148 will suffice.