Voltage double using ADS

Anyone can share the knowledge how to design and simulate a voltage multiplier using ADS at low voltage level ~1V?

The Villard circuit is a possibility. If you use low threshold diodes, you can attach a diode and capacitor. Similar to a half-wave supply.

A Villard style tripler will produce 2 V DC. As shown by a screenshot of my animated simulation.

how to choose the correct value of capacitor

Small capacitors will exhibit greater voltage swings and greater ripple.

The larger the capacitors, the less the voltage swing, and the less will be the ripple.

Their values can be about the same as you would choose to reduce ripple from a conventional power supply, according to how much your load draws, and the supply frequency.

Here is my recent Youtube video, showing animations of the above voltage tripler, plus two other types. It graphically portrays changing volt levels on the capacitors.

http://www.youtube.com/watch?v=KXppi0_b3NY