Voltage Doubler.

This is the simple circuit which is evolved from two basic circuits.

Voltage doubler =Positive clamper +Peak detector. 

Suppose you have a sine wave of peak voltage 5v. i.e Peak to peak voltage of 10v. How to get output which is double the input voltage.

Output=2*Peak voltage.

Here is the circuit

The two circuits are already discussed 

POsitive clamper

Peak detector

In this circuit we just make use of these concepts to get voltage which is twice the input peak voltage.Hence the name voltage doubler

If you check after 5ms output will be double.Here you can see output is not 10v but approximately 9.8v. This is because diodes used are not ideal. Add 0.19 voltage to the positive clamper as shown below  to get exact 10v.(Those who are fond of exact results ;) ) 

The simulator used is Pspice.