How to select RC value for a full wave rectifier?

[shaikss]

Hi,

I have designed a rectifier using MOSFETS.
Now, my question is how to select the R, C values for filtering/smoothening purpose provided my input RF voltage is 1V at 865MHz?
Can you please guide me?
What are the various aspects to keep in mind while selecting R, C value?
Thanks a lot in advance.

 

[BradtheRad]

There is a formula you can use. I forget how it goes.

A roundabout method is to calculate an RC time constant that will yield a certain amount of ripple between crests.

For instance, if you want .01 V ripple, then volt level is permitted to fall that amount during .58 nSec between peaks.

The time constant is for a 63 percent change. This means your time constant will be 63 * .58 nSec (the curve isn't straight, but this should be good enough)...
equals 36 nSec.

Divide by your load, 1000 ohms (per your schematic). This yields a capacitor value of 36 pF.

You'll get better than .01V ripple since the waveform is not a void between peaks.