My design of a DDS finally works OK but I want AC at the output. Block diagram attached.

My questions:

What is the correct place to get rid of the DC level?

A cap alone, is it the right way? If so, thinking of an output of 5Hz to 16 KHz what would be the right value?

Right now I have available non-polarized caps of 2uF and little space to parallel some.

What if I resort to an electrolytic or tantalum? How to know where the "+" terminal goes to?

Gracias for any help.

 

Remember that in any circuit there will be some R. So you have to take this into account and calculate the roll-off frequency:

\( f = \frac{1}{2\pi RC}\)

It is best to use non-polarized capacitors. If all you have are low value aluminum electrolytics, these are ok to use. At low voltages I would not worry too much about polarity but you can use a DC voltmeter across the cap in circuit and figure out which end is more positive.

 

Thanks for replying.

The pot already at point (C) is 10K. I think I could use it with a cap in series between the buffer and the amplitude control stage. Am I right?

What is the roll off frequency I have to look for? I am at lost here.

 

If you had a total series resistance of 10K in series with 2uF that would give you a roll off at about 8Hz.

 

After revising my options I came to the attached circuit.

1uF and 100K seem to work OK.

In way of recalculating the filter (with higher fc) to have the last KHz unattenuated.

Gracias for replying.