I searched for the CD4093 datasheet to see how it works and i read that is consists of 4 NAND gates with 2 inputs with Schmitt trigger function to each input. I read also that a Schmitt trigger is actually a comparator.So...
1)The high/low comparator is for the Schmitt trigger function or not?
The two comparators are used to sense if the input signal from the amp goes above or below 0V, the centre point of the expected signal.
When the amp signal goes pos/neg the comp output goes low.
As I want a high going pulse for the Res/Cap R17/C1 I use the 4093, as either input goes low the output goes high.
This high going edge, after differentiation by the R/C, drives the output low.
In order to get a high level to control the ON [Enb] pin of the 4066 I use a spare 4093 as an invertor.
If not, why do you use the comparators?
2)How can you make the NAND gate to operate as an OR Gate
Consider both inputs are high from the comps outputs, this means the 4093 output is low. If either of the inputs go low, then the output goes high.
So its effectively an OR gate when used in this way.
or as an invertor as you write at later stage of the circuit?
Connecting the two inputs together makes it an invertor.
3)What do you mean about high edge diff?
Consider the output of the OR gate is low, [both inps high] as either input goes low the output will go high 'while' either input is low.
We require a short pulse to be generated as the output goes high, this short pulse will be used to control the 4066 so that it only samples for the duration of the shortened pulse.
I appreciate your help!