driving analog frequency through a digital component

[amitaiwe]

Hi to all,
I have a technical question which is actually a theoretical one:
What's the result of driving an analog frequency through a digital component, For example - trying to feed a sinousadle wave through a shift register and receiving a digital frequency at the output?
I guess the answer depends on the characteristics ​​of the analog signal and the digital component - accuracy, amplitude rate and the amount of time that the analog wave exists at a logic state (There's a term for that I think...).
Thinking about it theoretically my answer would be, at least for the specific case, why not? If the amplitude rate of the
analog wave is included in the '1' logic rate of the shift register so the frequency of the digital output will be the same as the
analog input.
Thanks,
Amitai

 

[crutschow]

Generally digital circuits require the input signal have a minimum rise and fall time for proper operation, thus the AC signal is typically converted to a digital signal with the proper characteristics by a comparator circuit IC. What is the highest AC frequency you have?

 

[FvM]

There are different ways to represent analog quantities by digital signals, you didn't clarify well how you want it to do.

"analog wave is included in the '1' logic rate of the shift register" can you sketch a simple example with analog and respective digital waveform? The description might be understood either as pulse-frequency or sigma delta modulation.

 

[amitaiwe]

Generally digital circuits require the input signal have a minimum rise and fall time for proper operation, thus the AC signal is typically converted to a digital signal with the proper characteristics by a comparator circuit IC. What is the highest AC frequency you have?

What I'm thinking of doing is driving a frequency signal of 500hz (not Khz) through a CMOS CD4034B SR and
having an digital output of the same frequency. I'm aware that it might be better to use a MUX instead,
but still I want to try and see the result.

There are different ways to represent analog quantities by digital signals, you didn't clarify well how you want it to do.

"analog wave is included in the '1' logic rate of the shift register" can you sketch a simple example with analog and respective digital waveform? The description might be understood either as pulse-frequency or sigma delta modulation.

What I mean is an digital output which has the same frequency as the analog input, no matter what the output's shape.
Looking from the point of view of the SR - doesn't he "see" a logical '1' at his input when the analog frequency's amplitude is
in the '1' logical rate of the shift register and '0' otherwise?

The ideal case of what I mean is as shown here:


Amitai

 

[FvM]

In this case, a comparator as suggested by crutschow is the exact solution.