Sven,
I know you’re alluding to digital being many, many analog frequencies and that’s your answer. When we test analog, we test individual frequiencies, and that in no way can be “digital”. Agree? When we keep adding more and more individual sinwaves we can start to ask when we can interpret voltage levels reliably in steps to becomes digital encoding. So that’s my answer.
When we start to GATE a signal as a mere high or low, we are now “deciding” a multiple superposition of analog waves is “digital”. We can also gate voltage levels such a PAM multi level encoding. The circuit breaks the analog into steps. Digital is the circuit that defines the logic steps, not the signal itself. That stays analog, yes.
So we kind of decide when our “analog” becomes digital and we can treat the signals as discrete voltage levels, and not a continuous stream of varying voltages. If we decide it is digital too soon, not enough frequencies, we get lots of errors. An eye pattern test can show the analog nature of digital.
The idea that digital (a means of capturing the data) is analog isn’t true. We switch how we interpret the voltage to encode discrete states. We don’t do that with an all analog system. So the signals may all be analog, but the treatment divides the system into analog, and digital.
The change to digital can be done on a discrete analog sigal, too. A max voltage can be encoded a “one” and the minimum voltage can be encoded a “0”. So we don’t even need to superimpose a bunch of signals to make a square wave and say that “shape” is digital. We just decided to switch HOW we capture the signal…a continuous stream, or gate it as a step voltage. Square waves are not digital, the encoding format is.
The way we capture the signal define analog or digital, not the signal itself. Both are feed analog, true, but we can switch spots in the circuit topology and go digital encoding any time we want.
So my statement is TRUE as I never switched to a “digital” encoding circuit did I!
Another way to look at this, once we use an AD, analog to digital, circuit we now interpret analog as digital. This is why it is called analog “to” digital.You’re right, the incoming signal was analog.