Audio Signal and CMOS Ground

[jean-louise]

Hello!
I am a bit confused about the relation of the respective ground and negative rail in CMOS and audio circuits.
AFAIK a typical audio signal swings from V+ to V- around 0V. This is achieved with circuits using a bipolar power supply, where 0V in the middle is ground.
The Lunetta/CMOS-circuits all have a unipolar supply, also with 0V as ground but also as the negative extreme.
From what I gathered in the Lunetta world there is no real distinction between a digital (data) signal - the 0s and 1s - and a square wave audio signal. Also it seems like because it's all squarewaves at maximum volume there is not much of a need for a reference in the middle.
But what happens when I interface a Lunetta to an audio circuit like, e.g., an amp? Would then the negative half of the squarewave sit at ground and only the positive swing would be left?



Any help to deconfuse me would be very appreciated.

[blue hell]

Yes ... it's all above ground typically for CMOS stuff, but when you couple the signals out through a capacitor it would level out around zero. Most amps or computer audio interfaces would have an input capacitor anyway, so that'd be arranged automagically


To make sure you could add your own output cap of course .. hmm .. you want to know a value now I guess ... I'd start with around 10 µF ... the polarity direction .. + on CMOS side seems best ... when not enough bass increase it, but can't imagine that to be necessary.

[jean-louise]

Thank you!
Yeah, in the meantime I had begun to suspect something like a coupling capacitor would be beneficial.
But this reminds me again of how little I understand of the whole thing.
So for example if I have an squarewave osc going between 5V and 0V after coupling the circuits the 5V is interpreted as 2,5V and the 0V is interpreted as -2.5V?
How fast must the oscillation be to be interpreted as AC, does that depend on the capacity of the coupling capacitor?
In other words:
Is there a good read up about capacitors and capacitor coupling online anywhere, but, like, for dummies?

[blue hell]

Good questions

its bed time now tho .. but questions like yours eventually led to filter theory and all ... ok, for now ,,, the basics are .. it is an RC filter, the R being input or output impedance of your circuit, the C being the capacitor you throw in .. it really is just a handful of 'laws' and a bit of math ... Ohm, Faraday, Norton, Thevenin, Kirchhof .. that's about it ...

but yes .. a 50% duty cycle square would do as you described, a slow square would on average do the same, but it would distort the wave form too .. for your perception that would just kill some bass tho ... ah there is another 'law' I forgot ... Fourier .. about how arbitrary waves can be composed from sines .. harmonic sines even.

Anyway, that'd give some hints to google a bit and I'm off to bed for real now - if questions I'd try to explain it a bit of course, later

[jean-louise]

Thanks again! OK, I'm off to google

and good night

[varice]