[sdiy] 4069 VCO to get started? My answer

[Richard Wentk]

At 14:32 04/10/2004 +0200, Nicolai Czempin wrote:
>Laurie Biddulph wrote:
>
>>Hello Nicolai,
>>
>>Although the 4069 is fundamentally a logic IC it is actually used in this 
>>application as a linear device and utilises the fact that at lower power 
>>rails the gates can actually be treated as linear/analogue devices. This, 
>>therefore, does make the 4069 a suitable device for your initial requirements.
>>
>Okay, I'll accept it even if I can't quite follow...
>What kind of "analogue devices"?

It's basically just a buffer, which gives you a neat way of controlling the 
charging current of a capacitor.

The analogue/digital dichotomy is a bit simplistic because digital circuits 
are still analogue circuits being made to work in a specialised way. A lot 
of the time you can ignore the fact they're analogue and use a 
much-simplified digital model of how they work. But in some cases, like 
this one, it's worth understanding the underlying analogue properties.

If you ever have to interface digital to analogue - as you often do - 
you'll again need to understand the analogue properties of supposedly 
digital voltage and current behaviour.

It's true some books start with digital because there's less to learn and 
it's cleaner and simpler than analogue. But you can't do reliable circuit 
design, even digital design, without a good grounding in analogue basics.

And then once you have that you can go on to learn about RF, which is 
different again. :-)

Richard