[sdiy] Can google's free* 180nm OSHW foundry be used for synth parts?

[ASSI]

On Samstag, 6. August 2022 22:41:52 CEST Mike Bryant wrote:
> I wonder if a CMOS equivalent to an OTA could be designed with CMOS
> transistors and an input resistor ?  Any thoughts ?

Yes, they even use the same topology.  It's in a way even easier than the 
bipolar version since there's no error from the base current.  The caveat is 
that the governing law of the translinear loop is now sqrt rather then exp and 
that makes for a much smaller linear range.  It can be extended by adding more 
transistors and bias sources of course, but it's getting complicated fast.  
You can operate in subthreshold instead and get the exp behaviour back, but of 
course in a MOS that still doesn't extend the same number of decades as it 
does in a bipolar transistor.

The other thing that lots of people don't get about modern IC process 
technology is that the transistors are as cheap as they get (that's the whole 
point of th exercise), but any passive devices are going to be much more 
expensive (if available at all).  Continous time analog filters in the audio 
range are prohibitively expensive or impossible to implement.


Regards,
Achim.
-- 
+<[Q+ Matrix-12 WAVE#46+305 Neuron microQkb Andromeda XTk Blofeld]>+

Waldorf MIDI Implementation & additional documentation:
http://Synth.Stromeko.net/Downloads.html#WaldorfDocs