[sdiy] Re: 4007 Voltage Controlled State Variable Filter (off list)

[ASSI]

On Tuesday 17 February 2004 23:31, Magnus Danielson wrote:
> Yeah, I've long known this, but what is the main reason that we don't
> see these 4 pins on trannies.

Single transistors are mostly made in a bulk process, not planar like 
it is the case for IC. This cuts down on the number of masking steps, 
but precludes the possibility to seperately connect the substrate.

> What ugly trick do you do up there on the chip when you do
> full-custom anyway?

Simple: more masking steps and additional implants to bring the bulk 
contact up to the surface and isolate it from the substrate. But that 
is standard and I can't tell you about the really ugly tricks... but if 
you look around you may still find them. :-)


Achim.
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