SEM VCO buffer

[Martin Czech]

:::	>Another idea is to use a CMOS logic Schmitt trigger IC.  One of the
:::faster
:::	>logic familys. 
:::
:::The ARP Odyssey uses a CMOS gate to detect the threshold (no schmitt
:::trigger, though).
:::
:::How are CMOS schmitt trigger made (internally), btw ?
:::I know how to configure one from two inverters and two resistors, but I
:::have no idea how the genuine CMOS schmitt triggers are made.
:::

Juergen,

the two inverters/two resistors type is the typical kind of circuit we
find in books only. In reality (at least in ICs) something different is
used (no good resistors in CMOS logic process).  It is a design that is
copied now for ages, nothing sophisticated, just 2x3 MOSFETS and maybe
another 2 for a buffer.

If you have an old CMOS CD40xx databook I'm sure that you'll find the
schematic there. The feedback is done via currents. This simple circuit
is very dependend on Vdd (no problem) but no much on temperature (which
is good).


m.c.