Drift of high/low input signal threshold in CD4000-series digital ICs ?

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Alec_t

Joined Sep 17, 2013
13,153
I'm aware that the signal input threshold of CMOS ICs in the CD4000 series is approximately half the supply voltage (ignoring Schmitt inputs), but varies from chip to chip due to manufacturing tolerances. That said, supposing for argument's sake the threshold of a given IC were exactly 50% at 25C, how much would it be expected to vary over a temp range of, say, -40C to +40C ? I can't find info on threshold drift with temperature in datasheets. Would it depend on the particular topology of the PMOS and NMOS devices within the IC ? Would drift of some PMOS devices parially cancel out drift of some NMOS devices ?
 

crutschow

Joined Mar 14, 2008
30,791
Because I want to use a simple logic gate (rather than a 'proper' comparator) in a minimal-cost timing circuit, to sense when a ramp voltage crosses the threshold.
You do realize that, if the gate doesn't have a Schmidt-trigger input, it may oscillator as the ramp reaches the threshold voltage?
 
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