[sdiy] Comparator = Opamp ??

[>>>marjan<<<]

> A comparator is a digital device that outputs a 'high' signal (logic 1 or about 4 to 5 Volts), when the voltage on the + connector is higher than the voltage on the - connector. If the one on the + is lower, it outputs a 'low' signal (logic 0 or 0 Volts).

Put in few simple words:
No, it's not "digital", it's very analog (that is if you use real
comparator not logic gate)
with "digital" logic. Internally they are somewhat like opamps, but
optimised for speed switching
between two states on/off at the output. Opamps are linear in small
range (and with feedback
we make them work in linear range for larger inputs), while comps need
very nonlinear charachteristic.
Modern comps might not have internal structure not near the opamps at
all.


> 
> An Opamp has exactly the same appearance in schematics, though i get the impression (from Circuit Maker 2000 (simulation software)) that it behaves differently. Can anyone tell me the difference, or state that they infact ARE the same...

Opamp CAN be used as comp (but not the other way), but it'll have poor
performance.
Depends on app. MS20 uses 4558 opamp for PWM but you'll find LM311
comparator in
ASM1 VCO for cap reset (here we need fast on/off to rails, speed, no
matter what
the load is etc) thou it uses TL0X2 for PWM (comparator also). Early
moogs used
real comp for PWM thou. You'll need some nice comp to clock ADC in your
digital delay
for instance. Essentially, if you're making opamp comp, you make it high
amp, 1000 
and more, to get faster transitions. Some TL0xx tend to latch in that
mode.


cheers,

marjan