- Jan 1, 1970
I read in sci.electronics.design that Spehro Pefhany <speffSNIP@interlog
Sorry, where does 1/(N+1) come from? This 'open loop signal' is due to
the op-amp open loop gain not being infinite?
Assume all the N summing inputs save one and the output of the op-amp
are grounded (the op-amp is doing nothing). With a voltage Vin applied
to the remaining summing input, the voltage at the inverting op-amp
input is Vin* 1/(N+1). That effectively degrades the Vos, GBW, DC gain
characteristics of the op-amp by a factor of ~1/(N+1). Or to look at
it from another direction, you have a passive ~1/N attenuator followed
by a non-ideal amplifier with gain ~-N (N>>1).