Question about core sense amplifiers

[Brent Hilpert]

On 2015-Mar-10, at 8:08 AM, Vincent Slyngstad wrote:

> I've got a technical question about core memories.  I've been looking, in particular, at the MC1540G sense amplifier.  There's an external capacitor that is supposed to be connected between pins 1 and 10 (it looks like about .01uF was traditional).  Maybe I'm being thick this week, but I don't quite get what this does for the circuit.  It's part of the "DC restoration" section.
> 
> I think I have some idea what amplification and slicing mean in this context, but "DC restoration" isn't firing any neurons.
> 
> Can any of you that have studied how core works help me understand this?

Looking at the 1540 internals schematic, it looks like a frequency compensation capacitor.

Early op amps like the 709 required external capacitors for freq. comp.
Core sense amps are essentially a form of voltage comparator adapted to respond to the absolute value of a differential input (produce the same output for a voltage difference of either polarity at the inputs), and voltage comparators in turn are essentially op-amps running open-loop.

(if that helps any . . )