Another question about core sense amplifiers

[Jon Elson]

On 03/11/2015 12:45 PM, Rick Bensene wrote:
> OK, while we're on the topic of core memory sense circuitry, in some of
> the old calculators that I've come across (a good example being the
> Casio AL-1000 -- http://oldcalculatormuseum.com/al1kck10l.html) ) there
> are transformers (pulse transformers) in the core memory sense
> circuitry.  What purpose would these serve, and why are they used in
> some core memory applications, and not in others? In the case of the
> AL-1000, similar transformers are used in the X-Y drivers as well.
>
>
I think most core memories that use the 3-wire scheme use 
transformers to
couple the sense amps.  The older, 4-wire scheme used 
separate wires for the
inhibit wire and the sense wire.  When merging those (which 
allowed smaller
cores, thus faster cycle time) you had a bunch of driver 
transistors attached to
the sense/inhibit winding, which may have unbalanced the 
line, affecting the
balance of the sense amp.   Well, I think that is somewhat 
close to the
reason for them.

Jon