Really OLD logic levels

[whit3rd]

Today we use LVD (low voltage differential) logic, at low voltage levels; before
that, there was HVD (RS-485), ECL, TTL, DTL, and a few odd items
like the high-voltage DTL of MC1488, and CML (current-mode
logic?) and such.

But 'WAY back there was a system with high power supply voltages
(about 450V) and very peculiar antenna-based sensing

<http://phenomena.nationalgeographic...ees-can-move-each-other-with-electric-fields/>

 

[[email protected]]

Today we use LVD (low voltage differential) logic, at low voltage levels; before
that, there was HVD (RS-485), ECL, TTL, DTL, and a few odd items
like the high-voltage DTL of MC1488, and CML (current-mode
logic?) and such.

Don't forget the high threshold logic families (15 V) used in
industrial applications.

But 'WAY back there was a system with high power supply voltages
(about 450V) and very peculiar antenna-based sensing

Why would anyone use such high voltages for digital logic ? This
would require quite high impedance levels and due to the stray
capacitances, quite slow operation.

For instance the 5965 double triode was operated at about 100-150 V
anode voltage supply. The early semiconductor diodes used to build
diode/tube logic NAND/NOR would not have tolerated much more.

As strange as it might sound, the early semiconductor diodes were more
unreliable than tubes.

 

[Tim Williams]

Don't forget the high threshold logic families (15 V) used in
industrial applications.

I've never heard anything about vacuum state logic levels, if any
companies even defined their own logic standards -- I would guess
something in the neighborhood of, say, -20/0V (requires low current C-
supply) or 50/100V (requires cathode bias = wastes power).

Tubes aren't so bad. I've done, I think it was -80/0V drive into a sweep
tube, which is equivalent of driving a 6000V, 1A MOSFET to produce
sub-150ns edges (comparable to... lazily driving an IRF540, I'd say).
Such high voltage MOSFETs don't even exist [yet], so I guess toobs win
that battle.

Why would anyone use such high voltages for digital logic ?

Umm, read the link..

Tim

 

[gregz]

Today we use LVD (low voltage differential) logic, at low voltage levels; before
that, there was HVD (RS-485), ECL, TTL, DTL, and a few odd items
like the high-voltage DTL of MC1488, and CML (current-mode
logic?) and such.

But 'WAY back there was a system with high power supply voltages
(about 450V) and very peculiar antenna-based sensing

<http://phenomena.nationalgeographic...ees-can-move-each-other-with-electric-fields/>

I worked with stuff negative voltage, even saw negative logic
Collins logic, dec logic, zerox logic, general dynamics dynamic logic.

Greg

 

[whit3rd]

On Thu, 4 Apr 2013 14:27:35 -0700 (PDT), whit3rd <[email protected]>

wrote:

Why would anyone use such high voltages for digital logic ?

It was because the power supplies (highly redundant, a system would operate
with a few hundred of 'em) weren't regulated, except by corona leakage to atmosphere.

Higher tech for regulators (gas discharge tubes, Zener diodes, bandgap references)
was unavailable.