Re: History of decoupling capacitors

From: fcweed (fcweed_at_mail.com)
Date: 06/25/04 

Date: Thu, 24 Jun 2004 23:28:33 -0500

Joerg wrote:
> Hi Theo,
>
> Nowadays the word "decoupling" is use to describe decoupling current
> spikes from the power supply. IOW to prevent them from entering there or
> causing a momentary sag in voltage.
>
> In the olden days the word also meant decoupling one stage from another,
> for example the plate DC level from the much lower gate DC bias of the
> next amplifier stage. In that respect they are really historic. Even the
> vintage telephones with cranks and separate ear pieces had a decoupling
> cap. They just didn't call it capacitor but condenser.
>

Where I grew up, we used the terms "decoupling" and "bypass" capacitors,
where the latter provided a noise glitch bypass from power to ground.

wrt. the original question, bypass/decoupling caps for digital circuits
were already necessary with RTL. The first flip-flop circuit we built in
the first digital logic course I took was a simple 4-stage ripple
counter - Not much to screw up, but it didn't work. The instructor
didn't even look at the circuit wiring, he just clipped a small cap
between power and ground and things worked as expected - Which may have
been the real point of the whole exercise. 

-- 
------------------------------------
best regards,
fcweed               fcweed@mail.com

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