Hi,
What i think happened was that early circuit designers/drafters didnt
want to use terms like Vc and Vd for supply voltages because they
were already used to represent other things like Vc=Collector Voltage
and Vd=Drain Voltage, so they simply doubled the second letter so
it would not be confused with other terms.
The original motivation for Vcc was probably "Supply voltage for a
Common Collector transistor circuit" but then that idea of doubling
the second letter was probably taken further for the other terms too.
It is reasonable to do this because Vc usually means "Collector Voltage
from the Collector to ground" but was not called Vcg at that time
because it was most likely deemed too complicated for a simple
voltage like the collector voltage so Vc alone was used. This of
course meant that it could not be used for other things like supply voltage.
Same for Vd turning into Vdd and Vs turning into Vss etc.
Doubling the second letter simply shows what it is while avoiding the
possibility of confusing it with a different measurement.
For an example of a simple NPN transistor amplifier with emitter to
ground, collector to a 1k resistor and that 1k resistor to the plus
voltage supply and the base the input, the plus voltage supply
would be called "Vcc" and the voltage at the collector (referenced
to ground) would be called "Vc".
Another source of confusion then is "Vss", which could be ground
even though there is no MOSFET in this circuit, or "Vee" which
makes a little more sense. Vss would mean ground *as if* there
*were* an N-MOSFET in the circuit, even though there *is not*.
What i think happened was that early circuit designers/drafters didnt
want to use terms like Vc and Vd for supply voltages because they
were already used to represent other things like Vc=Collector Voltage
and Vd=Drain Voltage, so they simply doubled the second letter so
it would not be confused with other terms.
The original motivation for Vcc was probably "Supply voltage for a
Common Collector transistor circuit" but then that idea of doubling
the second letter was probably taken further for the other terms too.
It is reasonable to do this because Vc usually means "Collector Voltage
from the Collector to ground" but was not called Vcg at that time
because it was most likely deemed too complicated for a simple
voltage like the collector voltage so Vc alone was used. This of
course meant that it could not be used for other things like supply voltage.
Same for Vd turning into Vdd and Vs turning into Vss etc.
Doubling the second letter simply shows what it is while avoiding the
possibility of confusing it with a different measurement.
For an example of a simple NPN transistor amplifier with emitter to
ground, collector to a 1k resistor and that 1k resistor to the plus
voltage supply and the base the input, the plus voltage supply
would be called "Vcc" and the voltage at the collector (referenced
to ground) would be called "Vc".
Another source of confusion then is "Vss", which could be ground
even though there is no MOSFET in this circuit, or "Vee" which
makes a little more sense. Vss would mean ground *as if* there
*were* an N-MOSFET in the circuit, even though there *is not*.
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