![]() ![]() So V CCB means the DC supply voltage at the semiconductor device's Collector in reference to the device's Base and V CC means the DC supply voltage at the Collector in reference to ground.Īt first instinct it would seem that the reduplication of the subscript would lead to ambiguity, but in fact it doesn't. ![]() Now for the extra credit: Why V CC instead of V C or V DD instead of V D? I used to think that it's colloquial from "Voltage from Collector to Collector" but obviously it's no surprise that it's also defined in the standard: The DC or RMS voltage at the base is V B and an instantaneous voltage at the base is v b. In case the said semiconductor's emitter is directly connected to ground, which is certainly understood to be a known reference, then the AC RMS voltage at the base is V b. So for example V bE means the RMS value (capital V) of the AC component (lower case b) of the Voltage at the Base of a semiconductor device in reference to the DC value of the Voltage of the semiconductor device's Emitter (upper case E). Paragraph 1.3 defines how subscripts are written, especially when there is more than one. It's amazing how all this has become common knowledge that is now quietly accepted and understood even without a normative reference. The further nuances of the standard, that define further rules on how the symbols are written makes for fascinating reading. It has since been superseded by a newer standard that defines the letters for Drain and Source, but I don't have that standard available. This standard predates the MOS transistor (which was patented in August 1963) and thus doesn't have the letters for Source and Drain. J, j for a generic semiconductor device terminal.The standard defines 11 suffix (letter)s. Supply voltages are obviously DC voltages, so their letters must be in upper case. Subscript letters in upper case mean DC values and lower case mean AC values. Paragraph 1.2 starts to define the subscripts for quantity symbols. I'm an electronics history fanatic and this might be interesting to other (fanatic)s, so I'll make this answer a bit broader than necessary.įirst of all, the first letter capital V comes from the standard's paragraphs 1.1.1 and 1.1.2, which define that v and V are quantity symbols describing voltage in lower case it means instantaneous voltage (1.1.1) and in upper case it means maximum, average or RMS voltage (1.1.2). This naming comes from a 1963 IEEE standard 255-1963 "Letter Symbols for Semiconductor Devices" (IEEE Std 255-1963). I think I may have the definite answer to this. Technically Vcc/Vee is for bipolar and Vdd/Vss for FETs, but in practise today Vcc and Vdd mean the same, and Vee and Vss mean the same. ![]() However, the Vdd and Vss names have stuck for historical reasons. With roughly equal numbers of N and P channel devices, drains aren't more likely to be positive than sources, and vice versa. A CMOS inverter is just a P channel and a N channel MOSFET in its simplest form. That means both N and P channel devices are used in about equal numbers. Note that the "C" in CMOS stands for "complementary". With CMOS this makes no sense, but it persists anyway. When FET logic came about, the same kind of naming was used, but now the positive supply was Vdd (drain) and the negative Vss (source). Sometimes (but less commonly) the negative supply was called Vee where "e" stands for emitter. Back then it made sense to someone that the positive supply voltage would be called Vcc where the "c" stands for collector. Even more specifically, they were NPN because for some reasons I'm not going to get into, NPN were faster. Back in the pleistoscene (1960s or earlier), logic was implemented with bipolar transistors. ![]()
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