好不容易找到对这些电源标号区别的详细解释，呵呵。现在网上的那些解释不是错误就是不详尽，呵呵。找个时间，把它翻译成中文的，呵呵。

Almost all integrated circuits (ICs) have at least two pins which connect to the power rails of the circuit they are installed in. These are known as the IC's power supply pins. However, the labeling of the pins varies by IC family and manufacturer.

The simplest labels are V and V−. However, internal design and historical tradition have led to a variety of other labels being used. Also, V and V− may be confused with the and − voltage inputs to ICs like op amps.

Sometimes one of the power supply pins will be referred to as ground. In digital logic, this is nearly always the negative pin; in analog integrated circuits, it is most likely to be a pin intermediate in voltage between the most positive and most negative pins ^{[citation needed]}.

Double subscript notation uses similar looking placeholders with subscripts. In that notation the subscripted letters denote two points.

History

V_CC (note: lower case is often used instead of subscript, e.g. "Vcc") is an electronics designation that refers to voltage from a power supply connected to the "collector" terminal of a bipolar transistor. In an NPN bipolar junction transistor, it would be V_CC, while in a PNP transistor, it would be −V_CC. There is debate over the origins of the double letter subscript naming convention. One proposal is that it originated as an abbreviation of the supply voltage for a common collector amplifier with the other power supply names mimicking this fashion. Double letters may also have been used to clearly indicate that a power supply voltage is being referred to.

In general, double letter subscripts refer to power supply voltages. For example, V_EE refers to the "emitter" voltage as supplied by the power supply pin. In NMOS logic, V_SS refers to the "source" voltage, and V_DD is the "drain" voltage likewise.

Within a circuit, single letter subscripts refer to that voltage relative to ground; for example, V_C is the "collector" voltage relative to ground. Two different letters indicate the voltage between two terminals; for example: V_BE is the "base" to "emitter" voltage drop, while V_CE is the "collector" to "emitter" voltage.

Modern use

CMOS ICs have generally borrowed the NMOS convention of V_DD for positive and V_SS for negative despite the fact that both positive and negative supply rails actually go to source terminals (positive supply goes to PMOS sources, negative supply to NMOS sources). ICs using bipolar transistors have V_CC (positive) and V_EE (negative) power supply pins.

In single supply systems (e.g., most modern digital and analog circuits) the negative power supply pin is also commonly referred to as GND. In "split rail" supply systems (e.g., older analog circuits) positive, negative and ground power supply pins are used.

More advanced chips will often have pins carrying voltage levels for more specialized functions in or out of the chip and these are generally labeled with some abbreviation of their purpose. For example V_BUS for the 5 volt supply needed for a bus-powered USB device or V_ref for the reference voltage for an analog-to-digital converter.

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