Vcc, Vdd, Vss, etc.

http://encyclobeamia.solarbotics.net/articles/vxx.html

These notations are used in describing voltages at various common power supply terminals (at these points, only a wire lead exists between the point and a power source) of a given circuit. It turns out that these common voltage terms map to transistor technology as follows:

BJT	FET	"Vxx" meaning
Vcc	Vdd	Positive supply voltage
Vee	Vss	Negative supply, ground

Apparently this terminology originated in some way from the terminals of each type of transistor, and their common connections in logic circuits (i.e., Vcc is often applied to BJT collectors, Vee to BJT emitters, Vdd to FET drains, and Vss to FET sources). This notation then carries across to integrated circuits -- TTL ICs were originally based on BJT technology, and so often use the Vcc / Vee terminology; CMOS ICs are based on FET technology, and so often use the Vdd / Vss terminology.

The absolute distinctions between these common supply terms has since been blurred by the interchangeable application of TTL and CMOS logic families. Most CMOS (74HC / AC, etc.) IC data sheets now use Vcc and Gnd to designate the positive and negative supply pins.

http://bbs.ednchina.com/?url=http://bbs.ednchina.com/ShowTopic.aspx?id=19053

在电子电路中，常可以看到VCC、VDD和VSS三种不同的符号，它们有什么区别呢？

一、解释

VCC：C=circuit 表示电路的意思, 即接入电路的电压；

VDD：D=device 表示器件的意思, 即器件内部的工作电压；

VSS：S=series 表示公共连接的意思，通常指电路公共接地端电压。

二、说明

1、对于数字电路来说，VCC是电路的供电电压,VDD是芯片的工作电压（通常Vcc>Vdd），VSS是接地点。

2、有些IC既有VDD引脚又有VCC引脚，说明这种器件自身带有电压转换功能。

3、在场效应管（或COMS器件）中，VDD为漏极，VSS为源极，VDD和VSS指的是元件引脚，而不表示供电电压。