Power Rails#
VCC#
Typically refers to the positive power supply rail. In most digital and analog circuits, VCC represents the positive power terminal in the circuit. VCC provides the positive voltage required by the circuit, usually used to drive transistors and integrated circuits.
VDD#
In relation to the positive power supply of VCC, VDD is more commonly used to denote the positive power pin in digital circuits. VDD is often found in integrated circuits and digital circuits, representing the positive power supply voltage required by the circuit. VDD and VCC are often used interchangeably in digital circuit design.
VEE#
Typically associated with the negative power supply. In some specific circuit designs, such as operational amplifiers and analog switches, VEE represents the negative power pin, providing the negative voltage required by the circuit, usually to extend the operational range or improve performance. The presence of VEE allows the circuit to handle negative voltage signals.
VSS#
Often denotes the ground pin or ground line. VSS is usually connected to ground, used to eliminate noise, provide reference levels, and ensure the reliability of the circuit.
Ground#
The ground line in a circuit essentially provides a low-impedance return path for the circuit. In circuit schematic design, to reduce mutual interference between circuits, different GND ground lines are generally introduced to serve as 0V reference points for different functional circuits, forming different current loops.
Analog Ground AGND#
Mainly used for the analog circuit portion, such as ADC acquisition circuits, operational amplifier circuits, etc. In these circuits, the signals are analog signals, which are weak and easily affected by large current interference from other circuits. If not distinguished, large currents can cause significant voltage drops in the analog section, leading to distortion of the analog signals and even causing the analog circuit to fail.
Digital Ground DGND#
The reason for setting up a digital ground is that digital circuits share a common characteristic of discrete signals, distinguishing only between digital 0 and 1. During the transition from digital 0 to digital 1 or vice versa, voltage changes abruptly. According to Maxwell's electromagnetic principles, changing currents generate magnetic fields around them, thus producing EMC radiation that affects other circuits.
To reduce the impact of EMC radiation on the circuit, a separate digital ground DGND must be established to effectively isolate it from other circuits.