IC power-supply pins are voltage and current supply terminals found onintegrated circuits (ICs) inelectrical engineering,electronic engineering, andintegrated circuit design.[a] ICs have at least two pins that connect to thepower rails of the circuit in which they are installed. These are known as thepower-supply pins. However, the labeling of the pins varies by IC family and manufacturer. The double-subscript notation usually corresponds to a first letter in a given IC family (transistors) notation of the terminals (e.g. VDD supply for a drain terminal in FETs etc.).
| NPN BJT[b] | N-FET | AC/DC[c] | DC | DC | |||
|---|---|---|---|---|---|---|---|
| Positive supply voltage | VCC/VBB | VDD | V+ | VS+ | VIN | VDD | VA |
| Negative supply voltage | VEE | VSS | V− | VS− | |||
| Ground | GND | GND | 0 | 0 | GND | GND | GND |
The simplest labels areV+ andV−, but internal design and historical traditions have led to a variety of other labels being used. V+ and V− may also refer to the non-inverting (+) and inverting (−) voltage inputs of ICs likeop amps.
For power supplies, sometimes one of the supply rails is referred to asground (abbreviated "GND") – positive and negative voltages are relative to the ground. In digital electronics, negative voltages are seldom present, and the ground nearly always is the lowest voltage level. In analog electronics (e.g. anaudio power amplifier) the ground can be a voltage level between the most positive and most negative voltage level.
Whiledouble-subscript notation, where subscripted letters denote the difference between two points, uses similar-looking placeholders with subscripts, the double-letter supply voltage subscript notation is not directly linked (though it may have been an influencing factor).[3][4]
ICs usingbipolar junction transistors haveVCC (+, positive) andVEE (-, negative) power-supply pins – thoughVCC is also often used for CMOS devices as well.[2]: 71
Incircuit diagrams and circuit analysis, there are long-standing conventions regarding the naming of voltages, currents, and some components.[5] In the analysis of a bipolar junction transistor, for example, in acommon-emitter configuration, theDC voltage at the collector, emitter, and base (with respect to ground) may be written asVC,VE, andVB respectively.
Resistors associated with these transistor terminals may be designatedRC,RE, andRB. In order to create the DC voltages, the furthest voltage, beyond these resistors or other components if present, was often referred to asVCC,VEE, andVBB.[1] In practiceVCC andVEE then refer to the positive and negative supply lines respectively incommonNPN circuits.[citation needed] Note thatVCC would be negative, andVEE would be positive in equivalentPNP circuits.
TheVBB specifiesreference bias supply voltage in ECL logic.[d]
Exactly analogous conventions were applied tofield-effect transistors with their drain, source and gate terminals.[5] This led toVD andVS being created by supply voltages designatedVDD andVSS in themore common circuit configurations. In equivalence to the difference between NPN and PNP bipolars,VDD is positive with regard toVSS in the case ofn-channelFETs andMOSFETs and negative for circuits based onp-channel FETs and MOSFETs.
CMOS ICs have generally borrowed the NMOS convention ofVDD for positive andVSS for negative, even though both positive and negative supply rails connect to source terminals (the positive supply goes to PMOS sources, the negative supply to NMOS sources).
In many single-supply digital and analog circuits the negative power supply is also called "GND". In "split-rail" supply systems there are multiple supply voltages. Examples of such systems include modern cell phones, with GND and voltages such as 1.2 V, 1.8 V, 2.4 V, 3.3 V, and PCs, with GND and voltages such as −5 V, 3.3 V, 5 V, 12 V. Power-sensitive designs often have multiple power rails at a given voltage, using them to conserve energy by switching off supplies to components that are not in active use.
More advanced circuits often have pins carrying voltage levels for more specialized functions, and these are generally labeled with some abbreviation of their purpose. For example, VUSB for the supply delivered to aUSB device (nominally 5 V), VBAT for a battery, or Vref for the reference voltage for ananalog-to-digital converter. Systems combining both digital and analog circuits often distinguish digital and analog grounds (GND and AGND), helping isolate digital noise from sensitive analog circuits. High-security cryptographic devices and other secure systems sometimes require separate power supplies for their unencrypted and encrypted (red/black) subsystems to prevent leakage of sensitive plaintext.
Although still in relatively common use, there is limited relevance of these device-specific power-supply designations in circuits that use a mixture of bipolar and FET elements, or in those that employ either both NPN and PNP transistors or bothn- andp-channel FETs. This latter case is very common in modern chips, which are often based onCMOS technology, where theC stands forcomplementary, meaning that complementary pairs ofn- andp-channel devices are common throughout.
These naming conventions were part of a bigger picture, where, to continue with bipolar-transistor examples, although theFET remains entirely analogous,DC orbias currents into or out of each terminal may be writtenIC,IE, andIB. Apart from DC or bias conditions, many transistor circuits also process a smaller audio-, video-, or radio-frequency signal that is superimposed on the bias at the terminals. Lower-case letters and subscripts are used to refer to these signal levels at the terminals, eitherpeak-to-peak orRMS as required. So we seevc,ve, andvb, as well asic,ie, andib. Using these conventions, in a common-emitter amplifier, the ratiovc/vb represents the small-signal voltage gain at the transistor, andvc/ib the small-signaltrans-resistance, from which the nametransistor is derived by contraction. In this convention,vi andvo usually refer to the external input and output voltages of the circuit or stage.[5]
Similar conventions were applied to circuits involvingvacuum tubes, orthermionic valves, as they were known outside of the U.S. Therefore, we seeVP,VK, andVG referring to plate (oranode outside of the U.S.), cathode (noteK, notC) and grid voltages in analyses of vacuumtriode,tetrode, andpentode circuits.[5]
{{cite book}}: CS1 maint: location missing publisher (link)