IC power-supply pin
![](http://upload.wikimedia.org/wikipedia/commons/thumb/4/4b/Voltage_subscripts.png/185px-Voltage_subscripts.png)
IC power-supply pins denote a voltage and current supply terminals in
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 are V+ and V−, 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 like
For power supplies, sometimes one of the supply rails is referred to as ground (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. an audio power amplifier) the ground can be a voltage level between the most positive and most negative voltage level.
While double 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]
BJTs
ICs using bipolar junction transistors have VCC (+, positive) and VEE (-, negative) power-supply pins – though VCC is also often used for CMOS devices as well.[2]: 71
In
Resistors associated with these transistor terminals may be designated RC, RE, and RB. In order to create the DC voltages, the furthest voltage, beyond these resistors or other components if present, was often referred to as VCC, VEE, and VBB.[1] In practice VCC and VEE then refer to the positive and negative supply lines respectively in common NPN circuits.[citation needed] Note that VCC would be negative, and VEE would be positive in equivalent PNP circuits.
The VBB specifies reference bias supply voltage in ECL logic.[d]
FETs
Exactly analogous conventions were applied to field-effect transistors with their drain, source and gate terminals.[5] This led to VD and VS being created by supply voltages designated VDD and VSS in the more common circuit configurations. In equivalence to the difference between NPN and PNP bipolars, VDD is positive with regard to VSS in the case of n-channel FETs and MOSFETs and negative for circuits based on p-channel FETs and MOSFETs.
CMOS
CMOS ICs have generally borrowed the NMOS convention of VDD for positive and VSS 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 a
BJTs and FETs mixed
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 both n- and p-channel FETs. This latter case is very common in modern chips, which are often based on CMOS technology, where the C stands for complementary, meaning that complementary pairs of n- and p-channel devices are common throughout.
These naming conventions were part of a bigger picture, where, to continue with bipolar-transistor examples, although the
Similar conventions were applied to circuits involving vacuum tubes, or thermionic valves, as they were known outside of the U.S. Therefore, we see VP, VK, and VG referring to plate (or anode outside of the U.S.), cathode (note K, not C) and grid voltages in analyses of vacuum triode, tetrode, and pentode circuits.[5]
See also
- 4000 series
- 7400 series
- Bob Widlar
- Common collector
- Differential amplifier
- List of 4000 series integrated circuits
- List of 7400 series integrated circuits
- Logic family
- Logic gate
- Open collector
- Operational amplifier applications
- Pin-compatibility
- Reference designator
Notes
- ^ Regarding "voltage and current".[1]: 1-5–1-6
- ^ Used by convention.[2]: 71 [1]: 1-5–1-6
- ^ Meaning the power sourced from PSU toward power converter, like buck converter etc.
- ^ This is specifically used in TTL emitter-coupled logic (ECL) devices . The definition itself is taken from a book by Motorola on Military ECL (MECL).[1]: 15–1-6
References
- ^ OCLC 27018658.
- ^ )
- ^ Micro E, 7. Integrated circuits.
- ^ Op-amps: Some Standard Conconfigurations and Applications, Fall 2012.[permanent dead link] Washington and Lee University, Lexington, VA.
- ^ ISBN 0-471-02450-3.