IC power supply pin
Encyclopedia
Almost all integrated circuit
s (ICs) have at least two pins that connect to the power rails of the circuit in which they are installed. 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−, but internal design and historical traditions have led to a variety of other labels being used. V+ and V− may also refer to the inverting (−) and non-inverting (+) voltage inputs of ICs like op amps.
Sometimes one of the power supply pins will be referred to as ground
(abbreviated "GND"). 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 .
Double subscript notation
uses similar looking placeholders with subscripts. In that notation the subscripted letters denote two points.
, for example in a common emitter
configuration, the DC voltage at the collector, emitter, and base (with respect to ground) may be written as VC, VE and VB respectively. 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. In practice VCC and VEE then refer to the plus and minus supply lines respectively in common
NPN circuits. Note that VCC would be negative and VEE would be positive in equivalent PNP circuits.
Exactly analogous conventions were applied to field-effect transistor
s with their drain, source and gate terminals. 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.
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 FET remains entirely analogous, DC or bias currents into or out of each terminal may be written IC, IE and IB. 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, either peak-to-peak or rms
as required. So we see vc, ve and vb as well as ic, ie and ib. Using these conventions, in a common emitter amplifier, the ratio vc/vb represents the small-signal voltage gain at the transistor and vc/ib the small-signal trans-resistance from which the name transistor is derived by contraction. In this convention, vi and vo usually refer to the external input and output voltages of the circuit or stage.
Similar conventions were applied to circuits involving vacuum tube
s 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.
ICs have generally borrowed the NMOS convention of VDD for positive and VSS 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 VCC (positive) and VEE (negative) power supply pins.
In single supply systems (e.g., many simple digital and analog circuits) the negative power supply is also commonly referred to as 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 which are not in active use.
More advanced circuits will 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 USB device (nominally 5 V), VBAT for a battery, or Vref for the reference voltage for an analog-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.
Integrated circuit
An integrated circuit or monolithic integrated circuit is an electronic circuit manufactured by the patterned diffusion of trace elements into the surface of a thin substrate of semiconductor material...
s (ICs) have at least two pins that connect to the power rails of the circuit in which they are installed. These are known as the IC's power supply pins. However, the labeling of the pins varies by IC family and manufacturer.
| Typical supply pin labeling | ||||
|---|---|---|---|---|
| BJT Bipolar junction transistor |- align = "center"| || PNP|- align = "center"| || NPNA bipolar transistor is a three-terminal electronic device constructed of doped semiconductor material and may be used in amplifying or switching applications. Bipolar transistors are so named because their operation involves both electrons... |
FET | |||
| VCC | VDD | V+ | VS+ | Positive supply voltage |
| VEE | VSS | V− | VS− | Negative supply voltage |
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 inverting (−) and non-inverting (+) voltage inputs of ICs like op amps.
Sometimes one of the power supply pins will be referred to as ground
Ground (electricity)
In electrical engineering, ground or earth may be the reference point in an electrical circuit from which other voltages are measured, or a common return path for electric current, or a direct physical connection to the Earth....
(abbreviated "GND"). 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 .
Double subscript notation
Double subscript notation
In engineering, double-subscript notation is notation used to indicate some variable between two points...
uses similar looking placeholders with subscripts. In that notation the subscripted letters denote two points.
History
In circuit diagrams and circuit analysis, there are long-standing conventions regarding the naming of voltages, currents and some components. In the analysis of a bipolar junction transistorBipolar junction transistor
|- align = "center"| || PNP|- align = "center"| || NPNA bipolar transistor is a three-terminal electronic device constructed of doped semiconductor material and may be used in amplifying or switching applications. Bipolar transistors are so named because their operation involves both electrons...
, for example in a common emitter
Common emitter
In electronics, a common-emitter amplifier is one of three basic single-stage bipolar-junction-transistor amplifier topologies, typically used as a voltage amplifier...
configuration, the DC voltage at the collector, emitter, and base (with respect to ground) may be written as VC, VE and VB respectively. 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. In practice VCC and VEE then refer to the plus and minus supply lines respectively in common
Common emitter
In electronics, a common-emitter amplifier is one of three basic single-stage bipolar-junction-transistor amplifier topologies, typically used as a voltage amplifier...
NPN circuits. Note that VCC would be negative and VEE would be positive in equivalent PNP circuits.
Exactly analogous conventions were applied to field-effect transistor
Field-effect transistor
The field-effect transistor is a transistor that relies on an electric field to control the shape and hence the conductivity of a channel of one type of charge carrier in a semiconductor material. FETs are sometimes called unipolar transistors to contrast their single-carrier-type operation with...
s with their drain, source and gate terminals. This led to VD and VS being created by supply voltages designated VDD and VSS in the more common circuit configurations
Common source
In electronics, a common-source amplifier is one of three basic single-stage field-effect transistor amplifier topologies, typically used as a voltage or transconductance amplifier. The easiest way to tell if a FET is common source, common drain, or common gate is to examine where the signal...
. 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.
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
CMOS
Complementary metal–oxide–semiconductor is a technology for constructing integrated circuits. CMOS technology is used in microprocessors, microcontrollers, static RAM, and other digital logic circuits...
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 FET remains entirely analogous, DC or bias currents into or out of each terminal may be written IC, IE and IB. 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, either peak-to-peak or rms
Root mean square
In mathematics, the root mean square , also known as the quadratic mean, is a statistical measure of the magnitude of a varying quantity. It is especially useful when variates are positive and negative, e.g., sinusoids...
as required. So we see vc, ve and vb as well as ic, ie and ib. Using these conventions, in a common emitter amplifier, the ratio vc/vb represents the small-signal voltage gain at the transistor and vc/ib the small-signal trans-resistance from which the name transistor is derived by contraction. In this convention, vi and vo usually refer to the external input and output voltages of the circuit or stage.
Similar conventions were applied to circuits involving vacuum tube
Vacuum tube
In electronics, a vacuum tube, electron tube , or thermionic valve , reduced to simply "tube" or "valve" in everyday parlance, is a device that relies on the flow of electric current through a vacuum...
s 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
Triode
A triode is an electronic amplification device having three active electrodes. The term most commonly applies to a vacuum tube with three elements: the filament or cathode, the grid, and the plate or anode. The triode vacuum tube was the first electronic amplification device...
, tetrode
Tetrode
A tetrode is an electronic device having four active electrodes. The term most commonly applies to a two-grid vacuum tube. It has the three electrodes of a triode and an additional screen grid which significantly changes its behaviour.-Control grid:...
and pentode
Pentode
A pentode is an electronic device having five active electrodes. The term most commonly applies to a three-grid vacuum tube , which was invented by the Dutchman Bernhard D.H. Tellegen in 1926...
circuits.
Modern use
CMOSCMOS
Complementary metal–oxide–semiconductor is a technology for constructing integrated circuits. CMOS technology is used in microprocessors, microcontrollers, static RAM, and other digital logic circuits...
ICs have generally borrowed the NMOS convention of VDD for positive and VSS 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 VCC (positive) and VEE (negative) power supply pins.
In single supply systems (e.g., many simple digital and analog circuits) the negative power supply is also commonly referred to as 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 which are not in active use.
More advanced circuits will 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 USB device (nominally 5 V), VBAT for a battery, or Vref for the reference voltage for an analog-to-digital converter
Analog-to-digital converter
An analog-to-digital converter is a device that converts a continuous quantity to a discrete time digital representation. An ADC may also provide an isolated measurement...
. 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
RED/BLACK concept
The RED/BLACK concept refers to the careful segregation in cryptographic systems of signals that contain sensitive or classified plaintext information from those that carry encrypted information, or ciphertext ....
) subsystems to prevent leakage of sensitive plaintext.