Voltage designation

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Voltage designations that can be found in almost all circuit diagrams and in data sheets and which can be created with EDA programs are, for example, the following:

  • Positive voltage: V DD , V CC
  • Negative voltage: V SS , V EE

They originate from the English-speaking world, such as V for voltage , instead of the usual in the German and the International System of Units (SI) corresponding U (from latin urgere ) for the electrical voltage shows. Since many large semiconductor and device manufacturers come from the USA, these terms have become widespread. The index letters (often subscripted or at least shown in a smaller font size) D , S , C , and E originated from the names of the terminals (connections) of a transistor , for example drain and source ( MOSFET ) and collector , emitter ( bipolar transistor ) . Double indices such as CC or DD usually stand for the supply voltages to ground.

Specific names

The double indexing is in most cases a plural formation , that is, a generalization. So it is not about the voltage on a single specific pin of the component . For example, V CC originally referred to the collector voltages on several components. Absolute distinctions between these voltage designations, for example between V CC and V DD , have been blurred since the alternate / simultaneous use of TTL logic and CMOS logic .

Here are some of the most common names at a glance:

  • V B - voltage at the base
  • V BB - connection of the bulks (wells) of the MOSFETs, mostly −5 V, so not the voltage at the base pins of several transistors!
  • V BAT - battery voltage
  • V BE - voltage between base and emitter for bipolar transistors
  • V C - is the voltage at the collector of a bipolar transistor
  • V CC - plural formation: voltage at the collectors, positive supply voltage for bipolar ICs
  • V CE - voltage between collector and emitter for bipolar transistors
  • V CEsat - voltage between C and E when the transistor is saturated
  • V CM - mean voltage of integrated circuits with asymmetrical power supply
  • V core - the power supply for the "important" chips such as CPU or GPU
  • V D - voltage at the drain of an FET
  • V DS - voltage between drain and source in FETs
  • V DD - positive supply voltage of MOS circuits (the place where many "drains" of the NMOS logic hang)
  • V DDQ - The power supply for the output buffer of a memory chip
  • V E - voltage at the emitter
  • V EE - voltage at the emitters, negative supply voltage e.g. B. ECL ICs
  • V G - voltage at the gate
  • V DC - voltage between gate and source in FETs
  • V IN - input voltage
  • V MEM - The power supply for a mem ory chip / memory chip, sometimes: V DDR , V DIMM or similar
  • V OUT - output voltage
  • V PP - voltage difference between positive and negative peak voltage (peak to peak), but also programming voltage for (E) EPROMs and microcontrollers
  • V REF - reference voltage
  • V RMS - root mean square , effective value of a voltage
  • V S - voltage at source
  • V SS - negative supply voltage of MOS circuits, often identical to GND (see below)
  • V TT - connection of the terminating resistors (terminators)

General terms

There are also more general terms for positive and negative supply voltages, such as B .:

  • V + - positive supply voltage (does not say anything about the voltage level!)
  • V ++ - positive supply voltage (does not say anything about the voltage level!)
  • V - - negative supply voltage
  • V −− - negative supply voltage
  • GND - 0 V, 0 potential, ground , abbreviation for English. "Ground". The voltage or "potential difference" is measured against this potential. The voltage potential of positive voltages is higher than GND, negative voltages have a voltage potential that is below GND. Colloquially, GND is often incorrectly referred to as negative supply voltage. An applied (positive or negative) current flows back to the voltage source via the GND line .
  • CGND - "Chassis-Ground" - which is usually the case connected
  • SGND - "Signal-Ground" - often used for negative voltage levels in analog circuit parts, e.g. B. Audio
  • DGND - "Digital Ground" - in connection with digital modules with an analog input
  • AGND - "Analog-Ground" - analog signals in digital components often have a separate ground

The problem with this name assignment is: It is only a question of names , and by no means binding standards or norms . When assigning such names in the circuit diagram design , great care should always be exercised, and new or additional names should only be introduced if the relevant supply voltage is actually physically decoupled from other voltages in the circuit (for example via a choke coil ) and if it is used on several component pins.