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Letter Symbols - Transistors General
LETTER SYMBOLS
The letter symbols for transistors detailed in this section
are based on IEC publication number 148.
Letter symbols for currents, voltages and powers
BASIC LETTERS
I, i current
V, v voltage
P, p power.
Upper-case letter symbols are used to represent all values
except instantaneous values that vary with time, these are
represented by lower-case letters.
SUBSCRIPTS
A, a anode terminal
(AV), (av) average value
B, b base terminal
C, c collector terminal
D, d drain terminal
E, e emitter terminal
F, f forward
G, g gate terminal
K, k cathode terminal
M, m peak value
O, o as third subscript: the terminal not
mentioned is open-circuit
R, r as first subscript: reverse. As second
subscript: repetitive. As third subscript: with
a specified resistance between the terminal
not mentioned and the reference terminal
(RMS), (rms) root-mean-square value
S, s as first or second subscript: source terminal
(FETs only). As second subscript:
non-repetitive (not FETs). As third subscript:
short circuit between the terminal not
mentioned and the reference terminal
X, x specified circuit
Z, z replaces R to indicate the actual working
voltage, current or power of voltage
reference and voltage reference diodes.
No additional subscript is used for DC values.
Upper-case subscripts are used for the indication of:
Continuous (DC) values (without signal), e.g. IB
Instantaneous total values, e.g. iB
Average total values, e.g. IB(AV)
Peak total values, e.g. IBM
Root-mean-square total values, e.g. IB(RMS).
Lower-case subscripts are used for the indication of values
applying to the varying component alone:
Instantaneous values, e.g. ib
Root-mean-square values, e.g. Ib(rms)
Peak values, e.g. Ibm
Average values, e.g. Ib(av).
If more than one subscript is used, the subscript for which
both styles exist are either all upper-case or all lower-case.
ADDITIONAL RULES FOR SUBSCRIPTS
Transistor currents
If it is necessary to indicate the terminal carrying the
current, this should be done by the first subscript
(conventional current flow from the external circuit into the
terminal is positive).
Examples: IB, iB, ib, Ibm.
Transistor voltages
If it is necessary to indicate the points between which a
voltage is measured, this should be done by the first two
subscripts. The first subscript indicates the terminal at
which the voltage is measured and the second the
reference terminal or the circuit node. Where there is no
possibility of confusion, the second subscript may be
omitted.
Examples: VBE, vBE, vbe, Vbem.
Supply voltages or currents
Supply voltages or supply currents are indicated by
repeating the appropriate terminal subscript.
Examples: VCC, IEE.
If it is necessary to indicate a reference terminal, this
should be done by a third subscript.
Example: VCCE.
Subscripts for devices with more than one terminal of the
same kind
If a device has more than one terminal of the same kind,
the subscript is formed by the appropriate letter for the
terminal, followed by a number. In the case of multiple
subscripts, hyphens may be necessary to avoid confusion.
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Philips Semiconductors
Letter Symbols - Transistors General
Examples:
IB2 continuous (DC) current flowing into the second
base terminal
VB2-E continuous (DC) voltage between the terminals of
second base and emitter terminals.
Subscripts for multiple devices
For multiple unit devices, the subscripts are modified by a
number preceding the letter subscript. In the case of
multiple subscripts, hyphens may be necessary to avoid
confusion.
Examples:
I2C continuous (DC) current flowing into the collector
terminal of the second unit
V1C-2C continuous (DC) voltage between the collector
terminals of the first and second units.
Application of the rules
Figure 1 represents a transistor collector current as a
function of time. It comprises a continuous (DC) current
and a varying component.
Letter symbols for electrical parameters
DEFINITION
For the purpose of this publication, the term ‘electrical
parameter’ applies to four-pole matrix parameters,
elements of electrical equivalent circuits, electrical
Fig.1 Collector current as a function of time.
MBD537
collector
current
0
IC
(no signal)
IC(RMS)
Ic(av)
ICM
ic
ic
Ic(rms)
Icm
IC(AV)
time
impedances and admittances, inductances and
capacitances.
BASIC LETTERS
The following list comprises the most important basic
letters used for electrical parameters of semiconductor
devices.
B, b susceptance (imaginary part of an admittance)
C capacitance
G, g conductance (real part of an admittance)
H, h hybrid parameter
L inductance
R, r resistance (real part of an impedance)
X, x reactance (imaginary part of an impedance)
Y, y admittance
Z, z impedance.
Upper-case letters are used for the representation of:
Electrical parameters of external circuits and of circuits
in which the device forms only a part
All inductances and capacitances.
Lower-case letters are used for the representation of
electrical parameters inherent in the device, with the
exception of inductances and capacitances.
SUBSCRIPTS
General subscripts
The following list comprises the most important general
subscripts used for electrical parameters of semiconductor
devices.
F, f forward (forward transfer)
I, i (or 1) input
L, l load
O, o (or 2) output
R, r reverse (reverse transfer)
S, s source.
Examples: Zs, hf, hF.
The upper-case variant of a subscript is used for the
designation of static (DC) values.
Examples:
hFE static value of forward current transfer ratio in
common-emitter configuration (DC current gain)
REDC value of the external emitter resistance.
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Letter Symbols - Transistors General
The static value is the slope of the line from the origin to
the operating point on the appropriate characteristic curve,
i.e. the quotient of the appropriate electrical quantities at
the operating point.
The lower-case variant of a subscript is used for the
designation of small-signal values.
Examples:
hfe small-signal value of the short-circuit
forward current transfer ratio in
common-emitter configuration
Ze=R
e+jX
esmall-signal value of the external
impedance.
If more than one subscript is used, subscripts for which
both styles exist are either all upper-case or all lower-case.
Examples: hFE, yRE, hfe.
Subscripts for four-pole matrix parameters
The first letter subscript (or double numeric subscript)
indicates input, output, forward transfer or reverse
transfer.
Examples: hi (or h11), ho (or h22), hf (or h21), hr (or h12).
A further subscript is used for the identification of the circuit
configuration. When no confusion is possible, this further
subscript may be omitted.
Examples: hfe (or h21e), hFE (or h21E).
DISTINCTION BETWEEN REAL AND IMAGINARY PARTS
If it is necessary to distinguish between real and imaginary
parts of electrical parameters, no additional subscripts
should be used. If basic symbols for the real and imaginary
parts exist, these may be used.
Examples: Zi=R
i+jX
i
,y
fe =g
fe +jb
fe.
If such symbols do not exist, or if they are not suitable, the
following notation is used:
Examples:
Re (hib) etc. for the real part of hib
Im (hib) etc. for the imaginary part of hib.