Note: the following terms are defined in the
context of function generators. Some may
have additional meaning in other areas of
electronics.
AM (Amplitude Modulation) - The process
of varying the amplitude of one signal in
accordance with the amplitude of another.
Typically, the signal being varied is a contin-
uous sine wave, modulated by a lower fre-
quency signal.
Amplitude - Voltage magnitude of a wave-
form. Most commonly expressed in volts
peak-to-peak, it is also often stated in rms
(root-mean-square) volts (for sine waves).
Attenuation - A decrease in signal ampli-
tude. Usually expressed in decibels (dB). The
output level control of a function generator
provides variable attenuation. Some genera-
tors also provide larger steps of attenuation
via push buttons.
Burst - See Gated Burst.
CMOS (Complementary Metal-Oxide-
Semiconductor) - An integrated circuit fam-
ily which can operate from any supply volt-
age between 3V and 12V (up to 18V in some
varieties), and has low and high supply volt-
age, respectively.
DC Offset - Settable DC voltage superim-
posed with signal output. Used to match the
DC voltage at point of signal injection or for
other special applications.
Distortion (Sine Wave) - A measurement of
waveform irregularities that are introduced to
an otherwise pure waveform. Function gener-
ators typically have less than 0.5% distortion
at frequencies up to 100 kHz.
Duty Cycle - Percentage of cycle during
which the waveform is working (usually the
more positive portion of a square wave or
pulse waveform). Pulse width period divided
by pulse repetition period. The duty cycle of
a perfect square wave is 50%. The duty cycle
of a waveform with a pulse width of 10 ms
and a pulse repetition period of 100 ms is
10%.
FM (Frequency Modulation) - The process
of varying the frequency of one signal in
accordance with the amplitude of another.
Typically, the signal being varied is a contin-
uous sine wave, modulated by a lower fre-
quency signal. The modulated signal general-
ly varies around some mean frequency; the
amount of variation is known as the devia-
tion.
Fall Time - A measurement of how long it
takes a square wave to descend from 90% to
10% of its trailing edge height.
Function - A relationship between voltage
and time, typically periodic, such that for any
specific instant in time, the value of the volt-
age can be determined. Common functions
are sine, triangle and square waves, pulse
trains and ramps.
Gate -Acontrol voltage, typically TTLlevel,
used to turn the output of a function genera-
tor on and off.
Gated Burst (Tone Burst) - A signal being
gated (turned on and off) by another signal. It
is so named because the resulting output is
usually a burst of many cycles followed by an
“off” period of arbitrary duration. However, a
“burst” may consist of as few as one or two
cycles. Although the term “tone burst” is
sometimes used, the frequency of the gated
signal need not be limited to the audio range.
Haversine - A sine wave offset such that its
negative peak rides on the zero-volt base line.
Linear - Term used to describe one type of
sweep generator operation, in which the rate
of frequency change is constant throughout
the sweep.
Linearity (Triangle Wave) -A measurement
of the slope “straightness” of a triangle wave-
form. Measured as a percentage where 100%
is perfect.
Logarithmic - Term used to describe one
type of sweep generator operation, in which
the time period for each “decade” of frequen-
cy change (i.e. 20 Hz to 200 Hz, 200 Hz to 2
kHz, etc.) is equal. This produces a slow rate
of frequency change at the low end of the
sweep, changing to a much faster rate at the
high end.
Offset - See DC Offset
Peak-to-Peak - A method of expressing the
amplitude of a sine, triangle or square wave.
The peak-to-peak voltage represents the volt-
age difference between the maximum and
minimum value of the waveform.
Periodic - Occurring in repeated cycles or
periods.
Pulse Repetition Period -Time between two
successive leading ( or trailing) edges of a
pulse train, usually expressed in microsec-
onds or milliseconds.
Pulse Repetition Rate- Frequency of a pulse
train, usually expressed in pulses per second
or in hertz.
Pulse Width - Period of time (usually mea-
sured in µs) that pulse is active.
Ramp Waveform - A triangle wave whose
excursions between minimum and maximum
have been altered so as to be unequal in
length. For example, the positive-to-negative
portion may constitute 70% of the period,
while the negative-to-positive cycle uses
30%. Such variation corresponds to adjust-
ment of symmetry in a square wave. A ramp
with one transition almost vertical is com-
monly called a sawtooth.
Rise Time - A measurement of how long it
takes a square wave to ascend from 10% to
90% of its rising edge height.
RMS (root-mean-square) - A method of
expressing the amplitude of a periodic wave-
form, most commonly used with sine waves.
The rms voltage of a periodic waveform is
the value of a DC voltage which would deliv-
er the same effective power to a load as does
the periodic waveform.
Sawtooth - A ramp waveform in which one
of the transitions between minimum and
maximum, either positive- or negative -
going, is nearly vertical.
Sine Wave - A waveform, available on most
function generators, which fulfills the equa-
tion y = sin t, where y is output voltage and t
is time. The waveshape varies gradually and
periodically between a minimum and maxi-
mum value, with steep slope at the zero-
crossings and zero slope at the peaks.
Slewed Sine -A sine wave whose excursions
between minimum and maximum have been
altered so as to be unequal in length. For
example, the positive-to-negative portion
may constitute 70% of the period, while the
negative-to-positive cycle uses 30%. Such
variation corresponds to adjustment of sym-
metry in a square wave.
Square Wave - A periodic waveform that
alternately assumes one of two fixed values,
usually for equal lengths of time. When these
times are not equal, the waveform becomes a
pulse (train). The transition times (rise/fall
times) are negligible by comparison.
S t a b i l i t y - Amount of amplitude change
(amplitude stability) or frequency change
(frequency stability) over a specified period
of time after unit is thoroughly warmed up.
2
COMMON FUNCTION GENERATOR TERMS
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