Datasheet
SNAU118
LMK01801BEVAL Evaluation Board Operating Instructions
41
Appendix G: Differential Voltage Measurement Terminology
The differential voltage of a differential signal can be described by two different definitions
causing confusion when reading datasheets or communicating with other engineers. This section
will address the measurement and description of a differential signal so that the reader will be
able to understand and discern between the two different definitions when used.
The first definition used to describe a differential signal is the absolute value of the voltage
potential between the inverting and non-inverting signal. The symbol for this first measurement
is typically V
ID
or V
OD
depending on if an input or output voltage is being described.
The second definition used to describe a differential signal is to measure the potential of the non-
inverting signal with respect to the inverting signal. The symbol for this second measurement is
V
SS
and is a calculated parameter. Nowhere in the IC does this signal exist with respect to
ground, it only exists in reference to its differential pair. V
SS
can be measured directly by
oscilloscopes with floating references; otherwise this value can be calculated as twice the value
of V
OD
as described in the first section
Figure 24 illustrates the two different definitions side-by-side for inputs and Figure 25 illustrates
the two different definitions side-by-side for outputs. The V
ID
and V
OD
definitions show V
A
and
V
B
DC levels that the non-inverting and inverting signals toggle between with respect to ground.
V
SS
input and output definitions show that if the inverting signal is considered the voltage
potential reference, the non-inverting signal voltage potential is now increasing and decreasing
above and below the non-inverting reference. Thus the peak-to-peak voltage of the differential
signal can be measured.
V
ID
and V
OD
are often defined in volts (V) and V
SS
is often defined as volts peak-to-peak (V
PP
).
Figure 24 - Two Different Definitions
for Differential Output Signals
Figure 25 - Two Different Definitions
for Differential Input Signals