LMK00308 Datasheet, PDF (11/25 Pages) Texas Instruments – 3-GHz 8-Output Differential Clock Buffer/Level Translator

12.0 Measurement Definitions
12.1 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 description.
Figure 1 illustrates the two different definitions side-by-side for inputs and Figure 2 illustrates the two different definitions side-by-
side for outputs. The V_ID (or V_OD) definition show the DC levels, V_IH and V_OL (or V_OH and V_OL), 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 as volts (V) and V_SS is often defined as volts peak-to-peak (V_PP).
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FIGURE 1. Two Different Definitions for Differential Input Signals
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FIGURE 2. Two Different Definitions for Differential Output Signals
Note 25: Refer to Application Note AN-912 Common Data Transmission Parameters and their Definitions for more information.
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