LMK04832PAPSLASHEM datasheet(15/102 Pages) TI

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7.2 Differential Voltage Measurement Terminology

The differential voltage of a differential signal can be described by two different definitions causing confusion

when reading data sheets 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 distinguish 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 noninverting signal. The symbol for this first measurement is typically VID or VOD 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 noninverting

signal with respect to the inverting signal. The symbol for this second measurement is VSS 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. VSS can be measured directly by oscilloscopes with floating references, otherwise this value can

be calculated as twice the value of VOD as described in the first description.

Figure 7-1 shows the two different definitions side-by-side for inputs and Figure 7-2 shows the two different

definitions side-by-side for outputs. The VID and VOD definitions show VA and VB DC levels that the noninverting

and inverting signals toggle between with respect to ground. VSS input and output definitions show that if the

inverting signal is considered the voltage potential reference, the noninverting signal voltage potential is now

increasing and decreasing above and below the noninverting reference. Thus the peak-to-peak voltage of the

differential signal can be measured.

VID and VOD are often defined as volts (V) and VSS is often defined as volts peak-to-peak (VPP).

GND

VID = | VA s 9B |

VSS = 2 × VID

VID Definition

VSS Definition for Input

Noninverting Clock

Inverting Clock

VID

2 × VID

Figure 7-1. Two Different Definitions for Differential Input Signals

GND

VOD = | VA - VB |

VSS = 2·VOD

VOD Definition

VSS Definition for Output

Non-Inverting Clock

Inverting Clock

VOD

2·VOD

Figure 7-2. Two Different Definitions for Differential Output Signals

Refer to application note AN-912 Common Data Transmission Parameters and their Definitions (SNLA036) for

more information.

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LMK04832-SEP

SNAS838A – OCTOBER 2022 – REVISED NOVEMBER 2022

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