03 | Keysight | N5461A Serial Data Equalization Software for Infiniium Series Oscilloscopes - Data Sheet

Equalization FAQ

1. Why do I need equalization?

As data rates go up, the signal deteriorates from the transmitter to the receiver

due to ISI, noise, etc. The more loss that occurs, the more difficult it is for a

receiver comparator to distinguish a “1” from a “0”. A high data rate coupled

with a lossy channel will cause an open eye at a transmitter to be closed at the

receiver. Receivers need to be able to evaluate 1s and 0s. As eyes get more and

more closed, the receiver has a more difficult time interpreting the correct value

as a 1 or a 0. This difficulty ultimately leads to significant data corruption and

errors. Equalization uses advanced filtering techniques to correct the voltage

level of the current bit. By removing much of the intersymbol interference through

filtering, equalization can improve closed eyes into open eyes and significantly

reduce the data corruption. The equalization software provides insight into

designers’ equalizer designs and key data into the viability of the channel link after

equalization.

2. What is the difference between decision feedback equalization (DFE) and feed-

forward equalization (FFE)?

FFE typically looks only at the bits preceding the current bit to open the eye while

DFE dynamically will change based on the current bit in addition to any previous

bits. FFE uses the same filter for each receiver and every bit. DFE is adaptive and

can vary by device. DFE can be used in addition to FFE; however FFE cannot be

used in addition to DFE.

3. Why is it important to use an oscilloscope with low noise when using equalization

software?

If an oscilloscope has the lowest noise, the equalization technique will open the

eye wider. Keep in mind that equalization will amplify any noise not caused by

ISI, which by definition includes oscilloscope noise. Infiniium oscilloscopes have

the industry’s lowest noise floor, so there is much less noise to be amplified. This

results in greater equalization accuracy.

4. Why does the equalization software require serial data analysis software?

Equalization requires the oscilloscope to know where the clock transitions. Clock

data recovery allows the scope to know where the transition occurs, making

equalization possible. Full clock data recovery can only be found in the serial data

analysis software package.