The BERTScope CR Series work seamlessly with BERTScope Analyzers - You can use

the clock recovery instrument with the BERTScope by connecting the USB cable

between the two instruments. The graphing capability can be displayed on the

BERTScope analyzer by using the "To CR analysis" soft key.

Golden PLL

Many test standards require the use of a Golden PLL (Phase Lock Loop).

Control of the BERTScope CR Series variable loop bandwidth allows for

control of the jitter transferred to the recovered clock. When the loop

bandwidth setting is narrow, much of the high-frequency jitter is removed

from the clock signal. The narrowest LBW setting is desirable when a clock

with the lowest possible jitter is required. When the loop bandwidth setting

is wide, jitter is transferred to the recovered clock, emulating a clock signal

similar to the CDR of the receiver under test. Each standard provides an

optimum LBW setting for clock recovery often called the Golden PLL.

Recover Spread Spectrum clocks for testing

to electrical serial bus standards

Spread Spectrum Clocking (SSC) is an increasingly required feature of

serial bus standards. When employed, it can prove difficult to track but its

effect must be included in test. These instruments are able to track SSC

correctly with large frequency excursions up to 5000 ppm, making them

unique amongst clock recovery test solutions. The BERTScope CR series

is the first clock recovery instrument to recover clocks from spread

spectrum clocked signals used in Serial ATA, SAS, PCI Express, and USB

applications.

Spread spectrum clocks exhibit low-frequency (30-33 kHz) modulation, for

example, resulting in 225 UI (Unit Interval) deviation when imposed on a

3 Gb/s data signal. This frequency deviation is tracked accurately by the

clock recovery instrument when the optional 5-piece cable set is used with

the BERTScope CR Series and BERTScope Analyzer. This cable set is

matched to compensate for the 5 ns delay in BERTScope Analyzer with

SSC signals, thus avoiding jitter amplification.

A signal with SSC was measured with the BERTScope CR Series. Outputs

on the rear panel of the instrument provide monitoring points to view the

loop behavior. When viewed on a low-bandwidth, real-time oscilloscope,

the triangular waveform characteristic of SSC is visible in the lower trace.

The upper waveform displays the difference in phase between data input

and clock recovery output.

Clock Recovery Instrument -- BERTScope CR Series

www.tek.com 3