N1076A Datasheet, PDF (3/19 Pages) Keysight Technologies – Electrical and Optical Clock Data Recovery Solutions

03 | Keysight | Electrical and Optical Clock Data Recovery Solutions - Data Sheet
What Does Clock Recovery Do?
The N1076A/77A clock recovery takes an incoming data (or clock) signal, locks onto it using
a phase-locked loop (PLL) circuit, and outputs a recovered clock. The recovered clock can be
used as a timing reference for oscilloscopes or BERTs.
Device Under
Test (DUT)
Clock recovery
Data
Input
Phase
detector
Narrow CR loop BW
Phase
error
amp
Phase Locked Loop (PLL)
Voltage
controlled
Oscillator
(VC0)
Recovered clock
Wide CR loop BW
Timing reference
(Excample: Clock
for Oscilloscope
or BERT)
PLL response is frequency dependent
Peaking
JTF
OJTF
3 dB BW
Frequency
Figure 2. Clock recovery can be used to extract a timing reference signal from an incoming data signal. The
amount of jitter on the recovered clock is determined by the loop bandwidth of the PLL.
Standards typically specify loop order, bandwidth, and peaking, all of which determines how
much jitter on the incoming signal will appear on the recovered clock (also known as the jitter
transfer function, or JTF). Users can configure the FlexDCA graphical user interface (GUI) to
adjust these parameters and ensure standards-compliant clock recovery (often referred to as a
“golden PLL”).
Why Use Clock Recovery?
Standards compliance
To comply with standards such as IEEE 802.3 Ethernet, Fibre Channel, or the Optical
Interworking Forum – Common Electrical Interface (OIF-CEI), clock recovery must be used
when performing measurements such as jitter, eye width, and/or eye height.
Clock-less devices
Another reason to use clock recovery is when a clock or trigger signal is not provided by the
device under test (DUT), but a clock is required to trigger an oscilloscope, or the error detector
in a BERT.
Device under
test (DUT)
Signal In
Oscilloscope
Clock recovery
(CRU)
Trigger In
Figure 3. Clock recovery provides a compliant trigger signal for use by an oscilloscope or BERT.