Clock Recovery
If an external trigger signal is not available, you can use a clock recovery module to derive a trigger signal from the input data signal. This can be either a recovered clock or data trigger. Clock triggers are produced through a clock recovery process. The trigger is routed directly into the oscilloscope on N1060A, 83108A/B, 83496A/B, and 83491/2/3/4A modules. Using clock recovery generally involves selecting the trigger source, symbol rate, and, if available, loop bandwidth through the Setup dialog. Click Setup > Modules > Clock Recovery. Clock recovery modules (excluding the 83495A) can also perform the task of regenerating data. As with the recovered clock, the regenerated data is available at the module's front panel. This allows the module to serve as a multi-rate reference receiver as well as generating trigger signals for waveform measurements.
Clock Recovery Modules
The light emitted from the N1077A, N1078A, 83496A/B, 8349x-series modules with optical Data Out connectors is the slightly attenuated light that is input to the front-panel Data In connectors.
The following table describes the output port for each type of module.
| Module | Output Port | Clock Output |
|---|---|---|
| N1060A Precision Waveform Analyzer |
Recovered Clk Output | Output rate divide ratio is user selectable from 1 to 16 |
| N1078A Optical/Electrical Clock Recovery |
Recovered Clock Out | 125 MHz to 32 GHz (Option 264). 53 GBd to 58 GBd and subrates (Option 253) 125 MHz to 32 GHz (Option 232) 25 GHz to 29 GHz and subrates (Option 225) 125 MHz to 16 GHz (Option 216) |
| N1077A Optical/Electrical Clock Recovery |
Recovered Clock Out | 50 MHz to 16 GHz. |
| N1076B Electrical Clock Recovery |
Recovered Clock Out | 125 MHz to 16 GHz (Option 216). 125 MHz to 32 GHz (Options 232 and 264) |
| N1076A Electrical Clock Recovery |
Recovered Clock Out | 50 MHz to 16 GHz. |
| 86108B Precision Waveform Analyzer |
Recovered Clk Output | Output rate divide ratio is user selectable from 1 to 16 |
| 86108A Precision Waveform Analyzer |
Recovered Clk Output | Full rate output for symbol rates ≤7.1 GBd. Half rate output for symbol rates > 7.1 GBd |
| 83491/2/3/4A Clock Recovery |
Clock | Full rate output. Selected symbol rate must be below 3.2 GBd. |
| 83495A Clock Recovery |
Recovered Clock Out | Output rate is too high for 86100D-STR front-panel Trigger input. |
| 83496A/B Clock Recovery |
Recovered Clock Output | Output rate divide ratio is user selectable from 1 to 16 (≤ 7.1 GBd) and 2 to 16 (7.1 to 13.5 GBd). In clock recovery setup, ensure that divide ratio results in output rate below 3.2 GBd. |
The clock recovery module's input circuits can be damaged by electrostatic discharge (ESD). Therefore, avoid applying static discharges to any front- or rear-panel electrical connector. Before connecting any coaxial cable to the connectors, momentarily short the center and outer conductors of the cable together. Avoid touching the front-panel input connectors without first touching the frame of the instrument. Be sure that the instrument is properly earth-grounded to prevent buildup of static charge.
Fiber-optic connectors are easily damaged when connected to dirty or damaged cables and accessories. When you use improper cleaning and handling techniques, you risk expensive instrument repairs, damaged cables, and compromised measurements.
Because jitter is measured relative to the clock, jitter that is present on both the data and the recovered clock can not be detected by the instrument. Jitter that is within the clock recovery module's loop bandwidth appears on the recovered clock. Jitter that is outside of the loop bandwidth does not appear on the recovered clock and can be detected on the data.