Tektronix WFM8200, Service Manual

Page: 28 / 85

Theory of Operation
Source Level readout
Jitter waveform display 1
Eye Amplitude readout 1
Eye Risetime readout 1
Eye Falltime readout 1
Eye Rise-Fall (difference) readout 1
1
Requires Option PHY.
NOTE.
SD, HD, and 3 Gb/s signals can be used with these features. All instrument
models come standard with SD-SDI and HD-SDI. 3 Gb/s signals require Option
3G be installed.
The hardware to support these features is contained on the EYE/PHY board. The
Audio blocks are not shown in this block diagram but, if installed, still connect as
shown in the Main Block diagram. (See Figure 2-1 on page 2-2.)
Operation Each SDI input signal is applied to a cable equalizer. The selected input signal is
sampled by a wide-band track-and-hold circuit, and then digitized. The selected
input is also applied to a clock recovery circuit. The recovered clock is divided
by 10 for SD (by 20 for HD),
fi ltered to form a sine wave, and then digitized.
Both the SDI input and the recovered clock sine wave are sampled by the same
asynchronous clock, and then both are passed to the main board for processing
by FPGAs. These arrays produce the Eye Display, Jitter Display, Jitter Readout,
and Jitter Thermometer. The Eye Display data is further processed to derive
the Eye Amplitude, Eye Rise Time, and Eye Fall Time measurements, which
are shown in the SDI Status Display.
The selected SDI input signal also drives the Cable Meter circuit, which measures
signal energy at two frequencies. These measurements are read by the CPU on the
Main board, which calculates Cable Loss, Approximate Cable Length, and Source
Level for display in the SDI Status screen.
2–6 WFM8200 and WFM8300 Waveform Monitors Service Manual