Teledyne LeCroy WaveExpert 100H Operators Manual - Manual (Page 17)

Wave Expert
WE-OM-E Rev A
15
INTRODUCTION
Wave Expert 100H is an equivalent time sampling oscilloscope system consisting of a mainframe
and up to four plug-in acquisition pods or modules. Different modules allow the connection of either
optical or electrical signals to the instrument and bandwidths up to 100 GHz are available. In
addition to the acquisition modules, PPG (pulse pattern generator) and CDR (clock and data
recovery) modules are also available.
The heart of Wave Expert is the timebase which is housed in the mainframe. The timebase controls
the acquisition heads by supplying a sampling pulse or strobe to the modules and digitizers which
convert the stored charge in the modules into a numerical voltage value for display. Unlike more
common DSO’s, the timebase in Wave Expert samples only in the equivalent-time mode, that is, it
samples at a rate much lower than its bandwidth but synchronous to the signal under test. This type
of sampling requires that the signal under test be periodic and the timebase samples the signal at
least once per period. The displayed waveform is built-up from multiple acquisitions of a single
period of the signal with each acquisition being at a progressively longer delay from the previous
one relative to the phase of the signal under test. This acquisition method is known as sequential
sampling. Sequential sampling utilizes a trigger signal to determine the phase of the signal under
test and the sampling strobe is generated by the timebase after a delay from the trigger. One
sample is taken per trigger and the delay is slightly increased on each subsequent trigger. The
sampling rate in this acquisition mode is determined by the trigger rate but is no faster than 500
kS/s.
Wave Expert 100H also features a powerful new sampling technique called High stability Coherent
Interleaved Sampling (HCIS).This optional timebase (WE-HCIS) enables samples to be acquired at
the rate of 10 MS/s independent of the trigger rate. HCIS does this by generating a sampling strobe
that is phase-locked to the clock of the signal under test. An internal phase locked loop generates a
10 MHz strobe that is precisely offset from an integer sub-multiple of the signal clock so that the
sampling point moves relative to the phase of the signal from sample to sample. The signal is
constructed in much the same way as the sequential timebase except that the sampling rate is fixed
at 10 MHz. The HCIS timebase has several distinct advantages over sequential sampling:
• 10 MHz sampling rate independent of the trigger
• very low intrinsic jitter – 230 fs RMS (typical)
• automatic pattern locking up to PRBS23
• long waveform memory up to 510 M samples
The phase locked loop used to derive the sampling strobe from the clock is designed with a very
narrow loop bandwidth in order to provide the lowest possible intrinsic jitter. A benefit of this
arrangement is that jitter on the clock signal used as the HCIS reference will not affect the
performance of the timebase. This is not true for sequential timebases where any jitter on the
trigger signal directly translates into timebase jitter.
HCIS is optimized for acquiring high speed serial data signals and the timebase controls are unique
compared to conventional sequential sampling oscilloscopes. The HCIS timebase is set up in terms
of the data signal being measured. The timebase is first locked to the clock from the signal under