Tektronix CSA8000B Series, User Manual

Page: 105 / 354

Acquiring Waveforms
CSA8000B & TDS8000B User Manual
3- 31
The instrument must be in Average or Sample acquisition modes; FrameScan
excludes Envelope acquisition mode.
The key points that follow describe FrameScan mode operating behavior and
provide background to help you to use this feature.
Determine Start Bit and Scan Bits. You need to know the bit in the bit stream at
which you want to start the scan, the appropriate horizontal scale, the starting
horizontal position, and the total number of bits for the desired FrameScan cycle.
How FrameScan Mode Acquires.
FrameScan mode alters the normal acquisition
sequence in order to scan a pseudo-random bit sequence (PRBS) or another
repetitive bit stream to acquire one bit at time in the same sequence found in the
bit stream:
H
Triggering is synchronous with the bit streams (framing signal) of the
communication signal you want to scan, which results in the acquisition of a
single sample prior the scanning of the next bit. You must supply an external
trigger source that is synchronous with the frame; possible sources are
external frame trigger/sync signals from a pattern generator or from a BERT
(Bit Error Rate Tester).
H
Acquisition operates in a scanning mode, where:
a. horizontal position is set to acquire the first bit, which the acquisition
system acquires as a subframe (see Figure 3--10 on page 3--32).
b. horizontal position is incremented one-bit period (1/bit rate), and then
the acquisition system acquires the second bit as a subframe. The
duration of each subframe acquisition is set to provide about a 20%
overlap between frames.
c. This sequence of incrementing, and then acquiring the next bit,
continues until the instrument acquires the number of bits you specify
What’s Excluded?
Keys to Using