Atec Tektronix-1502 - Manual (Page 27)

TM 9-4935-601-14-3&P
Sequential equivalent-time sampling is used to develop a display. Two ramps are generated, a fast ramp
and a slow ramp. The fast ramp is compared to the slow ramp or a fixed reference to generate trigger pulses
for the Sampler and the Pulser respectively. These comparisons are made by the Pulser and Sampler
Comparators.
A short time after the Pulser transmits the step pulse into the cable under test, depending on the
amplitude of the slow and fast ramps, a sampling trigger from the Sampler Comparator causes the Sampler to
sample-and-hold the voltage level appearing at that time. This voltage is taken at the point where the Sampler
is connected to the 50
Ω
strip line. This voltage sample is amplified and sent through the vertical amplifiers to
the crt.
The Slow Ramp Generator provides the horizontal sweep for the crt and, combined with the vertical
sample, provides a display of the sampled value. Sampling triggers, taken later during the next fast ramp time,
cause additional samples to be displayed next to the first one, until a line of very short dashes are formed
across the crt, appearing as a solid line (Fig. 3-2).
The amplified vertical and ramp signals are also sent to X-Y Interface connectors. These signals, along
with a pen lift control signal, provide the information for driving external X-Y recorders.
If the TEKTRONIX Y-T Chart Recorder is used, the amplified vertical signals from the Sampler are
applied to the writing stylus drive circuits. The speed of the chart paper is derived by the holes along the edge
of the chart paper passing between a phototransistor and a light-emitting diode providing digital information to
the Control Logic. The Control Logic uses this information to control the slope of the slow ramp so as to match
the speed of the chart paper. Thus, the trace and grid on the chart recording correlates to the trace and
graticule displayed on the crt.
When the horizontal scan of the crt has been completed, the vertical input is automatically disconnected
and the slow ramp is released to scan at its own speed. The chart paper continues to run until the entire
recorded data is outside the chart recorder.
Figure 3-2. Sampling Diagram.
REV A FEB 1980
3-2