Tektronix TDS 684A, TDS 744A, TDS 784A - page 77

Acquiring and Displaying Waveforms
3–22 TDS 684A, TDS 744A, & TDS 784A User Manual
Peak Detect Mode. TDS 700A models only: Peak Detect mode alternates between
saving the highest sample in one acquisition interval and lowest sample in the
next acquisition interval. Peak Detect mode only works with real-time, noninter-
polated sampling.
If you set the time base so fast that it requires real-time interpolation or
equivalent-time sampling, the mode automatically changes from Peak Detect to
Sample, although the menu selection will not change.
Hi Res Mode. TDS 700A models only: Hi Res mode averages all samples taken
during an acquisition interval to create a record point. The average results in a
higher-resolution, lower-bandwidth waveform.
A key advantage of Hi Res is its potential for increasing resolution regardless of
the input signal. Table 3–3 and the equations shown below illustrate how you
can obtain up to 15 significant bits with Hi res mode. Note that the resolution
improvements are limited to speeds slower than 100 ns/div. Also, resolutions
above 15 bits are not allowed by internal hardware and computation limitations.
Si = Sampling Interval for TDS 744A = 1 ns
t = Sample Interval = Time Div
Number Of Points/Div = 5 msDiv 50 PointsDiv = 100 ns
Nd = Number of points per decimation interval = Dt
Si = 100
Resolution Enhancement (bits) = 0.5 LOG2(Nd) 3 extra bits
Bits of Resolution = Resolution Enhancement (3 bits) + 8 bits 11 bits
Hi Res mode only works with real-time, noninterpolated sampling. If you set the
time base so fast that it requires real-time interpolation or equivalent-time
sampling, the mode automatically becomes Sample even though the menu
selection will not change.
Table 3–3: Additional Resolution Bits
Time Base Speed Bits of Resolution
100 ns and faster 8 bits
200 ns to 500 ns 9 bits
1 s to 2 s10 bits
5 s to 10 s11 bits
20 s to 50 s12 bits
100 s to 200 s13 bits
500 s 14 bits
1 ms and slower 15 bits