Tektronix CSA7404B, Руководство пользователя

Страница: 271 / 438

Creating and Using Math Waveforms
CSA7000B Series & TDS7000B Series Instruments User Manual
3- 203
H
Tek Exponential Window. The Tek Exponential window (see Figure 3--62)
was invented at Tektronix. In the time domain, it is not a symmetrical bell
shape as is the case with the other windows (see Figure 3--62). Instead, it is
exponential with a peak at the 20% position of the time domain gate. The
frequency domain shape is triangular. Use this window for impulse response
testing where the 20% position is the zero phase reference point. More of the
acquired data record length is used to capture the impulse response. Exact
details of how to compute its values were published in the article, “Impulse--
response testing lets a single test do the work of thousands” by John Pickerd
in
EDN magazine, April 27, 1995, page 95.
1
0
Amplitude
Time
--67 dB side lobe
0
--80
dB
Frequency bins
--40
Figure 3- 62: Tek Exponential window in the time and the frequency domains
Effects of trigger jitter.
The instrument acquisition system has a sample clock that
is asynchronous with respect to the input signal. This means that from one
acquisition to the next, samples may be in a different position on the waveform
with respect to the trigger. Samples may vary in position by up to one sample
interval.