2-14
Functional Description
The minimum number of pre-trigger samples is 1; the maximum number
of pre-trigger samples is 8,192.
Notes:
The term pre-trigger acquisition is often used for an about-trigger
acquisition when only the samples before the trigger event are significant.
The DAS-4300 Series Function Call Driver differentiates between
pre-trigger acquisition (where the number of post-trigger samples is zero)
and about-trigger acquisition (where you specify the number of
post-trigger samples); refer to the
DAS-4300 Series Function Call Driver
User’s Guide
for information. The DAS-4300 scope and test program
uses the term pre-trigger mode for both pre-trigger acquisition and
about-trigger acquisition.
You cannot specify a post-trigger delay for an about-trigger acquisition.
VTX does not support about-trigger acquisition.
Equivalent Time Sampling (ETS)
Equivalent time sampling (ETS) is an advanced feature that allows you to
digitize high-frequency analog input signals and achieve faster conversion
rates than 1 Gsamples/s. The advantage of ETS is that the total number of
acquisitions needed to collect a waveform is deterministic; therefore, ETS
is ideal for scanning repetitive waveforms quickly.
On the DAS-4301/8K board, ETS is implemented through a patented
circuit (U.S. Patent No. 4,595,908). The analog signal to be digitized
must be repetitive and coherent with a TTL-level trigger out signal on the
Trg IO connector of the DAS-4301/8K board.
Using ETS, the board samples a repetitive signal several times with the
pacer clock shifted relative to the input signal by a fraction of the sample
period. With N acquisitions and a pacer clock shifted by the fraction of
the sample period 1/(N * f
clock
) between the acquisitions, the effective
conversion rate is N * f
clock
. N is called the ETS factor. The maximum
ETS factor is 20, corresponding to an effective conversion rate of
20 Gsamples/second. Other supported ETS factors are as follows: 2, 4, 5,
Summary of Contents for DAS-4300 Series
Page 1: ...DAS 4300 Series U S E R S G U I D E...
Page 2: ...DAS 4300 Series User s Guide Revision A June 1995 Part Number 94520...
Page 21: ...2 6 Functional Description Figure 2 2 Host Computer Memory Address Space...
Page 90: ...C 9 Figure C 16 0 125 V Input Range Gain Code 15 0 125 V Input Range Gain Code 15...