Asymmetry Waveform Tester
Original Publication Date: 1992-Jun-01
Included in the Prior Art Database: 2005-Mar-22
A simple waveform measurement system that allows shape comparisons and symmetry measurements using two threshold comparators is disclosed.
Asymmetry Waveform Tester
waveform measurement system that allows shape
comparisons and symmetry measurements using two threshold comparators
method of the invention is the application of two
threshold comparators to the waveform at two different levels. The
output of each comparator has a positive digital level when the
waveform is larger than the reference. This allows some comparisons
of the differences in time from one reference to the other.
Measurements as done with a time interval analyzer normally operate
from one threshold. Even if different measurements are made with the
threshold at different levels, there is no knowledge of the time
difference between the measurements. If the pulse is wider at a
lower amplitude by a given amount, the amount that the two edges
separately contributed cannot be determined. However, with the
disclosed method using two simultaneous threshold comparators,
several different types of relative measurements can be made.
illustrates one type of measurement. The
line AA --- AA
indicates the level of the first threshold, considered to be fixed
for this first example. The rising edge of the first comparator's
output is used to start a timer at the indicated T0 time.
threshold may be moved vertically to different
voltage levels on the waveform. At the top indicated level (dashed
line), the falling level of the comparator output occurs at T1. This
is used to stop the timer, and the result is the difference from T0
to T1. Similarly, as the second reference is successively reduced,
the corresponding times end at T2, T3, T4, T5, or T6, as indicated in
Fig. 1. The result is very similar to triggering an oscilloscope at
T0 on the waveform, and plotting out the waveform. The difference is
that the result comes out as the times versus the voltage level of
the reference, as opposed to voltages versus time in an oscilloscope.
As such, only the portion of the waveform from the positive peak to
the negative peak can be found. If the waveform has a "ring" around
the baseline, a discontinuity will occur. Additional digital
circuits could be added to output either the first, second, or third
(etc.) downward branches of a waveform.
can be done in the reverse order, as illustrated in
Fig. 2. In this case, the first threshold, sensitive to the rising
edge is considered the variable level threshold. The second
comparator used for the falling level, is used as the fixed
reference. In this way, the times from the left side of the waveform
to a fixed trigger point on the right can be determined.
The lower two
dashed lines had starting times on the waveform
off the left side of the graph. This measurement allows the total