Teledyne LeCroy WaveExpert 100H Operators Manual - Manual (Page 192)

Operator’s Manual
190
WE-OM-E Rev A
The opposite may be true if the noise is mostly at lower frequencies. SNR improvement due to the
removal of coherent noise signals -- feed-through of clock signals, for example -- is determined by
the fall of the dominant frequency components of the signal in the passband. This is easily
ascertained using spectral analysis. The filters have a precisely constant zero-phase response.
This has two benefits. First, the filters do not distort the relative position of different events in the
waveform, even if the events' frequency content is different. Second, because the waveforms are
stored, the delay normally associated with filtering (between the input and output waveforms) can
be exactly compensated during the computation of the filtered waveform.
The filters have been given exact unity gain at low frequency. Enhanced resolution should therefore
not cause overflow if the source data is not overflowed. If part of the source trace were to overflow,
filtering would be allowed, but the results in the vicinity of the overflowed data -- the filter impulse
response length -- would be incorrect. This is because in some circumstances an overflow may be
a spike of only one or two samples, and the energy in this spike may not be enough to significantly
affect the results. It would then be undesirable to disallow the whole trace.
The following examples illustrate how you might use the instrument's enhanced resolution function.
In low-pass filtering: The spectrum of a square
signal before (left top) and after (left bottom)
enhanced resolution processing. The result
clearly illustrates how the filter rejects
high-frequency components from the signal. The
higher the bit enhancement, the lower the
resulting bandwidth.
To increase vertical resolution: In the example
at left, the lower ("inner") trace has been
significantly enhanced by a three-bit enhanced
resolution function.