B–7
Enhanced Resolution
Cautionary Notes
Ø The enhanced resolution function can only improve the resolution of a trace; it cannot
improve the accuracy or linearity of the original quantization by the eight-bit ADC.
Ø The constraint of good temporal response excludes the use of maximally-flat filters.
The pass-band will therefore cause signal attenuation for signals near the cut-off
frequency. The highest frequencies passed may be slightly attenuated. The frequency
response of a typical enhanced resolution filter (the 2-bit enhancement filter) is
illustrated below, indicating the –3 dB cut-off frequency of 5.8% of the Nyquist
frequency.
Ø The filtering must be performed on finite record lengths: data will lost at the start and
end of the waveform, so that the trace becomes slightly shorter after filtering.
Ø The number of samples lost is exactly equal to the length of the impulse response of
the filter used, and thus varies between two and 117 samples. Owing to the
oscilloscope’s very long waveform memories, this loss — just 0.2% of a 50 000 point
trace — is not normally noticed. However, it is possible to demand filtering on a record
so short, there would be no data output, and in this case the scope will not allow
filtering.
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