Operators Manual Owner manual

Operator's Manual

The improvement in SNR corresponds to the improvement in resolution if the noise in the signal is white

(evenly distributed across the frequency spectrum).

If the noise power is biased towards high frequencies, the SNR improvement will be better than the

resolution improvement.

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.

Example ERes Applications

The following examples illustrate how you might use the instrument's enhanced resolution function.

Graph 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.

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