Teledyne LeCroy oscilloscopes have a feature that allows users to qualify measurements made with any of the automatic measurement parameters. In addition to the existing measurement gate, new acceptance qualifiers include range limits and an external waveform gate. This new feature is described graphically in Figure 1.
The existing measure gate is used to select the desired portion of the waveform over which the measurements will be made. After the measurements are made the acceptance qualifiers, either a waveform gate or a range qualifier, are used to select which of the measurements are included in the final readout.
Figure 2 shows an example of a measurement that requires additional qualification. The parameter being measured is the frequency of the waveform on channel 1 (top trace). An expanded view of the waveform in zoom trace Z1 shows that the leading edges of some of the pulses have multiple transitions. The maximum value of the unqualified frequency measurement shown as P1 is 83MHz. The goal is to measure the frequency of the pulse train while ignoring those pulses that have multiple transitions. The 'Accept' tab of the measure dialog box has been set up to accept only those frequency measurements that fall into a range of 0 to 1.5 MHz. The qualified measurement is shown in parameter P2. Note that in this measurement the maximum value is 1.012 MHz. A comparison of the number of values included in each parameter shows that the qualified parameter has rejected five measurements.
Figure 3 shows a range-qualified measurement of an amplitude parameter, peak-to-peak. Note that the range can be set manually or by using the Find Range button on the Accept tab in the measurement setup dialog box.
As in the previous figure, the parameter P1 is unqualified and the parameter P2 is qualified to accept only measurements within the range of 400 mV to 600 mV. Range qualified measurements are very useful in measuring signals in the presence of glitches and other waveform anomalies.
A waveform-gated measurement is shown in Figure 4.
The waveform in trace C2 is used to accept the measurement whenever the waveform is lower the threshold set in the Accept tab of the measurement setup dialog box. In this example the waveform on channel 2 is above the threshold synchronously with the 'runt' pulses. As can be seen in the parameter readout fields, the qualified measurement, P2, reads only the amplitudes of the pulses outside the gating waveform. At the same time the unqualified parameter, P1, shows the value of all the pulses.
Waveform-gated measurements are ideal for measuring signals related to specific events. For example you can measure the values of a signal only when a specific device is enabled, gating with the chip enables line. On a multiplexed signal line or bus you can use waveform gating to separate transmitted and received components by utilizing the read/write gates.
Both range- and waveform-qualified measurements increase the flexibility of Teledyne LeCroy's parameter measurements, giving the user increased control over when and where measurements are taken.