Tektronix, Inc.

Henry G Fox

Douglas C Stevens

Gordon W Shank

Kevin A Robertson

An apparatus and method for digitizing a repetitive waveform using an analog oscilloscope uses a successive approximation technique. For each sample point on the repetitive waveform a digitizing level is compared with the repetitive waveform at that sample point, and the digitizing level is adjusted until it essentially equals the magnitude of the repetitive waveform at that point. The particular sample point is determined by comparing a delay level with a ramp signal that starts from an initial fixed trigger point on the repetitive waveform. Each point is digitized in this manner in one of three modes. The first mode samples the same point on successive iterations of the waveform until that point is digitized, and then the next point is digitized. The second mode samples each point once per iteration of the waveform by stepping the delay level n times during each iteration, and adjusting the digitizing level individually for each sample point until the digitization is complete. The third mode generates a fast ramp having n cycles per iteration of the waveform so that the delay level stays the same, but each sample point is sampled once each waveform iteration. Otherwise it is essentially the same as mode two. In like manner maxima and minima for segments of the waveform may be determined using a window interval rather than a sample pulse.

Analog oscilloscope digitizer

An automatic period and frequency measurement feature for an analog oscilloscope uses a single sweep signal and a delay trigger to detect edges. The sweep rate for the sweep signal is set to the highest rate that provides at least one cycle of the input signal on a display. By varying a programmable level that is compared with the sweep signal, a first event after the start of the sweep is searched for. Once a first event is located, then a second event is searched for in the same manner, reducing the sweep rate if necessary to provide the second event on the display. From the programmable levels corresponding to the first and second events a period and frequency are computed and displayed.

Automatic period and frequency measurements

A delay time between the start of a trace on an oscilloscope screen and a point along the trace is computed based on measured 'sweep gain' and 'sweep start' parameters characterizing a triggered sweep signal controlling the horizontal position of an electron beam creating the trace, the sweep signal increasing when triggered from a starting level at a constant slew rate to move the beam at a constant speed across the screen. The sweep start parameter is the value of input data applied to a digital-to-analog converter (DAC) which would cause the DAC to produce an output voltage equal to the sweep signal starting level, and the sweep gain indicates the rate of increase in DAC input data required to produce a DAC output signal with a rate of increase similar to the slew rate of the sweep signal. The horizontal position of the point along the trace is the beam position on the screen at the moment the sweep signal magnitude reaches the magnitude of the DAC output signal. The delay time is computed as the difference between the DAC input data resulting in this DAC output signal magnitude and the sweep start parameter, the difference being divided by the sweep gain parameter.

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Sherwood, OR, United States of America

Henry G Fox