1. Free-Running Measurements

Free-running measurements are performed over periods down to the sub-microseconds range, e.g., to measure initial drift of a signal generator or oscillator, to plot linearity of a sweep signal ramp, or to measure short-term stability down to microsecond averaging times. In these cases, measurements are performed at user-selected Sample Intervals, and performed as gap-free measurements in the range 50 ns to 1000 s.

Just start the block measurement and view the profile in the graph presentation mode.

2. Repetitive Sampling Profiling

The measurement setup just described will not work when the profiling demands less than 50 ns intervals between samples.

How to do a VCO step response profiling with 50 samples during a time of 1 us.

This measurement scenario means that you need to come to 20 ns between samples (50 points * 20 ns = 1 ms observation time).

You will need a repetitive input step signal, and you have to repeat your measurement 50 times, taking one new sample per cycle. And every new sample should be delayed 20 ns with respect to the previous one.

Profiling can theoretically be done manually, but the best would be to perform this series of measurements with a dedicated program on PC, controlling the Analyzer and collecting data from it remotely.

The following are required to setup a measurement:

A repetitive input signal (e.g., frequency output of VCO). An external SYNC signal (e.g., step voltage input to VCO). Use of start arming delay (20, 40, 60 ns, etc). See Figure 38 for a test setup diagram.

Figure 41. Setup for transient profiling of a VCO.

3. Vrms

When the waveform (e.g. sinusoidal, triangular, square) of the input signal is known, its crest factor, defined as the quotient (QCF) of the peak (Vp) and RMS (Vrms) values, can be used to set the constant K in the mathematical function K*X+L. The display will then show the actual Vrms value of the input signal, assuming that Vpp is the main parameter.

Example: A sine wave has a crest factor of 1.414 (√2), so the constant in the formula above will be 0.354.