Transmission Measurements In Time Domain Low Pass - Agilent Technologies 8753ET User Manual

Making Time Domain Measurements
Time Domain Low Pass Mode
Figure 3-14 Low Pass Step Measurements of Common Cable Faults (Real Format)

Transmission Measurements in Time Domain Low Pass

Measuring Small Signal Transient Response Using Low Pass Step
Use the low pass mode to analyze the test device's small signal transient response. The transmission
response of a device to a step input is often measured at lower frequencies, using a function generator (to
provide the step to the test device) and a sampling oscilloscope (to analyze the test device output response).
The low pass step mode extends the frequency range of this type of measurement to the maximum
frequency of the analyzer.
The step input shown in Figure 3-15 is the inverse Fourier transform of the frequency domain response of a
thru measured at calibration. The step rise time is proportional to the highest frequency in the frequency
domain sweep; the higher the frequency, the faster the rise time. The frequency sweep in Figure 3-15 is from
10 MHz to 1 GHz.
Figure 3-15 also illustrates the time domain low pass response of an amplifier under test. The average group
delay over the measurement frequency range is the difference in time between the step and the amplifier
response. This time domain response simulates an oscilloscope measurement of the amplifier's small signal
transient response. Note the ringing in the amplifier response that indicates an under-damped design.
3- 19