HP 8753E manual PgBlQ6-c

pgBlQ6-c

Figure 6-68.

Time Domain Low Pass Measurement of an Amplifier Small Signal

Transient Response

Interpreting the low pass step transmission response horizontal axis. The low pass transmission measurement horizontal axis displays the average transit time through the test device over the frequency range used in the measurement. The response of the thru connection used in the calibration is a step that reaches 50% unit height at approximately time = 0. The rise time is determined by the highest frequency used in the frequency domain measurement. The step is a unit high step, which indicates no loss for the thru calibration. When a device is inserted, the time axis indicates the propagation delay or electrical length of the device. The markers read the electrical delay in both time and distance. The distance can be scaled by an appropriate velocity factor as described earlier in this section under “Time domain bandpass. n

Interpreting the low pass step transmission response vertical axis. In the real format, the vertical azis displays the transmission response in real units (for example, volts). For the amplifier example in Figure 6-68, if the amplifier input is a step of 1 volt, the output,

2.4 nanoseconds after the step (indicated by marker l), is 5.84 volts.

In the log magnitude format, the ampliher gain is the steady state value displayed after the initial transients die out.

Measuring separate transmission paths through the test device using low pass impulse mode. The low pass impulse mode can be used to identify different transmission paths through a test device that has a response at frequencies down to dc (or at least has a predictable response, above the noise floor, below 30 kHz). For example, use the low pass impulse mode to measure the relative transmission times through a multi-path device such as a power divider. Another example is to measure the pulse dispersion through a broadband transmission line, such as a fiber optic cable. Both examples are illustrated in F’igure 6-69. The horizontal and vertical axes can be interpreted as already described in this section under “Time Domain Bandpass”,

6-134 Application and Operation Concepts