How does the 80E04 TDR step generator work?

How does the 80E04 TDR step generator work?

Both channels in the 80E04 TDR/sampling module have a selectable polarity step generator which gives both channels measurement capabilities. You can use the outputs of both generators to perform differential and common-mode TDR measurements.

The step generator circuitry consists, fundamentally, of a polarity-selectable current source and a diode switch. Initially, before the step, the diode switch is biased to conduct current to the output. When the diode switch opens, the step occurs. A DC current source assures that the baseline level stays close to zero volts. Figure 7, a simplified diagram, shows the switch and the current source.