Tektronix P7313SMA, Техническое описание

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Operating Basics
The inverted polarity of the probe ampli fi er output can be veri fi ed by examining the probe Aux Output signal. The main
probe output signal is routed through the TekConnect interface connector and is automatically scaled to show the correct
differential amplitude at the probe input connectors.
Differential Dynamic Range
The V
CM
compensation circuit in the probe attenuator is designed to maximize the dynamic range of the AC component of the
input signal. For most high-speed serial data signals, the AC component of the signal is of most interest for compliance
testing where an eye pattern display of the differential signal is checked for timing jitter and voltage amplitude and
fi delity.
The DC common-mode component of the input signal is present primarily to bias the signal into the operating range of
the receiver and may even be removed in the transmission path with AC coupling. The V
CM
compensation circuit in the
P7313SMA probe is designed to null out the DC common-mode component of the input signal, V
CM
, so that only the
differential mode component of the input signal is passed through to the probe ampli fi er inputs.
The V
CM
compensation circuit allows the dynamic range of the probe to be speci fi ed as a differential peak-to-peak voltage
with a separate DC common-mode range. The differential peak-to-peak voltage speci fi cation is different for the two probe
attenuation settings, but the DC common-mode range is the same for both attenuation settings.
The DC common-mode range of the probe is actually describing the performance of the V
CM
compensation circuit, rather than
the dynamic range of the probe ampli fi er. The dynamic range of the probe has been speci fi ed as a differential peak-to-peak
voltage because that best represents the way in which the signal is typically displayed and speci fi ed for compliance testing.
Single-Ended Measurement Topology
Although the P7313SMA differential probe can be used to make single-ended measurements, it is important to understand the
impact of the termination network on the measured response, particularly on the DC common-mode component of the signal.
Because of the limited dynamic range of the probe ampli fi er, single-ended measurements, which also display the DC
common-mode component of the signal, must be carefully checked for possible overdrive problems. The single-ended
measurement topology can also affect the performance of Auto mode, which will only function properly with a matched
source impedance con
fi guration.
Three possible single-ended measurement topologies will be examined in this section. They differ in the termination used on
the (-) input of the probe when the single-ended signal is connected to the (+) input.
12 P7313SMA Technical Reference