Tektronix TriMode TDP7700 Series Technical Reference page 14

Theory of operation
Figure 4: TDP7700 Series TriMode probe input architecture
6
The TekFlex active probe tip has two inputs, A_IN and B_IN, which can,
depending on the tip design, support TriMode measurements. With a TriMode
tip, such as a TekFlex solder-in tip, it is possible to make differential, single-
ended A, single-ended B, and common-mode measurements, all from a single
soldered differential signal connection to a DUT. The soldered wire connections
between the two probe tip input signal vias and DUT differential signal nodes
should be kept as short as possible (as should the ground via connections if
single-ended measurements will be made). The A and B input signals on the
probe tip pass to a matched pair of damping resistors, Rd, that isolate the probe
connection to the DUT. The damping resistor value of approximately 100 Ω also
serves to tune the probe tip high frequency response. Following each input
damping resistor is a pair of attenuation resistors, Rs and Rp. The attenuation
resistor values depend on the specific probe tip attenuation factor design. There
are currently two attenuation factors available as shown in the following table
with approximate attenuation resistor values. The probe tip attenuation factor in
the table includes an additional 2X factor due to attenuation from the 50 Ω tip
buffer output impedance and the 50 Ω probe amplifier termination impedance.
Table 1: Probe tip attenuation factors
Attenuation Rs
factor
4x 25 kΩ
10x 60 kΩ
Rp Dynamic range
25 kΩ 2.5 V
15 kΩ 6.0 V
TDP7700 Series TriMode Probes Technical Reference
Offset voltage
range
±4.0 V
pp
±10.0 V
pp