Making Single Ended Measurements Using The P77Brwsr Differential Probe Tip; Temperature Compensation; Active Tip Measurement Configuration - Tektronix TriMode TDP7700 Series Technical Reference

Theory of operation
Making single ended
A TriMode tip provides solder connections for a DUT ground reference for both
the A and B probe inputs making single-ended measurements with a TriMode
measurements using the
probe tip straightforward. Although the differential input mode of the probe is
P77BRWSR differential
normally used to make a differential signal measurement, single-ended
probe tip
measurements can be made using Differential Input mode when the probe input
connections and offset voltage controls are configured properly, This single-
ended configuration process is particularly important to understand when using
the tip, since this variable-spacing Browser tip operates only in Differential Input
mode. Differential Input mode provides a measurement of the difference (A – B)
between the A and B input signals. If the probe tip B input is connected to a DUT
ground, the resulting Differential Input mode measurement (A – 0 V) results in a
display of the single-ended A input signal response.
When making differential signal measurements, the P77BRWSR Offset Voltage
control is normally set to the Common-mode (CM) Tracking mode. With CM
tracking mode active, the A and B input signals are monitored and the Offset A
and Offset B settings are both adjusted to match the DC common-mode voltage
of the A and B input signals [(A + B)/2]. The differential Offset voltage should
be set manually to the center of the signal voltage swing. The common mode
offset should be set to 1/4 of the signal swing. For a +5 V CMOS logic signal; for
example, the differential offset voltage should be set to +2.5 V and the common
mode offset should be set +1.25V. The A signal input voltage should then range
from +5 V to 0 V, which is within the 6 Vp-p dynamic range of the Browser tip
as long as the offset voltage is set near the center of its expected voltage swing.
These offset settings maximize the dynamic range of single ended measurements
for the differential browser.
Temperature The TDP7700 Series probes employ temperature compensation to optimize
measurement accuracy.
compensation
Active tip measurement
In many of the high-frequency signaling standards that the TDP7700 Series
probes are designed for, a 50 Ω termination at the transmitter is in parallel with
configuration
another 50 Ω termination at the end of the transmission line path, effectively
making a 25 Ω signal source impedance. In this application, the solder tip or
browser tip measurement configuration is designed to pick off the transmitted
signal at a location in the signal transmission path.
The input impedance for a solder tip, Z probe, varies with frequency. For a
TekFlex solder tip the DC input resistance is about 50 kΩ and decreases with
frequency above about 10 MHz to about 100 Ω above 10 GHz. Refer to the
graphs later in this document for input impedance information. See page
Impedance graphs on page 36.
TDP7700 Series TriMode Probes Technical Reference 25