Improving Measurement Accuracy; Dsp Correction Filtering - Tektronix TriMode TDP7700 Series Technical Reference

Theory of operation

Improving measurement accuracy

DSP correction filtering

20
TDP7700 Series probes and probe tips use DSP correction filtering to optimize
probe measurement fidelity. High frequency time domain measurement
performance characteristics such as rise time, aberrations, and pulse flatness are
improved by DSP correction filtering. Similarly, frequency domain performance
characteristics such as bandwidth, frequency response flatness, and differential
signal coupling are improved by DSP correction filtering. DSP correction
filtering is performed automatically by the oscilloscope using S-parameter
characterization data downloaded from probe and probe tip storage memories.
This S-parameter data is unique for each probe and probe tip, rather than the
nominal response data that was used in some previous generation probe families.
Distinct S-parameter data sets are stored in probe memory for each probe input
mode and step gain setting combination. Every different input mode and step
gain combination has a slightly different amplifier signal path, which requires
different signal response correction. Since the solder tip buffers do not have
complex mode switching, only one S-parameter data set is stored in the probe tip
storage memory. The high frequency signal performance of the P77BRWSR
browser tip changes slightly as the tip spacing is adjusted. Several S-parameter
data sets are stored in the browser tip memory and automatically switched to the
optimum data set, under control of the browser tip spacing position detection
circuitry.
S-parameter characterization data are measured for each probe and probe tip as
part of the manufacturing test process. TDP7700 Series probe signal performance
is measured using a 3-port VNA measurement configuration with a 2-port
TekFlex connector input and a 1-port TekVPI interface output. Custom test
fixtures have been developed for making VNA port connections to the probe
TekFlex connector input and TekVPI interface output. Test fixtures designed for
connecting to the probe input and output signal ports are de-embedded to remove
interconnect losses and signal path imperfections.
TekFlex probe tip signal performance is measured using a 4-port VNA
measurement configuration with 2-port input and output connections. Because
the TekFlex probe tips do not have standard RF connectors at their inputs or
outputs, the custom test fixtures inject and receive VNA port signals. Custom
calibration standards were developed to support de-embedding these probe tip
manufacturing test fixtures.
TDP7700 Series TriMode Probes Technical Reference