TDR Peeling Operator
The TDR peeling is a signal processing math function that removes unwanted effects from multiple reflections during TDR measurements. TDR peeling cannot be used on TDT responses, because the lack of reflections invalidates the algorithm. So, you could use it on an T11 or S11 response but not on a T21 or S21 response.
When a device has two or more impedance discontinuities, reflections from the second discontinuity reflect off the first discontinuity. This complex interaction of secondary reflections from the stimulus pulse compromises the measured impedance profile and decreases measurement performance. TDR peeling compensates for the complicated interaction between discontinuities. TDR peeling analyzes reflected signals at the source and deconvolves the time domain reflections to create an impedance profile of the device being tested.
You can apply TDR peeling to calibrated, TDR responses by applying the TDR peeling math function to the underlying individual responses. For differential and common stimulus, apply the TDR peeling to the differential or common-mode response trace.
What are the limitations of peeling?
- TDR peeling requires a trace record length of 1024 points or less. Use the Acquisition controls to change the trace length.
- TDR peeling does not account for frequency response losses (for example, PC board transmission lines are lossy devices). The sum of the waves that are incident on a node are assumed to be equivalent to those exiting the node.
- TDR peeling assumes a lossless transmission line (resistance of 0). Any actual resistance (which causes loss, even at DC) degrades the accuracy of peeling.
- Instrument performance is reduced, because the peeling algorithm requires a factorial number of calculations (forward and reverse reflections grow overtime). It is not recommended to peel multiple traces simultaneously.
- The initial impedance mismatch is the most accurate; as distance increases from initial impedance mismatch down the transmission line, the impedance accuracy decreases.
If a problem occurs while using the TDR peeling math function, the waveform may no longer be visible on the display. Causes of this effect include noisy traces as well as opens and shorts in the test setup.
The TDR Peeling operator is only available in TDR/TDT mode.
The TDR Peeling operator requires a single-valued waveform, as opposed to an eye diagram. Be sure that your trigger setup results in a single-valued waveform at the input to this operator. This can be acheived using an external pattern trigger or by using pattern lock. If you are using an external pattern trigger, you may ignore this note.
The operator's Display Setup configures the manner in which the resulting waveform is displayed including both vertical and horizontal scaling. Track selection to allows the output waveform to track changes to the scaling of the input waveform. Track is the default setting. In addition, you can turn the waveform's display off or on and select the color of the trace.
Use the Name button to give the displayed waveform a custom identifying name which is show in the Signals area on the display graticule and in the Signals palette. Custom names are very helpful for screen captures or when multiple waveforms are displayed.
The Graph Window is available when multiple waveform content windows are used.
Use the Signal Type's Track selection to allows the waveform type (NRZ or PAM4) to track the input waveform's type. Track is the default setting. If input waveform's type cannot be automatically determined, select Manual to specify the waveform type.