Don’t confuse the 1-port PDN probe with a 10 to 1 ratio, passive oscilloscope probe. They have little in common with a 1-port PDN probe other than the improvement of the signal-to-noise ratio achieved by the lack of probe attenuation. The 1-port PDN probe is special in many respects and more complicated than meets the eye. This article serves as an introduction to the 1-port PDN probe but also provides examples of how it can be applied to get high-quality measurements quickly and easily.
BROWSER-CLASS PROBE
Several companies manufacture and distribute high-frequency TDR probes. These probes are typically designed for very high-frequency measurement, typically 10GHz or more. These probes are designed to be used in sophisticated probe stations with microscope-supported tip placement.
1-port PDN probes, such as the Picotest P2100A shown in figure 1, are designed to be handheld browser probes. The handheld browser probe shown is a lower frequency probe, supporting DC to 1.5GHz. There are a few notable characteristics that assure high-quality, precise measurements.
PRECISELY 50ohms
The first characteristic is that the probe characteristic impedance must be precisely 50?. Poor connections between the probe cable and the probe connector or a mismatch between the probe cable and the probe head can result in small parasitic capacitance at the probe tip. This leads to poor frequency response and can add considerable (and erroneous) ringing to the measurement. Since the probe pins are inductive, it is important that the probe not be capacitive in order to assure that while the measurement is bandwidth limited due to the tip inductance, it will not ring.