Probing Techniques and Tradeoffs (Part III)

Figure 1: Bandwidth is defined as the frequency at which
the ratio of the displayed amplitude to the input amplitude
is -3 dB (or 0.707)

Any discussion of oscilloscopes and/or probes must include the topic of analog bandwidth. Bandwidth is one of a short list of key specifications for a testbench setup. All oscilloscopes and probes come to market with a bandwidth specification, which is defined as:

The frequency at which the ratio of the displayed amplitude to the input amplitude is -3 dB (or 0.707).

This is known as the "-3 dB point," or the half-power point (Figure 1). At this frequency, a sine-wave input signal is attenuated to 70.7% of its true amplitude. Any higher frequencies will likely be distorted on the display, making accurate measurements and calibration impossible.

Probing Techniques and Tradeoffs (Part II)

Figure 1: A snapshot of available probes from
Teledyne LeCroy

Our first post in this series concentrated on connectivity and various means by which one might apply an oscilloscope probe to a circuit or device under test. Now, we'll look at an "ideal" probe vs. a real-world probe, and then begin a discussion of probe specifications.

Probing Techniques and Tradeoffs (Part I)

Figure 1: Probes are the signal's gateway to the oscilloscope

As any oscilloscope user (hopefully) knows, probing is perhaps the most critical element of getting good measurement results (Figure 1). We must understand our probes' specifications to ensure that we obtain the best possible signal fidelity, and thereby accurately characterize our signal under test. In this series of posts, we'll take you through probing tradeoffs and techniques and help you choose the right probe for the task at hand.