Probing Techniques and Tradeoffs (Part VIII): Gain/Attenuation vs. Noise

Figure 1: Noise comparison of a
Teledyne LeCroy D1605 probe and
a competing model

When discussing oscilloscope probes and dynamic range as we've been doing of late, we must also touch upon the associated topics of internal gain/attenuation and how that relates to noise.

Probing Techniques and Tradeoffs (Part VII): More on Dynamic Range

Figure 1: Input offset range is how much
differential offset a probe can apply to
an input signal to bring it within its
differential-mode output range

In our last post in this series, we'd begun discussing the third of three types of dynamic range as applied to probes, and that is input offset range. This is the maximum differential offset that a probe can apply to the input signal to bring it within the probe's differential-mode dynamic range.

Testing Techniques For Switch-Mode Power Supplies

Figure 1: A simplified schematic of
a switch-mode power supply circuit

On its journey from wall socket to the device being powered, power typically passes through a switch-mode power supply, where the AC signal is rectified into DC before it reaches the device. After that, the DC signal (often 5 V) is passed on to DC-DC converters on the device's PC board for feeding various voltages to branches of the device's power-delivery network. Let's look at some of the measurement techniques and considerations relative to testing switch-mode power supplies.

Back to Basics: Probes (Part IV)

Figure 1: An example of
differential probes
measuring from test
point to test point.

In three earlier posts on the basics of oscilloscope probes, we've taken a broad overview approach, looked more deeply at passive probes and inductance effects, and most recently, dug into active probes. Next up is differential probes, a different animal entirely from the foregoing types.

Back to Basics: Differential Probing

Figure 1: Emitter voltage measurement
in simplified schematic view

Whether or not we think of it in such terms, any voltage measurement taken with an oscilloscope or voltmeter is, in reality, a differential voltage measurement. A voltage is, by definition, the difference in electrical potential between two points in a circuit. It's impossible to take a voltage measurement with only one voltmeter lead. One lead must be attached to the point of interest while the other must be connected somewhere else as a reference point.