Why would you need a differential probe?

The differential probe is an essential tool for anyone working in an electronics laboratory. Once you have one, you will find many uses for it and wonder how you survived without it. For many situations, it improves productivity by speeding up debugging and improving measurement clarity.

There are three main areas where differential probes are invaluable:

1. Working with high speed differential logic signals.

2. Working with switch mode power supplies or high side switches.

3. Having high power and small signals, or logic in the same system.


1. Working with high speed differential logic signals.

If you have ever designed with DDR or SATA you will know differential logic is used. There are many high speed differential logic standards as listed here:

CML or SCL              Current Mode Logic or Source-Coupled Logic

ECL                            Emitter-Coupled Logic

LVECL                       Low Voltage Emitter-Coupled Logic

PECL                          Positive Emitter-Coupled Logic, also called Pseudo Emitter-Coupled Logic

LVPECL                     Low Voltage PECL

HSTL                          High-Speed Transceiver Logic

LVDS                          Low Voltage Differential logic.

The properties of these high speed differential logic standards vary but they all give better signal integrity than a single ended signal, allowing higher speed for a given trace length. For more details on the properties of these standards, go to Logic.

Most high speed transmission technologies also use differential signals for the same reasons eg. Ethernet 10\100\1000BaseT, USB, SATA.

The DeltaSense active differential probe is optimised for high speed differential logic with high impedance and low capacitance to minimise loading of signals. It also features wide bandwidth and low offset. Because of all these properties, DeltaSense will provide reliable measurement of signal integrity and removal of local ground issues.  These features are a must for tracking down reflection and noise coupling, creating eye diagrams, and measuring set-up and hold time.


2.Working with switch mode power supplies or high side switches

The high side switch is often the most critical part of a switch mode power supply. For any design, it is imperative that the drive to the high side switch be sharp, clean and at the right level. Too high a drive may damage the switching element. Too low a drive or slow rise time will cause inefficiency and overheating. The most common reliability problem is caused by overshooting and ringing. Getting a real representation of drive signal at the high side switch is very simple with the DeltaSense active differential probe.  But it is very difficult without DeltaSense, and requires using a Maths function and subtracting signals within the oscilloscope, which will result in noisy signals because of quantisation error. DeltaSense’s wide bandwidth clearly displays all the signals with great precision.


3.Having high power and small signals, or logic in the same system.

When working on designs that transfer high power, it is common to have smaller control signals. Debugging any of the control signals can be problematic as there is often a large difference in ground potential between the oscilloscope and system under test. The difference in ground potential will swamp the signal of interest, confusing any measurements. DeltaSense active differential probe can solve this problem by allowing the user to see the signal with respect to local ground, thus removing any ground difference problems.