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What Is a Logic Analyzer?

Geisha A. Legazpi
Geisha A. Legazpi

A logic analyzer is a test and piece of monitoring equipment that receives, or captures, several digital circuit signals then displays, with storage capability, the test digital inputs. For instance, in the two-input AND gate, a simple digital device, all the three sensing points, which include two gate inputs and one output, can be captured by a computer that has sampling and storage capability. When software-intensive digital circuits were not so common, the logic analyzer was able to help technical personnel master the complicated states of purely hardware-wired logic circuits. At some point, building a more complicated digital device based on hard-wired logic was no longer a viable option. Even the best logic analyzers will not equal a software-based digital solution, which can generate the debug dumps that are the equivalent of logic analyzer displays and functionality.

The logic analyzer may have several dozens of input ports that are terminated in various ways. A common termination is a micro-clip that can tap into a leg of an integrated circuit being tested. If a combination of inputs and sequences is supposed to produce a given result, the specific input combinations may be programmed as a trigger that will allow the technical analyst to be notified when a certain combination has occurred. For instance, in a 10-input AND gate, the presence of all “1” in the inputs will have to produce a “1” in the output. The logic analyzer can verify that this condition actually happens and may even be able to provide a scrollable list of states prior to the trigger event.

Scientist with beakers
Scientist with beakers

Some logic analyzers can provide digital as well as analog displays, and this is very useful for testing and troubleshooting digital devices that also have correlated analog signals. For instance, in measuring the performance of certain circuits, the level of an analog test point could serve as the needed trigger event to begin a certain process. Analog and digital analyzer probes are available for interface to a laptop. In the radio frequency testing applications, analog spectrum analyzers use a sampling device that gathers the analog signals for display in real time, while the signal processing, storage, and display function are handled by a computer application. A design change in the analyzer could be a simplified software upgrade as compared to purchasing new hardware modules.

Portable logic analyzers take advantage of the computing power of laptops to simplify most of the functions inside a logic analyzer. For instance, a 24-input digital sampling device may have a universal serial bus (USB) adapter. The USB interface then sends the samples to a computer application for storage, display, and even customized analysis.

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      Scientist with beakers