Logic analyser

Logic analyzers are widely used to develop and debug electronic logic circuits - they display traces of multiple logic channels and reveal the circuit operation.

A logic analyzer is an electronic instrument that captures and displays multiple signals from a digital system or digital circuit. A logic analyzer may convert the captured data into timing diagrams, protocol decodes, state machine traces, assembly language, or may correlate assembly with source-level software. Logic analyzers have advanced triggering capabilities, and are useful when a user needs to see the timing relationships between many signals in a digital system.

Logic analyser types

Although development of these test instruments is on-going and new variants are constantly being launched and many technology innovations are being achieved, there are some main categories into which most logic analyzers can be split:

Modular logic analyzers

This type of logic analyser is probably what may be thought of as the most typical form of test instrument, although it is the highest cost option providing the highest level of functionality. It comprises a chassis and the various modules - including channel modules. The number of modules being larger for the higher channel counts.

Portable logic analyzers

In a number of instances there may be a need for a smaller analyser, possibly for restricted budgets or for field service. These test instruments incorporate all elements of the analyser into a single box for ease of transportation.

PC based logic analyzers

There is a growing number of PC based logic analysers. These consist of an analyser unit that is connected to a PC. USB is an obvious option for this, but Ethernet is also widely used because of its high speed. This form of PC based instrument uses the processing power of the PC combined with its display to reduce the cost of the overall system. For the future it is likely that PC based logic analyzers and in particular USB logic analyzers will be used increasingly, especially as the cost of USB analyzers can be much lower than other forms, and they can offer high levels of performance using the power of the associated computer.

What is a Logic Analyzer

Logic analyzers are test instruments that are widely used for testing complex digital or logic circuits. They meet the need for users who need to be able to investigate and understand the operation of these circuits.

Oscilloscopes can perform many of the functions of a logic analyser but the the logic analyzer is able to display relative timing of a large number of signals. Essentially a logic analyser enables traces of logic signals to be seen in such a way that the operation of several lines in a digital circuit can be monitored and investigated.

However many oscilloscopes are now able to incorporate many logic analyzer functions in what may be termed a mixed signal oscilloscope.

Logic analysers come in a variety of formats. Although it is possible to obtain those that use a traditional test equipment case, many more are now linked to computers and in this way have much greater levels of flexibility and processing power.

Logic analyser development

The first logic analysers were developed out of the need to be able de-bug and undertake fault-finding on microprocessor based systems.

In the early 1980s when these chips first started to become widely used, the urgent need arose to develop techniques that would enable the many lines and test points to be monitored simultaneously. Existing oscilloscopes were not able to provide the required levels of functionality.

After the early introduction of the first analysers, their complexity increased in line with the complexity of the circuits being tested. The number of channels grew, their speeds rose and the functionality in areas such as triggering improved greatly.

Logic analyser characteristics

There are several key characteristics of a logic analyser that separate it from multi-channel oscilloscopes and other test instruments

Multiple channels

Logic analyzers are designed to monitor a large number of digital lines. As logic analyzers are optimised for monitoring a large number of digital circuits, typically they may have anywhere between about 32 and 200+ channels they can monitor, each channel monitoring one digital line. However some specialised logic analyzers are suitably scaled to be able to handle many more lines, and in this way enable tracking and fault finding on much more complex systems.

Provide a time display of logic states

Logic analysers possess a horizontal time axis and a vertical axis to indicate a logic high or low states. In this way a picture of the digital lines can be easily displayed.

Displays logic states

The vertical display on the analyser displays the logic state as a high of low state. The signals enter the various channels and are converted into a high or low state for further processing within the analyser. It provides a logic timing diagram of the various lines being monitored.

Does NOT display analogue information

These test instruments do not present any analogue information, and in this way they differ from an oscilloscope. They are purely aimed at monitoring the logic operation of the system. If any analogue information is required, then an oscilloscope must be used in addition.

Logic analyser applications

Correlate a large number of digital signals
Investigate the system operation.
Detect timing violations
Trace embedded software operation.

What is a Logic Analyzer, Types and Applications