Logic analyzer

A HP 1615A Logic Analyzer (from 1980)showing a timing diagram.

A Agilent 16801A Logic Analyzer (from 2006)showing a timing diagram with imported scope signals.

A logic analyzer displays signals in a digital circuit that are too fast to be observed by a human being and presents it to a user so that the user can more easily check correct operation of the digital system. Logic analyzers are typically used for capturing data in systems that have too many channels to be examined with an oscilloscope. SW running on the logic analyzer can convert the captured data into timing diagrams, protocol decodes, state machine traces, assembly, or correlate assembly with sourch-level software.

Current analyzers are either mainframes, which consist of a chassis containing the display, controls, control computer, and multiple slots into which the actual data capturing hardware is installed, or standalone units which integrate everything into a single package, with options installed at the factory. Recent mainframe models include the Agilent 16900 and Tek TLA7000, and recent standalone models include the Agilent 16800-series and Tek TLA5000.

Agilent and Tektronix make up over 95% of the industry's revenue.

Operation

A logic analyzer can trigger on a complicated sequence of digital events, and then capture a large amount of digital data from the system under test (SUT). The best logic analyzers behave like software debuggers by showing the flow of the computer program and decoding protocols to show messages and violations.

When logic analyzers first came into use, it was common to attach several hundred "clips" to a digital system. Later, specialized connectors came into use. The evolution of logic analyzer probes has led to a common footprint that multiple vendors support, which provides added freedom to end users. Since 2004, connectorless technology, known as Soft Touch, has become popular. These probes provide a durable, reliable mechanical and electrical connection between the probe and the circuit board with less than 0.7 pF loading per signal.

Once the probes are connected, the user programs the analyzer with the names of each signal, and can group several signals into groups for easier manipulation. Next, a capture mode is chosen, either timing mode, where the input signals are sampled at regular intervals based on an internal or external clock source, or state mode, where one or more of the signals are defined as "clocks," and data is taken on the rising or falling edges of these clocks, optionally using other signals to qualify these clocks.

After the mode is chosen, a trigger condition must be set. A trigger condition can range from simple (such as triggering on a rising or falling edge of a single signal), to the very complex (such as configuring the analyzer to decode the higher levels of the TCP/IP stack and triggering on a certain HTTP packet).

At this point, the user sets the analyzer to "run" mode, either triggering once, or repeatedly triggering.

Once the data is captured, it can be displayed several ways, from the simple (showing waveforms or state listings) to the complex (showing decoded Ethernet protocol traffic). The analyzer can also operate in a "compare" mode, where it compares each captured data set to a previously recorded data set, and stopping triggering when this data set is either matched or not. This is useful for long-term empirical testing. Recent analyzers can even be set to email a copy of the test data to the engineer on a successful trigger.

Uses

Many digital designs, including those of ICs, are simulated to detect defects before the unit is constructed. The simulation usually provides logic analysis displays. Often, complex discrete logic is verified by simulating inputs and testing outputs using boundary scan. Logic analyzers can uncover hardware defects that are not found in simulation. These problems are typically too difficult to model in simulation, or too time consuming to simulate and often cross multiple clock domains.

FPGAs have become a common measurement point for logic analyzers. [1]

See also

* Bus analyzer
* Agilent logic analyzers
* Tektronix logic analyzers