A look at oscilloscopes and logic analyzers

A tool of choice of electronic engineers, digital oscilloscope has become an indispensable tool in virtually every engineering lab with designers confident and trusting in its results.

The oscilloscope’s bandwidth and high sample rate allow it to easily capture high resolution views of signals of interest, making it suitable for measuring and displaying the analog characteristics of electrical signals. Correlating a small number of digital, analog and serial signals, oscilloscopes usually feature two or four input channels.

Meanwhile, logic analyzer is considered the ideal tool for verifying as well as debugging complex digital designs. Its most evident difference with an oscilloscope is the number of input channels. As mentioned earlier, traditional oscilloscopes generally feature two or four channels, while logic analyzers feature 34 input channels to hundreds or even thousands.

They also differ in the manner of acquiring signals. Oscilloscopes sample the signal using an eight-bit analog-to-digital converter (ADC) to generate a faithful reproduction of the signal together with the entire analog subtleties on the display. On the other hand, logic analyzers sample the signal by simply comparing it to a user defined threshold. Thus, if the signal is more than the threshold then it is a Logic 1, and if it is lower, it is considered a Logic 0. These varying acquisition styles result to a single pulse being displayed in different manner.

Oscilloscope and logic analyzer also differ in triggering. Oscilloscope provides basic trigger modes that are focused on isolating anomalous analog characteristics such as runt pulses, glitches and slew rates, and basic digital conditions such as a single logical pattern defined across two or four input channels. On the contrary, logic analyzer offer extensive logic resources including numerous word counters, timers and comparators, allowing the user to define multi-state and complex triggering to isolate problems.

Hosting a full complement of microprocessor support packages, logic analyzers also has the ability to time-correlate and monitor multiple system buses on one instrument.

Realizing the need to view both analog and digital signals, oscilloscope manufacturers have decided to create digital oscilloscope modules for logic analyzers.

These modules are, however, not without limitations. Unlike standalone oscilloscope that functions in real-time, these modules are primarily single-shot devices. They lack the performance of a traditional oscilloscope, don’t come with the familiar oscilloscope user interface and are fairly expensive. They are also not available for general oscilloscope use in everyday debug tasks since they are integrated into the logic analyzer.

Acknowledging the need to correlate data captured through a bench-top oscilloscope with data acquired through a logic analyzer, oscilloscope manufacturers have come up with an integrated two-box solution that allows users to integrate and time-correlate data from an oscilloscope and a logic analyzer.

Unlike the oscilloscope modules, this mixed signal test solution offers the power of a fully functional oscilloscope and logic analyzer acting as one.