Functional Comparison between Logic Analyzer and Oscilloscope

Functional Comparison between Logic Analyzer and Oscilloscope

Since its birth, logic analyzers often give people three impressions:

① Expensive and difficult to operate;

②High requirements for users;

③It has similar functions to an oscilloscope, except that it has more channels and some timing functions.

In fact, logic analyzers and oscilloscopes are now merging and have also undergone significant differences in testing principles. In addition, with the development of IT technology, acquisition-type virtual logic analyzers based on computer interface technology and processing technology have emerged. Logic analyzers have gradually reduced their costs and entered ordinary research laboratories. Logic analyzers, like oscilloscopes, have gradually become basic testing tools.

In the field of electronic testing, the oscilloscope is the earliest test equipment, which originated from the radar scanning principle. The acquisition and reproduction of signal waveforms are based on the traditional testing basis of analog signals and analog circuits. With the development of digital technology, digital signal testing is becoming more and more important. The earliest digital signal testing was often done with oscilloscopes. Later, timing analyzers and state analyzers appeared to analyze and test multiple digital signals from the perspective of timing and state. Because the timing analyzers and state analyzers were expensive at the time, the concepts of the two in the market were good, but the impact was not great, and the test range was very narrow. With the development of digital testing technology, logic analyzers that integrate digital timing and state analysis were born.

A logic analyzer is an instrument that uses a clock to collect and display digital signals from test equipment. Its main function is to determine the timing. Since a logic analyzer does not have many voltage levels like an oscilloscope, it usually only displays two voltages (logic 1 and 0). Therefore, after setting the reference voltage, the logic analyzer will determine the measured signal through a comparator. Those higher than the reference voltage are High, and those lower than the reference voltage are Low, forming a digital waveform between High and Low. For example: a signal to be measured uses a logic analyzer with a sampling rate of 200MHz. When the reference voltage is set to 1.5V, the logic analyzer will take a point every 5ns on average during measurement. Those above 1.5V are High (logic 1), and those below 1.5V are Low (logic 0). The subsequent logic 1 and 0 can be connected into a simple waveform, and engineers can find abnormal errors (bugs) in this continuous waveform. In general, when a logic analyzer measures a measured signal, it does not display the voltage value, but only the difference between High and Low; if you want to measure voltage, you must use an oscilloscope. In addition to the different display of voltage values, another difference between logic analyzers and oscilloscopes is the number of channels. A general oscilloscope has only 2 or 4 channels, while a logic analyzer can have 16 channels, 32 channels, 64 channels, and hundreds of channels. Therefore, a logic analyzer has the advantage of performing multi-channel tests at the same time.
According to the differences in hardware device design, the logic analyzers currently on the market can be roughly divided into stand-alone (or stand-alone) logic analyzers and PC-based card-based virtual logic analyzers that need to be combined with a computer. Stand-alone logic analyzers integrate all test software, computing management components, and other components into one instrument; card-based virtual logic analyzers need to be used with a computer, and the display screen is also separated from the host. In terms of overall specifications, stand-alone logic analyzers have developed into products of quite high standards, such as sampling rates of up to 8GHz, channels that can be expanded to more than 300 channels, and relatively high storage depth. Stand-alone logic analyzers used to be expensive, ranging from tens of thousands to hundreds of thousands of RMB, and ordinary users rarely afford them. Recently, Taiwan OItek Technology Co., Ltd. launched the OLA2032BTM independent desktop EasyDebugTM logic analyzer, which is less than 20,000 yuan and affordable for every engineer. Especially in the teaching of digital circuits, it has changed the problems of teachers using virtual logic analyzers to reduce costs, which led to unintuitive and troublesome problems. At the same price, we can easily pick up a desktop independent logic analyzer. The card-based virtual logic analyzer based on the computer interface provides corresponding performance at a lower cost, but the card-based virtual logic analyzer also has great disadvantages. It needs to be equipped with a computer to use. Especially in digital testing, engineers often get stuck in a pile of PCB boards. Instruments with rotary buttons are more convenient than moving the mouse on the screen. The development of technology has gradually integrated the functions of oscilloscopes and logic analyzers into a hybrid instrument (MSO), also known as a mixed signal test instrument. The comparison between logic analyzer and oscilloscope is as follows, so that we will know when to use a logic analyzer or oscilloscope.

Table 1 Functional comparison between logic analyzer and oscilloscope