An oscilloscope is a diagnostic and measurement instrument used not only in laboratories by chemists and physicists or in service centers by engineers. Oscilloscopes are applied wherever there is a need to measure or control the waveform of electrical voltages and current over time. By using transducers, which are devices that convert measured physical quantities (such as pressure or temperature) into voltage, the range of oscilloscope applications is very broad.
Real-Time Oscilloscopes
A real-time oscilloscope captures the entire waveform with each triggering event. This means that a large number of data points are recorded in a single continuous recording. The sampling rate determines the intervals between samples, and memory depth determines the number of points that will be displayed.
To capture any waveform, the sampling rate must be significantly faster than the frequency of the incoming waveform. Real-time oscilloscopes (RTO) are designed to provide a sufficiently high sampling rate, enabling the capture of transient and non-repetitive signals within the device's specified analog bandwidth. Another feature of a real-time oscilloscope is its ability to capture a continuous signal with a single acquisition. Real-time oscilloscopes are suitable for analyzing non-repetitive signals, such as varying event occurrence speeds.
As the name suggests, a real-time oscilloscope records the signal in digital form in real-time. It samples the signal quickly enough to accurately capture and display it. Each data point on the display is sampled directly after the previous one.
Real-time oscilloscopes, also known as Digital Storage Oscilloscopes (DSO) or Mixed-Signal Oscilloscopes (MSO), are currently the most common oscilloscopes on the market. They can operate in bandwidths ranging from a few MHz to several tens of GHz, and their prices range from a few hundred to hundreds of thousands of dollars.
Sampling Oscilloscopes
Sampling oscilloscopes, also known as Digital Communications Analyzers (DCA), offer bandwidths reaching several tens of GHz. They are primarily used for analyzing high-speed serial buses and optical devices. As bandwidth increases, sampling oscilloscopes and real-time oscilloscopes begin to overlap in several application areas.
However, sampling oscilloscopes allow the measurement of rapidly changing signals in a very wide frequency range. Their limitation is the ability to observe only repetitive signal waveforms. These devices sample the input signal's voltage and store it. With each subsequent signal, the input gate opens for a very short time with a time delay. Combining all the sampled points allows the reconstruction of the input signal. A key feature of these oscilloscopes is the repeated capture of individual values at different moments. Accurate waveform reconstruction requires a repetitive signal pattern.
Sampling oscilloscopes are used to capture, display, and analyze repetitive signals. Triggering is set for these signals, and when the first triggering condition is met, the sampling oscilloscope captures a set of non-contiguous samples within a specified time interval. Then, the oscilloscope delays the trigger point and begins another set of captures, placing the captured points on the display along with the first set of samples. Repeating this operation creates a waveform that does not need to be acquired continuously.
Applications
One of the key advantages of real-time oscilloscopes compared to sampling oscilloscopes is their versatile support for decoding and testing many protocols and standards. For example, Keysight's InfiniiVision series oscilloscopes belong to this category. Keysight's Infiniium real-time oscilloscopes are equipped with software that enables decoding, debugging, and compliance testing for many modern communication protocols. These protocols are crucial for the industry and include, among others, the latest generations of USB, DDR, and PCI Express.
Sampling oscilloscopes in Keysight's portfolio are called digital communication analyzers. The name itself emphasizes their ability to characterize high-speed digital signals used in data centers and telecommunications systems. The Keysight DCA series offers the highest measurement accuracy in the industry for advanced digital designs.
