Oscilloscope Types: DSO, DPO, and Digital Sampling

This article explores the differences between three common types of digital oscilloscopes: Digital Storage Oscilloscopes (DSO), Digital Phosphor Oscilloscopes (DPO), and Digital Sampling Oscilloscopes. While both analog and digital oscilloscopes analyze analog voltage waveforms over time, digital oscilloscopes utilize an Analog-to-Digital Converter (ADC), a microprocessor, and acquisition memory to display signals. This conversion to a digital format is what classifies them as “digital.” You can also refer to this resource on Analog Oscilloscope Vs Digital Oscilloscope.

The internal structure of a digital oscilloscope leads to the three main types we’ll discuss:

• Digital Storage Oscilloscope (DSO)
• Digital Phosphor Oscilloscope (DPO)
• Digital Sampling Oscilloscope

Let’s delve into the key differences between these types.

Digital Storage Oscilloscope (DSO)

Figure 1: Block Diagram of a Digital Storage Oscilloscope

Here are some key features of a DSO:

• Screen Type: Uses a raster-type screen for display.
• Event Capture: Ideal for capturing and analyzing single-time or transient events.
• Waveform Storage: Waveforms are stored in digital binary form, enabling analysis both within the oscilloscope and on external computers.
• Processing Architecture: Employs a serial processing architecture as shown in Figure 1.
• Microprocessor Function: The microprocessor handles signal processing and also manages the front panel controls of the device.
• Applications: Well-suited for low repetition rate or single-shot applications, high-speed measurements, and multi-channel analysis.

Digital Phosphor Oscilloscope (DPO)

Figure 2: Block Diagram of a Digital Phosphor Oscilloscope

Here’s what makes a DPO unique:

• Processing Architecture: Uses a parallel architecture for faster operation.
• Hardware Acceleration: Employs ASIC-based hardware to acquire waveforms, enabling higher capture rates.
• Transient Analysis: High capture rates make DPOs excellent for analyzing transient events such as glitches and transition errors.
• Speed: Generally performs faster than DSOs due to its parallel processing.
• Data Storage: Utilizes a pure electronic digital phosphor as its database.

Digital Sampling Oscilloscope

Figure 3: Block Diagram of a Digital Sampling Oscilloscope

Here are the defining characteristics of a digital sampling oscilloscope:

• High-Frequency Measurement: Designed for measuring high-frequency signals where frequency components exceed the oscilloscope’s normal sampling rate.
• Speed: Considered the fastest type of oscilloscope.
• Bandwidth: Available with bandwidths up to 80 GHz.
• Amplification: Unlike DSOs and DPOs, a sampling oscilloscope uses an amplifier after the sampling stage.
• Dynamic Range: A sampling bridge is used to achieve the oscilloscope’s dynamic range, which is typically limited to about 1 Volt (peak-to-peak). In contrast, DSOs and DPOs generally offer a dynamic range of 50 to 100 Volts.
• Input Voltage Limits: Due to the design constraints (a diode can’t be used before the sampling bridge), the safe input voltage limit is very low (about 3V). DSOs and DPOs can handle input voltages up to 500 Volts safely.

In summary, each type of digital oscilloscope caters to different needs based on speed, signal type, and measurement requirements. Choosing the right type depends heavily on the specific application and the signals you need to analyze.