What Are Sampling Oscilloscopes?
An oscilloscope is a type of electrical measuring instrument that displays changes in electrical signals (voltages) over time as waveforms.
Sampling oscilloscopes, also known as Equivalent Time Sampling Oscilloscopes, are specialized for measuring high-speed signals. They differ from traditional oscilloscopes as they lack attenuators and amplification circuits in the previous stage, enabling more accurate high-speed signal analysis.
Uses of Sampling Oscilloscopes
The primary use of oscilloscopes is to monitor changes in electrical signals. In addition to voltage, they can measure various phenomena such as temperature, humidity, speed, and pressure. Sampling oscilloscopes are particularly adept at measuring high-speed electrical and optical signals, and are invaluable in TDR (Time Domain Reflectometry) for evaluating digital signal quality on printed circuit boards and cables, as well as in LSI performance and defect analysis.
Principles of Sampling Oscilloscopes
Sampling oscilloscopes capture and convert voltages into digital data using A/D converters, storing this data in memory and displaying it on the screen as waveforms. The input portion consists of a vertical circuit and a trigger system, converting the signal in the preceding stage. These oscilloscopes use equivalent-time sampling, capturing part of the waveform in a single cycle and reconstructing the full waveform over multiple cycles. This method achieves high time resolution, surpassing the actual sampling period, enabling the measurement of high-speed signals.
Supported Standards for Sampling Oscilloscopes
Sampling Oscilloscopes support various standards suitable for capturing high-speed signals, such as:
- Ethernet: 10Gb interface standard specified in IEEE802.3ae.
- SDH/SONET: 10Gb interface standard specified by ITU-T.
- OTN: Optical transmission network standard specified by ITU-T.
- Fiber Channel: 10Gb interface standard specified by ANSI.
- InfiniBand: Used for ultra high-speed connections, with standards ranging from SDR to EDR, supporting up to 300 Gbps.
- CPRI: Communication standard prevalent up to 4G, with rates from 1.2288 Gbit/s to 9.8304 Gbit/s.
Interfaces for Sampling Oscilloscopes
Key interfaces for sampling oscilloscopes include:
- Differential electrical: Utilizes two wires for signal detection, comprising the source signal and its phase-reversed counterpart.
- Optical: Enables evaluation without a trigger signal by connecting an optical module or optical transmission device.
Measurement Examples Where Sampling Oscilloscopes Are Used
Sampling oscilloscopes are commonly used in optical module evaluation, including:
- Eye pattern analysis: This involves analyzing eye pattern waveforms by adding periodic signal waveforms.
- Eye mask test: Tests whether the eye pattern meets the aperture ratio required by each standard.
- TDECQ measurement: Assesses the quality of PAM4 optical signals.