Mastering Frequency Response Analysis with the Scopy Network Analyzer

The Scopy Network Analyzer, a powerful tool accessible through the Analog Devices Wiki, provides a versatile platform for analyzing the frequency response of electronic systems. This article delves into the intricacies of using the Scopy Network Analyzer, covering its features, functionalities, and practical applications. Whether you're a student, hobbyist, or professional engineer, understanding this tool can significantly enhance your circuit analysis capabilities.

What is the Scopy Network Analyzer?

The Scopy Network Analyzer is a software instrument designed to work with hardware platforms like the ADALM2000 (M2k) Active Learning Module. It allows users to inject signals into a circuit and measure its response across a range of frequencies. This process, known as frequency response analysis, is crucial for understanding how a circuit behaves under different signal conditions and for verifying its stability.

Navigating the Front Panel

The Scopy Network Analyzer interface is designed for intuitive operation. Here's a breakdown of the key elements:

• Run/Stop and Single Buttons: These control the data acquisition process. "Run" initiates continuous analysis, while "Stop" halts it. "Single" performs a single sweep of the specified frequency range.
• Settings Menu Button: This opens a panel with various configuration options. These settings can be accessed from the right side menu on the display.
• General Settings Menu Button: This button opens settings for plot type, data export and reference importing.
• Cursors Button: This button enables two cursors that can be dragged along the Bode plot to indicate specific points and measurements.

Understanding the Settings Menu

The Settings Menu allows fine-tuning of the network analyzer:

• Reference Channel: Designates the input signal used as a phase reference. Typically, oscilloscope probes 1+ and 2+ are used.
• Waveform Settings:
  • Amplitude: Sets the amplitude of the output signal (1uV to 10V).
  • Offset: Introduces a DC offset to the signal (-5V to 5V).
  • Settling Time: the capture settling time
• Response Settings:
  • DC Filtering.
  • Gain Mode: Configures the gain mode (Automatic, High, Low).
  • Settling time.
• Sweep Settings:
  • Linear/Logarithmic Switch: Selects the scale type for the frequency axis. Helpful when viewing data results.
  • Start/Stop Frequency: Defines the frequency range for the analysis (1mHz to 20MHz).
  • Samples/Decade and Total Samples Count
  • Periods: Sets the minimum number of periods to be acquired
  • Average: Configures the number of averages to be applied to the measurements.
• Display Settings:
  • Allows adjustment of the magnitude (dB) and phase (degrees) ranges for optimal plot visualization. Magnitude can be set from -120 dB to 120 dB. The degrees can be set to any value within -180 to 180 degrees.

Visualizing Data with Plots

The Scopy Network Analyzer offers three primary plot types for frequency response analysis:

• Bode Plot:

  • Displays magnitude (in dB) and phase shift against frequency.
  • Essential for assessing gain and phase margins, crucial for stability analysis.

• Nyquist Plot:

  • A polar plot showing the relationship between magnitude and phase.
  • Helps determine system stability based on the Nyquist stability criterion.

• Nichols Plot:

  • Plots gain magnitude (dB) against phase (degrees).
  • Facilitates graphical determination of gain and phase margins.

Buffer Previewer

• Allows you to view the acquired buffers in a time domain plot. It contains a switch used to turn ON/OFF the buffer previewer and a button which opens the current buffer in the Oscilloscope tool.

Practical Example: Analyzing a Low Pass Filter

Let's illustrate the Scopy Network Analyzer's application with a low-pass filter circuit. The filter is built with a resistor and capacitor. The ADALP2000 Parts kit for Circuits is great for building simple circuits like low pass filters.

1. Circuit Setup: Connect the filter circuit to the ADALM2000 (M2k) Active Learning Module.
2. Connections:
   • Stimulus: Waveform Generator channel 1 (W1).
   • The reference channel measurement: Oscilloscope Positive Channel 1 (+1).
   • Response channel: Oscilloscope Positive Channel 2 (+2).
3. Configuration:
   • Reference Channel: Channel 1.
   • Frequency Range: 1kHz to 10MHz.
4. Analysis: Run the instrument to generate the frequency response plot.

The resulting plot will show the attenuation of the signal's amplitude for frequencies above the cutoff frequency, characteristic of a low-pass filter as shown in the Analog Dialogue. The amplitude of the output signal decreases after the components chosen cutoff frequency. By choosing different components, the cutoff frequency can be adjusted.

Conclusion

The Scopy Network Analyzer is an invaluable tool for anyone involved in circuit design and analysis. By mastering its features and understanding the different plot types, you can gain deep insights into the frequency response of electronic systems. Whether you're evaluating filter performance, assessing amplifier stability, or characterizing complex circuits, the Scopy Network Analyzer empowers you to make informed decisions and optimize your designs. Remember to consult the Analog Devices Wiki for more detailed information and updates on this versatile tool.