Determining the Phase Response of a Frequency Sweep in SignalExpress
Primary Software: LabVIEW Signal Express>>Development System
Primary Software Version: 1.0
Primary Software Fixed Version: N/A
Secondary Software: N/A
Problem: How can I determine the phase response of a frequency sweep (of a filter, for example) in SignalExpress?
Solution: There are two options for determining the phase response of a frequency sweep in SignalExpress:
- Option 1: Determine Phase Response from the Frequency Sweep Operation
To determine the phase response from your frequency sweep example (a filter), you would first need to simultaneously sample the excitation and response signals from the filter using a digitizer (or equivalent simultaneously sampling hardware). Next you would use the Tone Extraction step to extract the detected phase of each signal. A Formula step would then be used to calculate the phase response between the input and output phase measurements (see attached Example 1 - Note: Use 'Run Once' mode.). In this scenario, a user defined step that takes in the excitation and response signals and simply returns the magnitude and phase response is a much simpler and more flexible approach to performing a phase response within the frequency sweep loop (see attached Example 2 - Note: Use 'Run Once' mode). In this case the user defined step uses a LabVIEW VI (also attached) to perform the tone extraction and phase response calculations required for the measurement, which greatly simplifies the measurement task.
Option 2: Determine Phase Response from the Frequency Response Step (without Sweep Operation)
Alternatively, a Frequency Response step could be used to perform the necessary amplitude and phase response measurements based on excitation and response signals of the circuit without using a sweep operation (see attached Example 3 - Note: Use 'Run' mode to see continuous averaging). The built-in Frequency Response step reduces the complexity of performing this measurement and results in a faster time to measurement; however, it also reduces the dynamic range of the measurement since it is performing parallel analysis across the entire range of frequencies in the signal. It also limits the user to a linear range of frequencies used in the frequency response as opposed to Example 2 which permits linear, exponential, or user defined points for the frequency sweep. Example 2 also avoids sacrificing the dynamic range of the amplitude and phase response since it calculates the measurements on a frequency by frequency basis rather than all at once.
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Report Date: 05/11/2005
Last Updated: 05/12/2005
Document ID: 3LA7QTL2
