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Vector Signal Analyzer (Complex Envelope): VSA



VSA gathers a reference signal and a measured signal for use by many of the multiple input measurements such as AMtoAM_PS or EVM_PS.

VSA can also act as a sweep controller, similar to the Swept Variable Controller block SWPVAR. To do so, specify the variable to be swept in the VARNAME parameter and the values for the sweep in the VALUES parameter. If the block is to control when a new sweep begins, set either the SWPDUR or SWPCNT parameter.

VSA can be used with the Swept Variable Control block (SWPVAR) and the Vector Network Analyzer block (VNA) to perform multi-dimensional sweeps. The SWPVAR documentation describes multi-dimensional sweeps in detail.


Name Data Type Description Unit Type Default
ID N Element ID N/A M
VARNAME S Name of variable to sweep (optional) Text  
VALUES V Vector of values for sweep (in base units, optional) Scalar  
*SWPDUR R Duration of each sweep Time  
*SWPCNT I Samples per sweep Scalar  
*RBW R Resolution bandwidth Frequency  
*VBW R Video bandwidth Frequency  
*NFFT I Number of FFT bins Scalar  
*NAVG I Number of averages Scalar -1
*SLDFRC R Fraction of window to slide Scalar 0.5
*WNDWHN E When to window   Auto
*WNDTYP E FFT windowing type N/A Auto
*WNDPAR R FFT windowing parameter Scalar  
*ZLREF C Load impedance seen at reference signal input (set empty for probe) Resistance  
*ZLMEAS C Load impedance seen at measured signal input (set empty for probe) Resistance  
*SWPVAR R Swept variable (for V5.53 compatibility) Scalar  

* indicates a secondary parameter

Parameter Details

VARNAME. The name of an optional variable to be swept. This should be in double quotation marks, such as "A". There must be a corresponding equation on the system diagram with a dummy numerical value assigned to it, such as "A=0". In order to affect the simulation results, the variable must be used as a parameter in one or more blocks, either directly or through other equations.

VALUES. The optional vector of real values for each sweep. The vector is enclosed in brackets, as in: {0,1,2}. The stepped() built-in function can be used to create a set of equally spaced values.

SWPDUR. The minimum duration of each sweep. Either this or SWPCNT can specify the duration of each sweep.

SWPCNT. The minimum number of samples to gather for each sweep. Either this or SWPDUR can specify the duration of each sweep.

RBW. The default resolution bandwidth for spectrum-based measurements. The spectrum based measurements approximate the number of points for the FFTs from NFFT = SMPFRQ / RBW. Either this or NFFT can control the spectrum frequency resolution.

VBW. The default video bandwidth for spectrum-based measurements. The video bandwidth in a spectrum analyzer is the bandwidth of the video filter, which is a lowpass filter normally used to smooth the spectrum display. Smaller video bandwidths result in a smoother displays. The spectrum-based measurements approximate the effect of the lowpass filter by performing FFT averaging. The number of averages is set from NAVG = RBW / VBW. Either this or NAVG can control spectrum smoothing.

NFFT. The default number of FFT bins to use for spectrum-based measurements. Either this or RBW can control the spectrum frequency resolution.

NAVG. The default number of averages to use for spectrum-based measurements. If set to 0, measurements use cumulative averaging. Either this or VBW can control spectrum smoothing.

WNDTYP. The default type of windowing to perform for the FFT computations used by frequency domain based measurements. When windowing is applied is determined by the WNDWHN parameter.

WNDPAR. The default windowing parameter used for the window type selected by WNDTYP.

SLDFRC. The default percentage of the time domain data window by which averaged FFTs are overlapped. A value of 1 indicates no overlapping, a value of 0.75 indicates 25% overlap, and a value of 0.5 indicates 50% overlap.

WNDWHN. Determines when windowing is applied to FFT computations. When set to Auto, data windowing is only performed when averaging is being performed.

ZLREF. The impedance seen looking into the reference signal input node. Leave empty to treat the node as a voltage probe.

ZLMEAS. The impedance seen looking into the measured signal input node. Leave empty to treat the node as a voltage probe.

SWPVAR. This is for backward compatibility with version 5.53. If both SWPDUR and SWPCNT are empty and this is assigned a swept variable, the VSA block will automatically sweep the simulation. This is provides some backward compatibility with version 5.53, in which this block performed simulation sweeps when an AVGCH_INPDB measurement was specified with a sweep count. In 6.0, all sweeping is controlled within the system diagram blocks, not within the measurements.

Data Input

Node No. Type Purpose
1 Complex Reference Signal
2 Complex Measured Signal

Implementation Details

If a sweep duration is specified through either SWPDUR or SPWCNT, the duration represents a basic minimum number of samples to receive before requesting a sweep of the simulation. If there is a signal delay present in the measured signal, the equivalent number of samples is added to this minimum. There is also an absolute minimum number of samples determined by the RBW/NFFT, VBW/NAVG and SMPFRQ parameters. These determine the minimum number of samples required by measurements with default settings that perform spectrum-based computations.

Recommendations for Use

The Vector Network Analyzer block (VNA) performs a similar function except it generates the tone signal internally.

When using ZLREF and/or ZLMEAS, blocks connected to the input nodes will only see ZLREF or ZLMEAS if impedance mismatch modeling has been enabled through the System Options dialog box. Measurements, however, always use ZLREF or ZLMEAS, if specified, when computing power. See Chapter 2 details on impedance mismatch modeling.

The parameters such as RBW, VBW, NFFT and NAVG are typically used to establish system diagram-wide settings for these parameters. For example, to set a default RBW of 10 kHz, you could create an equation such as: RBW_Hz=10e3

You can then assign it to the RBW parameter for all TP, VNA, and VSA blocks. Any spectrum-based measurement that refers to one of these blocks uses that RBW setting by default.

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