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Where To Find This Example

Select Help > Open Examples... from the menus and type either the example name listed above or one of the keywords below.

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Design Notes

16QAM EVM and IQ Imbalance

This example demonstrates the impact of phase imbalance, amplitude imbalance, and dc-offset on the RMS Max EVM measurement.

The resulting constellation of the RF link is shown in "16QAM IQ after RF link".

The best EVM (approximately 1.0%) is achieved when all imbalances are set to zero.  The EVM measurement can be monitored in the "EVM Measured in percentage" table.

The example makes use of the VSS RMS EVM measurement, and the I_Q imbalance model. The I_Q imbalance model is a subcircuit and can be found in the elements tree under Libraries/RF Blocks.

In this example, you can tune on the average signal power (PWR), phase imbalance (PHASE) and amplitude imbalance (AMPLITUDE).

To update the MWO Filter Response graph you have to click the Analyze button.

The DLYCMP block is used to compensate for the group delay of the filter.

The ALIGN block applies a constant gain and phase correction to the distorted signal from the RF link. The correction is determined from an initial block of reference and distorted samples.

Please read the online help for each block and measurement along with the VSS Getting Started Guide. You can find the VSS Getting Started Guide under Help --> Getting Started.

System Diagram - 16QAM Signal EVM Test Bench

Schematic - Filter

Graph - Average Signal Power in dBm

DB(PWR_vsT(TP.64QAM_IN,0,0,0,0,1,1000,0,30,1,-1,0,-1,10,1,0,0.5,0,0,0,0,0)) (us) 16QAM Signal EVM Test Bench Time DB(PWR_vsT(TP.64QAM_IN,0,0,0,0,1,1000,0,30,1,-1,0,-1,10,1,0,0.5,0,0,0,0,0)) (dBm) 16QAM Signal EVM Test Bench
617.086 -4.36657

Graph - EVM Measured in percentage

EVM(VSA.M1,0,1,1,100,1,0,10,0,0,0,1,1,0,0,0,0) (us) 16QAM Signal EVM Test Bench Time EVM(VSA.M1,0,1,1,100,1,0,10,0,0,0,1,1,0,0,0,0) 16QAM Signal EVM Test Bench
599.844 11.3222

Graph - Circuit Filter Response