Phase Noise Analysis in VCO

This example shows how to measure and analyze the effect of phase noise in a voltage controlled oscillator (VCO). Using a VCO block and VCO testbench, this example defines the typical phase noise levels from datasheet specifications and validates the VCO.

Set Up VCO Testbench Model

Open the model vcoPhaseNoiseAnalysis . The model consists of a VCO block and a VCO Testbench.

open_system('vcoPhaseNoiseAnalysis.slx')

VCO Specifications and Phase Noise Impairments

Double click the VCO block to open the Block Parameters dialog box. In the Configuration tab, the Voltage Sensitivity (Hz/V) is set to 125e6. In the Impairment tab, check that the Add phase noise option is enabled. Phase noise frequency offset (Hz) and Phase noise level (dBc/Hz) parameters represent a typical phase noise profile in a VCO.

Modify VCO Testbench According to VCO Specifications

Double click the VCO Testbench block to open the Block Parameters dialog box. In the Stimulus tab, Control voltage (V) is set to 4.

Since the VCO has a sensitivity of 1 MHz/V and the free running frequency of 2.5 GHz, the operating frequency of the VCO is 3 GHz. In the Setup tab, the Sampling frequency (Hz) is set to 24e9, which is eight times the target operating frequency. Also check that in the Target Metric tab, the Phase noise frequency offset (Hz) and Phase noise level (dBc/Hz) parameters match the values set in the VCO block.

Plot Phase Noise Profile

Run the simulation for 1.2 ms, according to the Recommmended min. simulation stop time (s) in the Block Parameters dialog box of VCO Testbench.

Once the simulation is complete, the phase noise profile is displayed on the icon of the VCO Testbench. The measured phase noise is comparable to target phase noise.

In the Block Parameters dialog box of VCO, click the Plot measurement button to plot the phase noise profile of the VCO. Notice that the VCO operating frequency is 3 GHz, and that the measured and targeted phase noise profiles match.