VCO Testbench

Validate voltage controlled oscillator (VCO) by measuring phase noise metrics or VCO characteristics

• 

Libraries:
Mixed-Signal Blockset / PLL / Measurements & Testbenches

Description

The VCO Testbench block validates the VCO device under test (DUT) by measuring one of the two target metrics: phase noise, or voltage sensitivity and quiescent frequency. You can use the testbench to validate a VCO of your own implementation, or you can use the VCO block from the Mixed-Signal Blockset™.

The VCO Testbench block generates the stimulus (control voltage) to drive the device under test (DUT) from the Stimulus tab. The setup parameters for validating the DUT are defined in the Setup tab and the target validation metrics are defined in the Target Metric tab.

To take the full advantage of the VCO testbench capabilities by using autofill parameters options, use only two blocks, the VCO DUT and the VCO Testbench in the Simulink^® model.

Examples

Finding Voltage Sensitivity and Quiescent Frequency of VCO

Find VCO metrics such as voltage sensitivity (Kvco) and quiescent frequency or free running frequency (Fo).

• Open Script

Measuring VCO Phase Noise to Compare with Target Profile

Validate the phase noise profile of a VCO device under test (DUT) using a VCO Testbench.

• Open Script

Ports

Input

from vco — Input signal

scalar

Input signal, which flows from the output of the VCO DUT. This input signal is used to calculate either the phase noise metric, or the voltage sensitivity and free running frequency of the VCO, depending on the Measurement option chosen.

Data Types: double

Output

to vco — Output signal

scalar

Output signal, which provides control voltage stimulus to the input of VCO DUT.

Data Types: double

Parameters

Measurement — Target metric to be measured

Phase noise (default) | Kvco and Fo

Determines which of the two given target metrics is being measured.

Select Phase noise if you want the testbench to measure and compare phase noise to a target phase noise profile.

Select Kvco and Fo if you want the testbench to compute voltage sensitivity (K_vco) and quiescent frequency (F_o) using a range of control voltages.

Programmatic Use

• Use get_param(gcb,'MeasureOptions') to view the current Measurement option.

• Use set_param(gcb,'MeasureOptions',value) to set Measurement to a specific option.

Set stop time — Set recommended minimum simulation stop time as model stop time

button

Click to set the Recommended min. simulation stop time (s) reported by the VCO Testbench block as the model stop time.

Dependencies

This button is only available when you select Phase noise as the Measurement option.

Plot measurement — Plot measurements

button

Plots the relevant VCO metrics based on the Measurement options.

Selecting Phase noise in Measurement plots phase noise profile of VCO.

Selecting Kvco and Fo in Measurement plots the VCO characteristics and K_vco.

Export measurement results — Export measurement results

button

Exports the relevant VCO metrics based on the Measurement options to an excel file.

Selecting Phase noise in Measurement exports the phase noise profile of VCO.

Selecting Kvco and Fo in Measurement exports the VCO characteristics and K_vco.

Stimulus

Control voltage (V) — VCO control voltage

2 (default) | scalar

Control voltage provided by VCO Testbench, expressed as a scalar in V. The value specified in Control Voltage (V) flows through the to vco port that provides the input of VCO.

Dependencies

To enable this parameter, select Phase noise as the Measurement option.

Programmatic Use

• Use get_param(gcb,'ControlVoltage') to view current Control Voltage (V) value.

• Use set_param(gcb,'ControlVoltage',value) to set Control Voltage (V) to a specific value.

Data Types: double

Range of control voltage (V) — Range of VCO control voltages

[2 7] (default) | two-element row vector

Control voltage provided by VCO Testbench, expressed as a two-element row vector in V. This parameter specifies the minimum and maximum values of control voltage, which is used to generate ten control voltage value points, including the provided values. These ten values of control voltage are sent to VCO input to measure K_vco and F_o.

Dependencies

To enable this parameter, select Kvco and Fo as the Measurement option.

Programmatic Use

• Use get_param(gcb,'ControlVoltageRange') to view the current Range of control voltage (V) values.

• Use set_param(gcb,'ControlVoltage',value) to set Range of control voltage (V) to specific values.

Data Types: double

Setup

Autofill setup parameters — Automatically calculate setup parameters for phase noise measurement

button

Click this button to automatically populate setup parameters ( Resolution bandwidth (Hz) and No. of spectral averages) for phase noise measurement.

If the DUT is a VCO from Mixed-Signal Blockset, the dsp.SpectrumEstimator System object™ used by the VCO Testbench block for phase noise measurement automatically calculates setup parameters based on the VCO specifications.

Dependencies

• This button only works if the VCO DUT is a VCO block from Mixed-Signal Blockset.

• This button is only available when you select Phase noise as the Measurement option.

Resolution bandwidth (Hz) — Smallest positive frequency that can be resolved

30e3 (default) | real positive scalar

Smallest positive frequency that can be resolved, specified as a real positive scalar. The Resolution bandwidth (Hz) is used to determine window length for spectral analysis using the Welch method. For more information, see Welch's Method of Averaged Modified Periodograms.

In general, Resolution bandwidth (Hz) should be less than or equal to the lowest offset frequency value.

If the DUT is a VCO block from the Mixed-Signal Blockset library, you can use the Autofill setup parameters button to automatically calculate Resolution bandwidth (Hz).

Dependencies

To enable this parameter, select Phase noise as the Measurement option.

Programmatic Use

• Use get_param(gcb,'ResBandwidth') to view current Resolution bandwidth (Hz) value.

• Use set_param(gcb,'ResBandwidth',value) to set Resolution bandwidth (Hz) to a specific value.

Data Types: double

No. of spectral averages — Number of spectral averages

8 (default) | positive integer scalar

Number of spectral averages, specified as a positive integer scalar. The dsp.SpectrumEstimator System object used by the Phase Noise Measurement subsystem inside the VCO Testbench block computes the current power spectrum or power density spectrum estimate by averaging over the number specified by No. of spectral averages.

If the DUT is a VCO block from the Mixed-Signal Blockset library, you can use the Autofill setup parameters button to automatically calculate number of spectral averages.

Dependencies

To enable this parameter, select Phase noise as the Measurement option.

Programmatic Use

• Use get_param(gcb,'SpectralAverages') to view current No. of spectral averages value.

• Use set_param(gcb,'SpectralAverages',value) to set No. of spectral averages to a specific value.

Data Types: double

Hold-off time (s) — Delays measurement analysis to avoid transients

0 (default)

Hold-off period, specified as a nonnegative scalar in s. Hold-off time delays measurement analysis by the specified amount of time to avoid corrupting simulation results due to transients.

Programmatic Use

• Use get_param(gcb,'HoldOffTime') to view the current Hold-off time (s) value.

• Use set_param(gcb,'HoldOffTime',value) to set Hold-off time (s) to a specific value.

Target Metric

Autofill target metric — Automatically populate target phase noise metric

button

Click this button to automatically populate the target phase noise metric from VCO specifications.

Dependencies

• This button will only work if the VCO DUT is a VCO block from Mixed-Signal Blockset.

• This button is only available when you select Phase noise as Measurement option.

Phase noise frequency offset vector (Hz) — Phase noise frequency offset vector

[30e3 100e3 1e6 3e6 10e6] (default) | real valued vector

The frequency offsets of phase noise from the carrier frequency, collected from the data sheet, specified as a real valued vector in Hz.

If the DUT is a VCO block from the Mixed-Signal Blockset library, you can use the Autofill target metric button to automatically transfer VCO phase noise frequency offset vector values to the VCO Testbench.

Dependencies

To enable this parameter, select Phase noise as the Measurement option.

Programmatic Use

• Use get_param(gcb,'PhaseNoiseFreqOffset') to view the current Phase noise frequency offset vector (Hz) value.

• Use set_param(gcb,'PhaseNoiseFreqOffset',value) to set Phase noise frequency offset vector (Hz) to a specific value.

Data Types: double

Phase noise vector (dBc/Hz) — Phase noise vector

[-45 -55 -65 -75 -100] (default) | real valued vector

The phase noise power in a 1 Hz bandwidth centered at the specified frequency offsets relative to the carrier, collected from the data sheet, specified as a real valued vector in dBc/Hz. The elements of Phase noise vector (dBc/Hz) corresponds to relative elements in the Phase noise frequency offset vector (Hz).

If the DUT is a VCO block from the Mixed-Signal Blockset library, you can use the Autofill target metric button to automatically transfer VCO phase noise vector values to the testbench.

Dependencies

To enable this parameter, select Phase noise as the Measurement option.

Programmatic Use

• Use get_param(gcb,'PhaseNoiseVector') to view the current Phase noise vector (dBc/Hz) value.

• Use set_param(gcb,'PhaseNoiseVector',value) to set Phase noise vector (dBc/Hz) to a specific value.

More About

Inside VCO Testbench

The VCO Testbench subsystem block consists of a Step block and a subsystem that contains two variants: a Phase-noise measurement subsystem and a Frequency detector subsystem. The variant subsystems are enabled based on the selection of the Measurement option in the block parameters dialog box.

Inside the Step block, the Step time is set to Hold-off time (s) value and delays the measurement analysis by the specified time.

Phase Noise Measurement

The Phase-noise subsystem is activated when Phase noise is selected as the Measurement option. The subsystem uses the zero crossing points of a signal to measure the phase noise. From the zero crossing points, the phase error (φ)is extracted both at the rising and falling edge of the signal. The captured phase error is used to generate a periodic signal (sin(φ)). This periodic signal is interpolated using a fixed time step proportional to the maximum phase noise frequency offset. The power density of the modified phase noise signal, using the dsp.SpectrumEstimator System object, directly provides the phase noise profile of the signal of interest.

Voltage Sensitivity and Free Running Frequency Measurement

The Frequency detector subsystem is activated when Kvco and Fo is selected as the Measurement option. The subsystem spreads the range of control voltage over 10 points using their minimum and maximum values. A VCO characteristics curve is generated for each point. Voltage sensitivity (K_vco) is calculated by taking the average of slopes between each points. Quiescent frequency (F_o) is extrapolated at control voltage zero.

References

[1] Banerjee, Dean. PLL Performance, Simulation and Design. Indianapolis, IN: Dog Ear Publishing, 2006.

Version History

Introduced in R2019a