VCO

Model voltage controlled oscillator

• Library:

• Mixed-Signal Blockset / PLL / Building Blocks

• 

Description

VCO or voltage controlled oscillator is a voltage to frequency converter. It produces an output signal whose frequency is controlled by the voltage at the input vctrl port. The frequency of the output signal, F is determined either by:

$$F=\left(K_{VCO}·V_{ctrl}\right)+F_o$$

where:

• K_vco = voltage sensitivity (in Hz/V)

• V_ctrl = control voltage (in V)

• F_o= free running frequency (in Hz)

or from linear interpolation using the mapping:

$$F=\text{interp}\left(F_{out}\left(V_{cntl}\right)\right)$$

where:

• V_ctnl = vector of control voltages (in V)

• F_out= vector of corresponding output frequencies (in Hz)

Ports

Input

vctrl — Voltage used to control VCO output frequency

scalar | vector

VCO control voltage used to control the output frequency of the VCO. In a phase-locked loop (PLL) system, vctrl is the output of the Loop Filter that contains the phase error information.

Data Types: double

Output

vco out — Output signal determined by vctrl port

scalar

Output signal of VCO. In a PLL system, vco out is the output clock generated by the PLL. It is also fed back to the PFD block through a clock divider to complete the control loop.

Data Types: double

Parameters

Parameters

Specify using — Define how VCO output frequency is specified

Voltage sensitivity (default) | Output frequency vs. control voltage

Define how VCO output frequency is specified:

• Select Voltage sensitivity to specify output frequency from Voltage sensitivity (Hz/V) and Free running frequency (Hz).

• Select Output frequency vs. control voltage to interpolate output frequency from Control voltage (V) vector versus Output frequency (Hz) vector.

Programmatic Use

Block parameter: SpecifyUsing

Type: character vector

Values: Voltage sensitivity | Output frequency vs. control voltage

Default: Voltage sensitivity

Voltage sensitivity (Hz/V) — Measure of change in output frequency of VCO

100e6 (default) | positive real scalar

Measure of change in output frequency for input voltage change, specified as a positive real scalar with units in Hz/V. This parameter is also reported as VCO voltage sensitivity in the Loop Filter tab and is used to automatically calculate the filter component values of the loop filter.

Dependencies

To enable this parameter, select Voltage sensitivity in Specify using in the Parameters tab.

Programmatic Use

Block parameter: Kvco

Type: character vector

Values: positive real scalar

Default: 100e6

Data Types: double

Free running frequency (Hz) — VCO output frequency without control voltage

2.5e9 (default) | positive real scalar

Frequency of the VCO without any control voltage input (0 V), or the quiescent frequency, specified as a positive real scalar in Hz.

Dependencies

To enable this parameter, select Voltage sensitivity in Specify using in the Parameters tab.

Programmatic Use

Block parameter: Fo

Type: character vector

Values: positive real scalar

Default: 2.5e9

Data Types: double

Control voltage (V) — Control voltage values

[-5 0 5] (default) | real valued vector

Control voltage values of the VCO, specified as a real valued vector in volts.

Dependencies

To enable this parameter, select Output frequency vs. control voltage in Specify using in the Parameters tab.

Programmatic Use

Block parameter: ControlVoltage

Type: character vector

Values: real valued vector

Default: [-5 0 5]

Data Types: double

Output frequency (Hz) — VCO output frequency values

[2e9 2.5e9 3e9] (default) | positive real valued vector

Output frequency of the values of the VCO, corresponding to the Control voltage (V) vector, specified in Hz.

Dependencies

To enable this parameter, select Output frequency vs. control voltage in Specify using in the Parameters tab.

Programmatic Use

Block parameter: OutputFrequency

Type: character vector

Values: positive real valued vector

Default: [2e9 2.5e9 3e9]

Data Types: double

Output amplitude (V) — Maximum amplitude of the VCO output voltage

1 (default) | positive real scalar

Maximum amplitude of the VCO output voltage, specified as a positive real scalar.

Programmatic Use

Block parameter: Amplitude

Type: character vector

Values: positive real scalar

Default: 1

Data Types: double

Enable increased buffer size — Enable increased buffer size

off (default) | on

Select to enable increased buffer size during simulation. This increases the buffer size of the Variable Pulse Delay block inside the VCO block. By default, this option is deselected.

Buffer size — Number of samples of the input buffering available during simulation

10 (default) | positive integer scalar

Number of samples of the input buffering available during simulation, specified as a positive integer scalar. This sets the buffer size of the Variable Pulse Delay block inside the VCO block.

Selecting different simulation solver or sampling strategies can change the number of input samples needed to produce an accurate output sample. Set the Buffer size to a large enough value so that the input buffer contains all the input samples required.

Dependencies

To enable this parameter, select Enable increased buffer size.

Programmatic Use

Block parameter: NBuffer

Type: character vector

Values: positive integer scalar

Default: 10

Data Types: double

Impairments

Add phase noise — Add phase noise as a function of frequency

on (default) | off

Select to introduce phase noise as a function of frequency to the VCO. By default, this option is selected.

Phase noise frequency offset (Hz) — Frequency offsets of phase noise from carrier frequency

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

The frequency offsets of phase noise from the carrier frequency specified as a positive real valued vector in Hz.

Dependencies

To enable this parameter, select Add phase noise in the Impairments tab.

Programmatic Use

Block parameter: Foffset

Type: character vector

Values: positive real valued vector

Default: [30e3 100e3 1e6 3e6 10e6]

Data Types: double

Phase noise level (dBc/Hz) — Phase noise power at specified frequency offsets relative to the carrier

[-56 -106 -132 -143 -152] (default) | negative real valued vector

The phase noise power in a 1 Hz bandwidth centered at the specified frequency offsets relative to the carrier specified as a negative real valued vector in dBc/Hz. The elements of Phase noise level corresponds to relative elements in the Phase noise frequency offset.

Dependencies

To enable this parameter, select Add phase noise in the Impairments tab.

Programmatic Use

Block parameter: PhaseNoise

Type: character vector

Values: negative real valued vector

Default: [-56 -106 -132 -143 -152]

Data Types: double

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).

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.

More About

VCO Subsystem

The VCO subsystem block consists of two subsystems, Ideal VCO and Real VCO encapsulated under one variant subsystem.

If Add phase noise impairment is disabled, then the Ideal VCO subsystem gets active. This produces the following two orthogonal output signals, without any phase noise impairment and hence the name Ideal VCO:

$$\begin{array}{l}{y}_1(t)=A\cos {\displaystyle \int \left(2\pi K_{\text{vco}}*V_{\text{ctrl}}+2\pi F_{\text{out}}\right)}dt\\ y_2(t)=-A\sin {\displaystyle \int \left(2\pi K_{\text{vco}}*V_{\text{ctrl}}+2\pi F_{\text{out}}\right)}dt\end{array}$$

Out of the two orthogonal outputs, only the real part of the signal, y₁(t) is connected to the output port of VCO.

When the Add phase noise impairment is enabled, the Real VCO block becomes active which introduces phase noise as a function of frequency to the ideal VCO output. The subsystem consists of the Ideal VCO block whose output goes into Phase noise subsystem. The latter adds phase noise impairment to the input signal by utilizing a Phase Noise block from the Communications Toolbox™. The complex phase noise is separated into real and imaginary parts, which are multiplied with the real and imaginary parts of the output of the ideal VCO, respectively.

References

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