comm.DiscreteTimeVCO

Generate variable frequency sinusoid

Description

The comm.DiscreteTimeVCO System object™ object generates a signal whose frequency shift from the quiescent frequency property is proportional to the input signal, treating the input as a voltage.

To generate a variable frequency sinusoid:

1. Create the comm.DiscreteTimeVCO object and set its properties.

2. Call the object with arguments, as if it were a function.

To learn more about how System objects work, see What Are System Objects?

Creation

Syntax

discreteVCO = comm.DiscreteTimeVCO

discreteVCO = comm.DiscreteTimeVCO(Name=Value)

Description

discreteVCO = comm.DiscreteTimeVCO creates a discrete-time voltage-controlled oscillator (VCO) System object, discreteVCO. This object generates a sinusoidal signal, shifting its frequency from the specified quiescent frequency to a value proportional to the input signal.

discreteVCO = comm.DiscreteTimeVCO(Name=Value) sets properties using one or more optional name-value arguments. For example, comm.DiscreteTimeVCO(OutputAmplitude=2.5) sets the amplitude of the output signal to 2.5.

Properties

Unless otherwise indicated, properties are nontunable, which means you cannot change their values after calling the object. Objects lock when you call them, and the release function unlocks them.

If a property is tunable, you can change its value at any time.

For more information on changing property values, see System Design in MATLAB Using System Objects.

OutputAmplitude — Amplitude of output signal

1 (default) | scalar

Amplitude of the output signal, specified as a scalar.

Tunable: Yes

Data Types: single | double

QuiescentFrequency — Quiescent frequency of output signal

10 (default) | scalar

Quiescent frequency of the output signal in hertz, specified as a scalar. This quiescent frequency refers to the frequency of the output signal when the input value is zero.

Tunable: Yes

Data Types: single | double

Sensitivity — Sensitivity of frequency shift of output signal

1 (default) | scalar

Sensitivity of the frequency shift of the output signal to the input, specified as a scalar. This value scales the input voltage, leading to a corresponding shift in frequency from the specified quiescent frequency. Units are in hertz per volt.

Tunable: Yes

Data Types: single | double

InitialPhase — Initial phase of output signal in radians

0 (default) | scalar

Initial phase of the output signal in radians, specified as a scalar.

Data Types: single | double

SampleRate — Sample rate of input in hertz

100 (default) | positive scalar

Sample rate of the input in hertz, specified as a positive scalar

Data Types: single | double

Usage

Syntax

Y = discreteVCO(X)

Description

Y = discreteVCO(X) produces a sinusoidal signal, Y, shifting its frequency from the specified QuiescentFrequency property to a value that is proportional to the input signal, X.

Input Arguments

X — Input signal

scalar | column vector

Input signal, specified as a scalar or column vector.

Data Types: single | double

Output Arguments

Y — Output signal

scalar | column vector

Output signal, returned as a scalar or column vector. Y has the same data type and size as X.

Object Functions

To use an object function, specify the System object as the first input argument. For example, to release system resources of a System object named obj, use this syntax:

release(obj)

Common to All System Objects

step	Run System object algorithm
release	Release resources and allow changes to System object property values and input characteristics
reset	Reset internal states of System object

Examples

Generate FSK Signal Using Discrete Time VCO

Create a signal source System object™.

reader = dsp.SignalSource;

Generate random data and apply rectangular pulse shaping.

reader.Signal = randi([0 7],10,1);
reader.Signal = rectpulse(reader.Signal,100);

Create a signal logger and discrete time VCO System objects.

logger = dsp.SignalSink;
discreteVCO = comm.DiscreteTimeVCO( ...
    OutputAmplitude=8, ...
    QuiescentFrequency=1);

Generate an frequency shift keying (FSK) signal.

while(~isDone(reader))
    sig = reader();
    y = discreteVCO(sig);
    logger(y);
end
oscsig = logger.Buffer;

Plot the generated FSK signal.

t = (0:length(oscsig)-1)'/discreteVCO.SampleRate;
plot(t,reader.Signal,'--r', LineWidth=3)
hold on
plot(t,oscsig,"-b");
hold off
xlabel("Time (s)")
ylabel("Amplitude (V)")
legend("Input signal","FSK signal","location","se")

Algorithms

The comm.DiscreteTimeVCO system object generates a signal with a frequency shift from the quiescent frequency that is proportional to the input signal, interpreted as a voltage. Given the input signal (u(t)), the expression for the output signal becomes

$$y(t)=A_c\cos \left(2\pi f_{c}t+2\pi k_c{\displaystyle {\int }_0^{t}u(\tau )d\tau +\phi }\right)$$

where:

• A_c is the output amplitude.

• f_c is the quiescent frequency.

• k_c is the input sensitivity.

• $$\phi$$ is the initial phase.

Extended Capabilities

C/C++ Code Generation

Generate C and C++ code using MATLAB® Coder™.

Usage notes and limitations:

See System Objects in MATLAB Code Generation (MATLAB Coder).

Version History

Introduced in R2012a