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comm.DiscreteTimeVCO System object

Package: comm

Generate variable frequency sinusoid

Description

The DiscreteTimeVCO (voltage-controlled oscillator) object generates a signal whose frequency shift from the quiescent frequency property is proportional to the input signal. The input signal is interpreted as a voltage.

To generate a variable frequency sinusoid:

  1. Define and set up your discrete time voltage-controlled oscillator object. See Construction .

  2. Call step to generate a variable frequency sinusoid according to the properties of comm.DiscreteTimeVCO. The behavior of step is specific to each object in the toolbox.

Construction

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

H = comm.DiscreteTimeVCO(Name,Value) creates a discrete-time VCO object, H, with each specified property set to the specified value. You can specify additional name-value pair arguments in any order as (Name1,Value1,...,NameN,ValueN).

Properties

OutputAmplitude

Amplitude of output signal

Specify the amplitude of the output signal as a double- or single-precision, scalar value. The default is 1. This property is tunable.

QuiescentFrequency

Frequency of output signal when input is zero

Specify the quiescent frequency of the output signal in Hertz, as a double- or single-precision, real, scalar value. The default is 10. This property is tunable.

Sensitivity

Sensitivity of frequency shift of output signal

Specify the sensitivity of the output signal frequency shift to the input as a double- or single-precision, real, scalar value. The default is 1. This value scales the input voltage and, consequently, the shift from the quiescent frequency value. The property measures Sensitivity in Hertz per volt. This property is tunable.

InitialPhase

Initial phase of output signal

Specify the initial phase of the output signal, in radians, as a double or single precision, real, scalar value. The default is 0.

SampleRate

Sample rate of input

Specify the sample rate of the input, in Hertz, as a double- or single-precision, positive, scalar value. The default is 100.

Methods

cloneCreate discrete-time VCO object with same property values
getNumInputsNumber of expected inputs to step method
getNumOutputsNumber of outputs from step method
isLockedLocked status for input attributes and nontunable properties
releaseAllow property value and input characteristics changes
resetReset states of discrete-time VCO object
stepGenerate variable frequency sinusoid

Examples

Generate an FSK signal using a discrete time VCO.

    % Create a SignalSource System object and generate random data
    hreader = dsp.SignalSource;
    hreader.Signal = randi([0 7],10,1);
    % Rectangular pulse shaping
    hreader.Signal = rectpulse(hreader.Signal, 100);
    % Create a signal logger System object
    hlogger = dsp.SignalSink; 
    % Create a discrete time VCO object and generate an FSK signal
    hdvco = comm.DiscreteTimeVCO('OutputAmplitude',8, ...
                                 'QuiescentFrequency',1);
    while(~isDone(hreader))
      sig = step(hreader);
      y = step(hdvco,sig);
      step(hlogger,y);
    end
    oscsig = hlogger.Buffer;
    % Plot FSK signal
    t = [0:length(oscsig)-1]'/hdvco.SampleRate;
    plot(t,hreader.Signal,'--r', 'LineWidth',3); hold on;
    plot(t,oscsig,'-b'); hold off;
    xlabel('time (s)');
    legend('Input Signal', 'FSK Signal');

Algorithms

This object implements the algorithm, inputs, and outputs as described on the Discrete-Time VCO block reference page. However, this object and the corresponding block may not generate the exact same outputs for single-precision inputs or property values due to the following differences in casting strategies and arithmetic precision issues:

  • The block always casts the result of intermediate mathematical operations to the input data type. The object does not cast intermediate results and MATLAB decides the data type. The object casts the final output to the input data type.

  • You can specify the SampleRate object property in single-precision or double-precision. The block does not allow this.

  • In arithmetic operations with more than two operands with mixed data types, the result may differ depending on the order of operation. Thus, the following calculation may also contribute to the difference in the output of the block and the object:

    input * sensitivity * sampleTime

  • The block performs this calculation from left to right. However, since sensitivity * sampleTime is a one-time calculation, the object calculates this in the following manner:

    input * (sensitivity * sampleTime)

See Also

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