Generate variable frequency sinusoid
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:
Starting in R2016b, instead of using the
to perform the operation defined by the System object™, you can
call the object with arguments, as if it were a function. For example,
= step(obj,x) and
y = obj(x) perform
H = comm.DiscreteTimeVCO creates a discrete-time
voltage-controlled oscillator (VCO) System object,
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( 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 (
Amplitude of output signal
Specify the amplitude of the output signal as a double- or single-precision,
scalar value. The default is
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
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
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
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
|step||Generate variable frequency sinusoid|
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 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')
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
property in single-precision or double-precision. The block does not
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 *
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 *
Usage notes and limitations:
See System Objects in MATLAB Code Generation (MATLAB Coder).