vco

Signal Processing Toolbox

Voltage controlled oscillator.

y = vco(x,Fc,Fs)
y = vco(x,[Fmin Fmax],Fs)

Description

y = vco(x,Fc,Fs)

creates a signal that oscillates at a frequency determined by the real input vector or array x with sampling frequency Fs. Fc is the carrier or reference frequency; when x is 0, y is an Fc Hz cosine with amplitude 1 sampled at Fs Hz. x ranges from -1 to 1, where -1 corresponds to a 0 frequency output, 0 to Fc, and 1 to 2*Fc. y is the same size as x.

y = vco(x,[Fmin Fmax],Fs)

scales the frequency modulation range so that -1 and 1 values of x yield oscillations of Fmin Hz and Fmax Hz respectively. For best results, Fmin and Fmax should be in the range 0 to Fs/2.

By default, Fs is 1 and Fc is Fs/4.

If x is a matrix, vco produces a matrix whose columns oscillate according to the columns of x.

Example

Generate two seconds of a signal sampled at 10,000 samples/second whose instantaneous frequency is a triangle function of time:

Fs = 10000;
t = 0:1/Fs:2;
x = vco(sawtooth(2*pi*t,0.75),[.1 0.4]*Fs,Fs);

Plot the spectrogram of the generated signal.

specgram(x,512,Fs,kaiser(256,5),220)

Algorithm

vco performs FM modulation using the modulate function.

Diagnostics

If any values of x lie outside [-1,1], vco gives the following error message:

X outside of range [-1,1].

`demod`	Demodulation for communications simulation.
`modulate`	Modulation for communications simulation.