vco in high frequency

Hi.When I use vco block in high frequency(GB),the output is not a sin wave?and it is triangular wave.How do I set up the VCO parameters to have sinusoidal output in the 2.4 GHz frequency? Thanx.

Answer 1

[Pragati]

The triangular waveform you see on the Scope is most likely not caused by an incorrect VCO frequency setting.

If you are using the Ring Oscillator VCO from Mixed-Signal Blockset, the native output is not an ideal sinusoidal waveform. The block generates a pulse-train/ring-oscillator style output whose frequency is controlled by the input voltage. As a result, simply increasing the frequency to 2.4 GHz does not automatically produce a sine wave output.

Another aspect to consider is simulation resolution. At 2.4 GHz, the oscillation period is only:

If the Scope receives only a few simulation points per cycle, it connects those points with straight lines, which can make the waveform appear triangular even if the underlying oscillator behavior is correct.

If your goal is specifically to obtain a sinusoidal VCO output, I recommend looking at the Mixed-Signal Blockset example:

Generate Sinusoidal Output from VCO - MATLAB & Simulink

This example explains how to modify the Ring Oscillator VCO by:

1. Computing the instantaneous frequency from the VCO half-period.
2. Converting the frequency to angular frequency.
3. Integrating the angular frequency to obtain phase.
4. Generating the sinusoidal waveform from the accumulated phase.