Not getting desired signal when I multiply sine wave and pulse generator in Simulink

In Simulink, I am using the following model to multiply sine wave and pulse generator. And I am getting a triangular waveform enveloped in sine wave at the output.

Sine wave block parameters:

Sine type:Time based

Time(t): Use simulation time

Amplitude:5

Bias:0

Frequency (rad/sec): 2*pi*500

Phase (rad): pi/2

Sample time: 0

Pulse generator block parameters:

Pulse type: Time based

Time(t): Use simulation time

Amplitude:1

Period (secs): 0.0001

Pulse width (% of period): 50

Phase delay (secs): 0

The ouputs of Sine Wave Scope, Pulse Generator Scope and Product Scope are as follows:

Sine Wave Scope:

Pulse Generator Scope:

Product Scope:

Why the product output is triangular waveform enveloped in the sine wave?

Answer 1

[Paul]

Hi Deepankar,

If the question shows the full model, then we can see it has no continuous states. The solver will be VariableStepDiscrete (even if it's set to one of the ODE solvers, it stll reverts to discrete as far as I can tell, at least in 2024a). If the max step size for the solver is set to auto, it ends up with a constant step size of 5e-5, which is the pulse width. So the output of the pulse generator is 1-0-1-0-1-0 ... at the simulation step times, which results in the triangular shape in the scope. Set the max step size in the solver to be 1/10 or 1/100 of the pulse generator period, and you'll see the curvature of the sine wave in the time frames when the pulse is non-zero.