Communications Blockset

Fractional-N Frequency Synthesis Demo

This example shows how to simulate a phase-locked fractional-N frequency synthesizer. The model multiplies the frequency, Fr, of a reference signal by a constant n+m, to produce a synthesized signal of frequency Fr*(n+m). A feedback loop maintains the frequency of the synthesized signal at this level.

This example is similar to the Fractional-N Frequency Synthesis Demo, which produces a synthesized signal of frequency fr*N/M, where N and M are integers. In this example, n is an integer and m is a fraction between 0 and 1. There are several advantages to this approach, since it enables you to approximate the frequency of the synthesized signal with relatively small values for n and m. It also enables you to use a larger reference frequency. See the Reference for more information.

To open the model, type fracsyn_sim at the MATLAB prompt (or click here if you are reading this in the MATLAB Help browser). In addition to the model window, shown below, this opens two Scope windows, labelled "Control Signal" and "Synthesized Signal."

Simulation Parameters

Variables in the Model