Chirp (DSP Blockset)

Generate a swept-frequency cosine.

Library

DSP Sources

Description

The Chirp block outputs a unity-amplitude swept-frequency cosine (chirp) signal. The frequency trajectory of the output signal is defined by two instantaneous frequency values. The instantaneous output frequency is initialized to the Initial frequency parameter value at the start of the simulation, and then varies continuously to the Frequency at target time parameter value. The transition between these two frequencies takes place over the period of time specified in the Target time parameter.

The frequency trajectory established by these three parameters is maintained until the end of the simulation. That is, the frequency of the output (after the target time) continues to change according to the specified trajectory. Note that the output of this block is continuous.

The method that the block uses to transition between the specified instantaneous frequencies is set by the Frequency sweep parameter, and can be Linear, Quadratic, or Logarithmic:

Linear uses an instantaneous frequency sweep f_i(t) of

where f₀ is the Initial frequency parameter value, and

ensures that the desired Frequency at target time value, f₁, occurs at the specified Target time, t₁.

Quadratic uses an instantaneous frequency sweep f_i(t) of

where

Logarithmic uses an instantaneous frequency sweep f_i(t) of

where

For the logarithmic sweep, the Frequency at target time parameter value must be greater than the Initial frequency parameter value.

Dialog Box

Frequency sweep: Function defining the instantaneous frequency trajectory.
Initial frequency: Frequency of output cosine at t=0.
Target time: Time corresponding to the second defining frequency, specified by Frequency at target time.
Frequency at target time: Second frequency defining the sweep trajectory.
Initial phase: Phase of the cosine output at t=0.