PLL Carrier Tracking

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Implements a Phase Locked Loop (PLL) which locks to the carrier of the input frequency and outputs the input signal mixed with that carrier.

This PLL locks onto a [possibly noisy] reference carrier on the input and outputs that signal, downconverted to DC.


  • Important: The frequency parameters below are in radians per sample rather than Hz.
radians per sample = 2 * pi * freq / sample rate
  • for example:
    • input centered at 0 Hz.
    • Sample rate = 48kHz.
    • frequency variations to track +- 500Hz.
    • Max freq = 0.0654
    • Min freq = -0.0654
  • If the input signal were to be at 10kHz, then the Max freq would be 1.374 and the Min freq would be 1.246
  • This block seems to require an input signal of at least -30db in order to lock to the carrier.


(R): Run-time adjustable

Loop bandwidth (R)
The loop bandwidth determines the lock range and should be set in the range of pi/200 to 2pi/100 (0.0157 to 0.0628).
Max freq
Maximum frequency of the carrier in radians per sample. See Notes above.
Min freq
Minimum frequency of the carrier in radians per sample. See Notes above.

Example Flowgraph[edit]

This flowgraph shows the use of a PLL Carrier Tracking block in an AM receiver.

Complex to Mag.png

Source Files[edit]

C++ files
Header files
Public header files
Block definition