page_title: Costas loop
section_title: Frequency acquisition
hierarchical_section_title: Costas loop / Frequency acquisition
caption_attribution_description: English: Block-scheme of Costas Loop during synchronization process (pull-in, unlocked state)
context_page_description: A Costas loop is a phase-locked loop based circuit which is used for carrier frequency recovery from suppressed-carrier modulation signals and phase modulation signals. It was invented by John P. Costas at General Electric in the 1950s. Its invention was described as having had "a profound effect on modern digital communications".
  The primary application of Costas loops is in wireless receivers. Its advantage over other PLL-based detectors is that at small deviations the Costas loop error voltage is as compared to. This translates to double the sensitivity and also makes the Costas loop uniquely suited for tracking Doppler-shifted carriers especially in OFDM and GPS receivers.
context_section_description: The classical Costas loop will work towards making the phase difference between the carrier and the VCO become a small, ideally zero, value. The small phase difference implies that frequency lock has been achieved.
caption: Costas loop before synchronization
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