Carrier Recovery Applications and Acquisition
Daniel B. Talbot · 2012
Frequency-multiplier carrier recovery is almost always followed by a PLL or in some cases by a narrow bandpass filter to improve SNR. The advantage of the Costas PLL is that it incorporates implicit carrier recovery and filtering. For carrier recovery SNR, it can be shown mathematically that the SNR for a frequency-multiply filter-divide approach is equal to the SNR of the Costas PLL approach assuming equal inertia (equivalent filtering). A frequency-squaring circuit may also prove a beneficial replacement for the Costas PLL, provided it is implemented open loop and then followed by a PLL to narrow-band its output spectrum and jitter. Hard limiting restores constant envelope behavior but the incidental phase modulation (ICPM) remains. But since such a radical improvement (reduction) in sidebands is realized using hard limiting, we can more easily distinguish false lock. Controlled Vocabulary Terms Band-pass filters; jitter; phase locked loops; phase modulation