A NEW AFC CIRCUIT EMPLOYING DOUBLE-PRODUCT TYPE FREQUENCY-DISCRIMINATOR IN VERY-LOW CNR ENVIRONMENTS

This paper proposes a new AFC (automatic frequency control) circuit em ploying a double-product type frequency discriminator to enable fast a cquisition in very-low CNR (carrier to noise power ratio) environments . The frequency step responses of the proposed AFC circuit are theoret ically analyzed. In addition this paper evaluates the performance of t he proposed AFC circuit by computer simulation in very-low CNR environ ments. The simulation results confirm that click noise at the frequenc y discriminator causes large frequency tracking error and that this er ror can be improved by increasing the delay time of the double-product type frequency discriminator. The frequency error can be also reduced by introducing the proposed frequency discriminator to modify the fre quency error detection performance. The acquisition time of the propos ed AFC circuit can be reduced by about 100 symbols compared to the con ventional cross-product type AFC circuit.