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An analysis of a partially digitized phase-locked loop using -transform sampled data theory is presented. Responses are obtained at various junctions of the loop for both a step frequency input and for a sinusoidal frequency input. These responses are compared with the corresponding responses for an analog phaselocked loop. Stability criterion and root locus are determined. Effects of quantization are studied. It is concluded that over most of the range of operation the behavior of the digital phase-locked loop is nearly identical to the corresponding analog phase-locked loop, but that in addition, certain possible advantages may occur as a result of the digitization.