a digital loop filter in the carrier - recovery loop of a digital communications receiver . the recovery loop is a pll that keeps the receiver oscillator locked to the carrier wave , and the loop filter provides control over the pll &# 39 ; s frequency response by conditioning an error signal that is fed back to the receiver oscillator . in the present invention , the error signal is a digital signal , and the loop filter is implemented in digital hardware . with this implementation the characteristics of the loop filter are determined by logic design rather than by physical features of analog components , thereby giving this filter a more precise function than one with analog integrators . this implementation is also immune to the low tolerances typical of the manufacturing process for analog devices , and is more easily adjusted than its analog counterparts . two gain coefficients characterize the loop filter in the present invention . these gain coefficients are chosen to be powers of two , simplifying the process of multiplying them with the digital error signal . the gain coefficients are read from a memory , making the loop filter easily programmable . by changing the gain coefficients during operation of the receiver , the carrier - recovery loop can be placed in one of the several operating modes , including acquisition , tracking , and hold . the receiver can be configured with the appropriate values of the gain coefficients for each operating mode during the initial assembly and during subsequent reconfigurations .