Abstract: An apparatus receives a reference clock signal that is then applied to a first one of a number of series-connected controllable delay stages. The output of each delay stage is a further delayed version of its input, the amount of delay being controlled by a control signal. A phase relation between a first preselected one of the plurality of delayed reference clock signals and a second preselected one of the plurality of delayed reference clock signals is measured. Alternatively, it may be a phase relation between the reference clock signal and a preselected one of the plurality of delayed reference clock signals that is measured. The measured phase relation is compared with a desired phase relation, and the difference is an error signal that is fed back to the delay stages for use as the delay control signal. In this manner, the delayed reference clock outputs from the delay stages lock in to a very stable desired phase relation with respect to one another.

Abstract: A digitally compensated direct-conversion receiver includes devices for generating digital samples of a base-band in-phase signal and a base-band quadrature signal and for detecting the presence of a second-order product signal produced by an amplitude-modulated interfering signal. Also, the apparatus comprises a device for digitally compensating the digital samples by removing the second-order product signal, thereby producing compensated digital samples. In one method of digitally compensating samples of an information signal quadrature-modulating a carrier signal, estimated samples of a second-order product from a switched carrier signal are formed by averaging the digital samples during two time periods and by determining a time of ramps in the in-phase and quadrature signals that occur between the time periods due to the interfering signal. The digital samples may be differentiated and the results smoothed in determining the time of the ramps.