Abstract: The applique rate converter permits a digital multiplexer to support any data rate less than half of its input port design rate. The applique rate converter develops a composite data stream consisting of alternate data bits and data boundary bits. The data boundary bits change state at each new data bit (corresponding to a change in the data clock.) The composite bit stream is increased to the output data rate by means of a circuit called the `synchronizer`. At the demultiplex side of the applique, the data is separated from the composite stream by a decoding process and, if necessary, the data stream is rate smoothed. The major sections of the applique rate converter are the `synchronizer` at the multiplex side and the data separator and rate smoothing circuits at the demultiplex side.