A Novel Implementation of Digital Phase Shifters

In digital systems, linear phase shift or delay of a signal waveform by an integer multiple of the sampling period is a simple process that can be implemented as a cascade of unit delays in the network. If, however, it is desired to delay the signal waveform by an amount not equal to an integer multiple of the sampling period, then the process is considerably more difficult. In this case, the signal must be interpolated to obtain new samples of its waveform at noninteger sample times. In this paper, we propose a novel implementation for achieving such noninteger delays. The theory is based on the application of the concepts of decimation and interpolation proposed by Schafer and Rabiner 1 and Crochiere and Ilabiner. 2 It is shown that the actual implementation of the phase shifter or interpolator can be achieved by means of a simple convolution. Applications in which such noninteger delays in the signal waveform are required often occur when digital systems must interface with analog systems. For example, in the cancellation of echoes, digital systems are often used to generate artificial echoes by means of a simulation of an echo model. These artificial echoes are then subtracted from the original analog signal to cancel its echo. For best cancellation, the digital simulated echo may have to be delayed by a noninteger multiple of the sampling period. 1497