Just as the half-band decimator is an optimized version of the more general polyphase decimation filter, the half-band interpolator is a special case of a polyphase interpolator. The following figure shows the half-band interpolator.
The coefficient set for a true half-band interpolator is identical to that of a half-band decimator with the same specifications. The large number of zero entries in the impulse response is exploited in exactly the same manner as with the half-band decimator to produce hardware-optimized half-band interpolators. The process is presented in the following figure. The following figure (a) is the impulse response, the following figure (b) shows the polyphase partition, and the following figure (c) is the optimized architecture that has taken full advantage of the 0 entries in the coefficient data, along with coefficient symmetry.
The high density of zero-valued filter coefficients is exploited in the FPGA realization to produce a minimal area implementation.
