This paper proposes a concept of all phase data space

and based on the DFT/IDFT filtering brings about a new type of zero-phase filter

the all phase DFT (APDFT) digital filter.The paper gives the transform and inverse transform between its impulse response and corresponding DFT response vector

demonstrates some important properties of this filter.The APDFT method is a new scheme for FIR filter design

possessing concurrently the merits of the windowing and the frequency sampling method.It has the advantage of the conventional methods in overall filter characteristics that have been verified by theoretical analysis and simulation experiments.The APDFT digital filter can be implemented with common convolution structure

and a direct frequency domain network as well.This paper gives the architecture of the network and an associate simplified algorithm.This network has real-time self-design function.It can constitute a time-variant system applied to the occasion that requires filter's transfer function variable in real-time

can be easily integrated into a universal zero-phase digital filter with all of its length and frequency response programmable

and can be used to realize sub-band filtering with strictly complementary.