Digital simulation of discrimination of characters in the noise-free case using only phase information of the Fourier transform is realized. This method maximizes the spectral bandwidth of the transfer function of the optical correlator. As a consequence, the discrimination capability is enhanced and the autocorrelation signal is the diffraction limited delta function. The results of discrimination are compared with the results obtained by another phase-only method, tandem component filter method, which also transforms an object function into diffraction limited delta function in the output plane with 100% light efficiency.