Direct conversion radio receiving system using digital signal processing for channel filtering and down conversion to base band

Abstract

A radio receiving system includes an orthogonally-modulated waveform detection/channel filter section an I signal root Nyquist filter a Q signal root Nyquist filter and a signal detection/demodulation section The orthogonally-modulated waveform detection/channel filter section further includes a first filter (a band pass filter) which permits passage of only a signal at a frequency band assigned to a communications system from which the radio receiving system receives a signal; a sample-and-hold circuit a Hilbert transformer a first channel filter through N-th channel filter and a clock signal shaping/controlling section The band pass filter is provided with the characteristics which cancel the aperture effect due to a sampling operation, thus compensating for the aperture effect due to a sampling operation.