| 摘要 |
PURPOSE:To cut off sound signals by obtaining precise muting action signals by detecting the receiving conditions in 4 phase DPSK demodulation circuit, in the voice digital stransmitter using carriers. CONSTITUTION:The 4 phase DPSK signals from an input terminal 16 are inputted in a demodulation circuit 18, also in a carrier regenerative circuit 41, and two kinds of carriers with a phase of pi/62 or -pi/2 will generate. After these carriers are multiplied with input signals by multiplying machines 34, 37, carrier components are removed by filters 35, 38 changed into 2-value signals, and digital signals are regenerated. The digital signals are restored to voice signals by a D/A conversion circuit via a decoder 19, and inputted via muting switches 30 to 33. The signals outputted from the low-pass filter 38 are identified in amplitude by an amplitude discrimination circuit 43, the signals outputted through an integrator 44 represent changes in demodulation signals amplitude generated by phase distortion. Under this condition, errors occur and therefore the muting switches 30 to 33 are turned off because of making a big noise. |
