Baseband data switching apparatus for digital communications system

DETAILED DESCRIPTION An object of the present invention is to provide a baseband switching apparatus which facilitates synchronization of time lags and polarities and switching over of the regular standby channel without any data hit.
According to the present invention, there is provided a baseband data switching apparatus for switching a first and a second channels, each channel having means for receiving baseband unipolar data and clock recovering means for recovering a clock from said baseband unipolar data, the switching apparatus comprising: first and second data phase adjusting means (301-303, 305) respectively connected to the outputs of each of the data demodulating means in the first and second channels for respectively adjusting the phases of the baseband unipolar data in each channel in synchronism with the respective recovered clock; first and second clock phase adjusting means (304) respectively connected to the outputs of each of the clock recovering means for respectively adjusting the phases of the recovered clocks; first (106) and second (206) unipolar/bipolar conversion means respectively connected to the first and second phase adjusting means and to said first and second clock phase adjusting means for respectively converting the phase-adjusted baseband unipolar data into bipolar data in response to first and second control signals; first (104) and second (204) frequency divider means respectively connected to the first and second clock phase adjusting means for respectively dividing the frequencies of the phase adjusted and recovered clocks; first (105) and second (205) control signal supply means for respectively reversing the polarities of the outputs of the first and second frequency divider means in response to third (f) and fourth (f') control signals to provide the first and second control signals; coincidence detecting means for detecting coincidence or non-coincidence between the outputs from said first and second unipolar signal means; and means for selectively switching between the outputs of the first and second unipolar/bipolar conversion means