Transmitter for transmitting a shape-controlled signal over a communication line

摘要

A transmitter (4) for a controlled-shape switched signal on a communication line (1) comprises a signal generator including a capacitor (19) and a feedback loop responsive to a voltage across the capacitor (19) and to an input signal (TX) for supplying a shaped current (IS) for charging the capacitor (19) so as to define an edge of the switched signal. Signal producing means (9, 21) in the signal generator is responsive to the capacitor voltage for applying the controlled-shape switched signal to the line. The signal generator includes an amplifier (49) having an input terminal and an output terminal across which the capacitor means (19) is connected and at which it generates an amplifier output voltage (VO). <??>The feedback loop is arranged to maintain a minimum value of the shaped current (IS) at least in steady state conditions of the input signal (TX). The signal generator comprises first and second current diversion means (52, 53) operative at least in the steady state conditions in response to relative magnitudes of the amplifier output voltage (VO) and first and second limit voltages respectively for controlling supply of charging current (Ic) to the amplifier and the capacitor (19) so as to tend to reduce charging and discharging of the capacitor means (19) in the steady state conditions and to maintain a steady state magnitude of the amplifier output voltage (VO) even against fluctuations induced by electromagnetic perturbations on the communication line. <IMAGE>