Transmitter for the transmission of signals by pulse code modulation

Claim 1

A transmitter system comprising a pulse generator of periodic timing pulses, a pulse code modulator coupled to said pulse generator for providing two-valued output pulses in synchronism with said timing pulses, a first means for generating a first negative feedback signal for said pulse code modulator, said first means comprising a dynamic control generator coupled to the output of said pulse code modulator for providing dynamic control pulses in accordance with said two-valued output pulses, a first integrating network for integrating said dynamic control pulses to provide a dynamic control signal, and pulse modulating means coupled to the output of said pulse code modulator for modulating said two-valued output pulses in accordance with said dynamic control signal and producing modulated output pulses of either the one or the other polarity according to the value of said twovalued output pulses, a comparison system for providing a signal for controlling said pulse code modulator, said comparison system comprising a difference producer having at least a first input, a second input and an output, means to couple an analog input signal to said transmitter to said first difference producer input, and coupling means including a second integrating network, said coupling means coupling the output of said pulse modulating means to said second difference producer input and the output of said difference producer to said pulse code modulator, a second means for generating a second negative feedback signal for said pulse code modulator, said second means comprising a third integrating network, means to couple the output of said pulse code modulator to the second means, and means to couple the output of the second means to said comparison means, said second integrating network having a cut-off frequency of the same order of magnitude as the lowest frequency in said analog input signal, said third integrating network having a cut-off frequency which is at least one order of magnitude lower than the cut-off frequency of said second integrating network so that, at said lowest analog input signal frequency, the second feedback signal has substantially no influence on the pulse code modulator when said dynamic control signal has its lowest value, the influence of said second feedback signal on the pulse code modulator at substantially zero frequency being at least one order of magnitude greater than that of the first feedback signal when said dynamic control signal has its lowest value.