Digital data receiver with automatic timing recovery and control

Abstract

A data transmission system is provided with a double sideband suppressed carrier transmitter and receiver for transferring data between data processing apparatuses. The transmitter and receiver communicate over a telephone line which has physical characteristics which produce delay and attenuation distortion and phase jitter in the transmitted signal. The receiver includes a sampler for converting the transmitted signal into a digital signal, an automatic equalization network for correcting the delay and attenuation distortion, and a phase correction network compensating for frequency offset, phase offset, and phase jitter. The phase corrected and equalized signal is then detected and introduced to the data processing apparatus. An error signal calculator is responsive to the phase corrected signal and the detected signal to provide a system error signal for automatically updating the functions of the equalization and phase correction networks in accordance with the characteristics of the incoming signal. A timing control network which is also responsive to the system error signal, provides a timing error signal for correcting the sampling rate of the sampler. Filters in the transmitter and receiver provide the system with partial response signaling so the bandwidth of the system can be minimized, and even telephone lines of poor quality can accommodate a full duplex secondary channel for system control.