Timing error detector

Details Timing error detector Timing error detector

1989-09-11

1991-07-09

Safourek, Benedict V.

Pulse or digital communications

Repeaters

Testing

375106, 455260, H04L 2706, H04B 130

Patent

active

050311972

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The invention relates to a detector for use in synchronizing a clock pulse generated by a clock pulse generator in a receiver of synchronously transmitted data, which includes a pair of bandpass filters for respectfully receiving an in-phase component and a quadrature component of a demodulated received signal generated in the receiver from product of a received signal and an output signal of a carrier oscillator, harmonics of the in-phase and quadrature components being suppressed, and a combiner unit which is responsive to outputs signals of bandpass filters for generating a control signal to control the timing of the clock pulse generator.
Such timing error detectors (see FIGS. 1 and 2) are known, for example, from the articles cited below.
In connection with synchronous data transmission, it is important for the receiver to derive the precise sampling moment from the received data. For this purpose, a timing error detector TD (FIGS. 1, 2) generates by way of non-linear operations an output signal u.sub.T whose fundamental mode corresponds to the clock pulse frequency and whose zero passages permit the derivation of the sampling moment. The clock pulse oscillation is freed of interferences by means of narrowband filtering through a bandpass filter or a phase control loop (PLL).
If the transmission takes place in the carrier frequency domain, in addition to the clock pulse, the carrier frequency and carrier phase must also be synchronized in the receiver. This produces acquisition problems if the carrier frequency offset is great compared to the bandwidth of the carrier phase control loop. One possibility to synchronize the carrier phase control loop is to employ a frequency control loop in addition to the carrier phase control loop. In this connection reference is made to German Published Patent Application 3,707,762.
Thus, in addition to the carrier phase control loop for synchronization of the carrier phase, which will not be discussed in detail here, the receiver requires a frequency detector for the frequency control loop and a timing error detector TD for clock pulse control. Timing error detectors, for QPSK (quadrature phase shift keyed) signals are described in the article by Gardner entitled "A BPSK/QPSK Timing-Error Detector For Sampled Receivers", IEEE Com.-34, No. 5, May 1986, pages 423-429 (Reference 1) and in the article by Godard entitled "Passband Timing Recovery In All-Digital Modem Receiver," IEEE Com.-26, No. 5, May 1978, pages 517-523 (Reference 2).


SUMMARY OF THE INVENTION

It was the object of the invention to provide a timing error detector of the above-mentioned type which, without requiring much additional circuitry, can simultaneously be used as a frequency detector, with the detectors operating substantially independently of one another and furnishing output signals that are as free of jitter as possible.
The solution of this problem is to provide a second linkage circuit which generates from the complex output values of the bandpass filters a control signal to control the frequency of the carrier oscillator.
The detector circuit according to the invention has the following advantages: with little additional expense it can simultaneously be used as a frequency detector, with the additional circuitry expenditures resulting from the provision of a further linkage circuit (combiner unit) which generates the desired control signal. The two detectors operate substantially independently of one another and furnish output signals which are very poor in jitter. The acquisition time is greatly reduced by the detector circuit according to the invention.
With suitable pre-equalization before bandpass filtering, the jitter component in the phase detector as well as in the frequency detector can be reduced almost to zero. The independent operation of the two detectors resides in the fact that the frequency detector is independent of the timing error offset and the timing error detector is substantially independent of the frequency offset of the demodulated sign

REFERENCES:
patent: 3745255 (1973-07-01), Fletcher
patent: 4336500 (1982-06-01), Attwood
patent: 4419759 (1983-12-01), Poklemba
patent: 4538111 (1985-08-01), Giusto
patent: 4726043 (1988-02-01), Levesque
Proceedings of the IEEE; vol. 71, No. 6, Jun. 1983, pp. 754-766, "Frequency-Selective Scintillation Effects and Decision Feedback Equalization in High Data-Rate Satellite Links", Bogusch, Guigliano and Knepp.

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