In order to calculate a slice level that enables to binarize a video signal into a prosper value, an amplitude evaluation value setting method is used to enable the selection of an optimum value that is appropriate to the shape of the digital signal.

Data slicer, data slicing method, and amplitude evaluation value setting method

An auxiliary video data slicer for extracting auxiliary video information from a video signal includes a peak detector. The peak detector determines a peak amplitude of horizontal sync pulses that are included in the video signal and a peak amplitude of a run-in-clock (RIC) waveform that is included in an auxiliary information component of the video signal. A variable threshold level for the peak detector is varied in a first range to detect the peak amplitude of the sync pulses. A threshold voltage for detecting the leading edge of sync pulses is derived from the peak amplitude of the sync pulses. The location of the RIC waveform within a video line interval is determined in response to detection of a sync pulse edge. The variable threshold level of the peak detector is varied in a second range to detect the peak amplitude of the RIC signal. A data slicing threshold level for extracting auxiliary video information is derived from the peak value of the RIC signal.

Auxiliary video data slicer with multi-mode peak detection for determining sync and data slicing levels

An isomorphism is derived between a typical bandpass broadcast television system to be used in transmitting teletext data and its complex baseband equivalent representation for use in analysis and computer simulations. The distortions introduced by a multipath channel are discussed. The complex noise process is modeled by a mixture of Gaussian and impulsive noise, and the parameters of the noise model are derived. The video signal-to-noise ratio SNR TV is related to other parameters such as the input noise variance, output noise power, and the carrier-to-noise density ratio. A complete simulation model for broadcast television transmission and reception is shown in block diagram form. The remaining components of the computer simulation model are briefly discussed and references given. These include topics such as amplitude control, computer generation of ensembles of complex impulse responses, simulation of synchronous, quasi-synchronous and envelope detectors, bit slicers, bit synchronizers, error-correcting codes, estimation of error statistics and bit error rates, and adaptive equalization. Validation is also briefly noted with references. Several examples of simulation results are given. Some of the implementation details, simulation results, and a flow diagram of the simulation program are provided. This teletext computer simulation model appears to be the most complete one created to this time and has been used extensively in performance analyses to evaluate new designs and gain insights into design improvements.

Modeling Broadcast Teletext Systems for Analysis and Computer Simulation Studies

The theoretical and practical engineering constraints, considerations, and methods for pulse shape design for North American broadcast teletext transmissions are described. The principles and concepts described are for broadcast over-the-air transmission, but they are also applicable to satellite and cable transmission of broadcast teletext signals. Overall objectives of pulse shape design are summarized. Basic constraints and considerations from the Nyquist theory are described. The practical and engineering constraints on teletext pulse shapes are discussed in detail. Pulse shape apportioning and specification are treated. A critical review is provided of the theory and design methods for teletext pulse shaping. A review of analytical and numerical approaches is given. Modelling and simulation approaches are described, including novel comprehensive model. Improved overall and transmitted pulse shapes are evaluated and their performance compared to that obtained with other common pulse shapes. >

http://ieeexplore.ieee.org/iel1/11/705/00018764.pdf

Theory and methods for design of pulse shapes for broadcast teletext

A regenerated data signal generation circuit includes a receiving circuit, first and second binarization circuits and a signal preparation circuit The receiving circuit receives a modulated signal and demodulates the modulated signal The first binarization circuit receives the demodulated signal and binarizes the demodulated signal while compensates for offset deviation of the demodulated signal by a first method as to output a first binarization signal The second binarization circuit receives the demodulated signal and binarizes the demodulated signal while compensates for offset deviation of the demodulated signal by a second method that is different from the first method so as to output a second binarization signal The signal preparation receives the first and second binaraization signals and selectively outputs a regenerated data signal prepared from one of the binarization signals

Regenerated data signal generation apparatus

It is shown that multipath propagation imposes a serious performance degradation on broadcast teletext systems designed according to the North American Basic Teletext Specifications. By using both analysis and a comprehensive computer simulation model of the teletext broadcast system, it was found that very significant gains in performance could be obtained by improving slicing level and clock synchronization circuit designs. Several slicing level and clock synchronization (also called bit timing recovery (BTR)) circuits were modeled and simulated and their performances compared. These included peak detecting, averaging, modified averaging, adaptive and ideal slicers. The averaging and adaptive slicers used with the correlator BTR circuit were found to give the best performance, but the complexity and cost of an adaptive slicer reduce the advantages of system implementation. >

Comparisons and improvements of designs of data slicers and clock synchronization circuits for broadcast teletext decoders operating in a multipath environment

R.M. Armstrong

Papers

Comparisons and improvements of designs of data slicers and clock synchronization circuits for broadcast teletext decoders operating in a multipath environment