Tektronix, Inc.

The Grass Valley Group, Inc.

Ajay K Luthra

Ganesh Rajan

Dean S Messing

Philip S Crosby

Yih-Chyun Jenq

Stanley C Edwards

Regis J Crinon

Peter M May

Ronald Alspaugh

A sampling rate converter for converting an input digital signal, such as D2 PAL, into an output digital signal, such as D1 PAL, has a pair of polyphase filters. The input digital signal is input in parallel to the two polyphase filters, with the phase selected by one of the filters being offset by one from that of the other. The outputs of the polyphase filters are input to a linear interpolator to produce the output digital signal. The resolution of the sampling rate conversion is a function of the number of phases N of the polyphase filters and the number of interpolation steps M of the interpolator.

Sampling rate conversion using polyphase filters with interpolation

An adaptive spatio-temporal compression/decompression algorithm for a video image uses a quadtree hierarchy to represent each frame of the image, the quadtree hierarchy including intermediary nodes and leaves. For each leaf a temporal bit is added indicative of whether a significant intensity change occurred between two frames of the video image. If the temporal bit indicates the significant intensity change occurred between frames, then a new intensity value also is added to that leaf. A decoder using a state machine extracts from the resulting compressed data stream a start address, a block size and the new intensity value for each leaf having the significant intensity change between frames to update a display memory with the new intensity value at each pixel within the area defined by the start address and block size.

Adaptive spatio-temporal compression/decompression of video image signals

A format converter for converting an input signal having a specified format to a digital signal of a pre-existing format, and for converting the digital signal back to the input signal automatically, loads an active data portion of the input signal into an input first-in/first-out (FIFO) buffer at a first data rate and reads the active data portion together with dummy filler samples from the FIFO at a second data rate as the digital signal. The number, location and/or values of the filler samples identify the specified format. In reverse the filler samples are stripped from the digital signal and the resulting active samples are loaded into an output FIFO at the second data rate. The stripped filler samples are used to determine the specified format of the original source of the data signal, and the active samples are read from the output FIFO at the first data rate in the specified format to reproduce the input signal.

Format converter architecture

The present invention provides a method of using long digital filters in the presence of round-off errors by prescaling each filter coefficient by a scaling factor. The prescaled coefficients are used to weight input data samples. The resulting weighted data values are then divided by the appropriate scaling factor and combined to produce an output data sample.

Using long distance filters in the presence of round-off errors

A technique for reducing the number of coefficients in a low ratio sampling rate converter divides each input sampling rate interval into a plurality of bins. For each bin a set of conversion coefficients is computed. So long as output data samples lie within the same bin, the same set of coefficients is applied. When the output data samples move to another bin, the set of coefficients applied is changed. Thus a finite set of coefficients are computed rather than computing an exact set for each output data sample.

Coefficient reduction in a low ratio sampling rate converter

A method of determining estimates of fiber loss and return signal power for an optical fiber from a return signal uses a polynomial fit with data samples representing the return signal. From the polynomial fit an estimated fiber loss value is determined. The estimated return signal power is computed using a function of the estimated fiber loss value.

Estimation of fiber loss and return signal power

A method of detecting a splice in an optical fiber in the presence of noise generates a nulling filter from a segment of a signal received from the optical filter by determining a set of coefficients having an initial '1' followed by p-1 '0' values and w.sub.i finite impulse response filter values, where p is a prediction interval greater than the width of an expected splice signature. The received signal is processed by the nulling filter to remove exponentials from the received signal, leaving an error signal containing noise and splice information. The resulting error signal is processed by a correlation filter to reduce the noise in the error signal. The output from the correlation filter results in a noise reduced error signal with the splice appearing as a noticeable dip in the waveform. The waveform is passed through a threshold detector to identify the splice when the dip exceeds a predetermined threshold.

Detection of splices in an optical fiber

Stored waveform records representative of respective repetitions of a repetitive signal are processed by reading a first waveform record from memory to form a reference signal. A second waveform record is read from memory to form a second signal, and the second signal is shifted in time in such a manner as to minimize the power of a difference signal, of which the instantaneous magnitude is representative of the difference in instantaneous magnitude between the reference signal and the time-shifted second signal. If the waveform records are identical but for jitter, and the power of the difference signal is brought to zero, this implies that the first waveform signal is synchronous with the processed second waveform signal, i.e., there is no jitter between the two signals. If waveform records resulting from the reference signal and the processed second signal are then averaged, the level of noise in the averaged record is reduced relative to the stored records and the averaged record is free of distortion due to jitter.

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Beaverton, OR, United States of America

Ajay K Luthra