Circuitry for generating reference signal for delta encoding systems
AssigneeAnalog and Digital Systems, Inc.
InventorRichard E. DeFreitas
Life of this patent
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Abstract
In an electrical system of the type in which a digitally encoded signal is determined at least in part by the difference between a present value of an input signal and a reference signal representative of a past value of the input signal, improved circuitry for generating the reference signal. The improved circuitry comprises extraction means including a filter for extracting from the pattern of bits in the digitally encoded signal information relating to the time derivative of the present value of the input signal and an envelope detector for processing the output of the filter to provide a control signal, and integrating means responsive to the control signal to provide the reference signal.
Claims27
In an electrical system of the type in which a digitally encoded signal is determined at least in part by the difference between a present value of an input signal and a reference signal representative of a past value of said input signal, improved circuitry for generating said reference signal, comprising extraction means for extracting from the pattern of bits in said digitally encoded signal information relating to the time derivative of said present value to provide a corresponding control signal, said extraction means including a filter, and [an envelope detector] means for providing a control signal that rises, to follow increases in said derivative, and decays more slowly than it rises upon decreases in said derivative ,said control signal from said extractioon means being fed to a digital-signal-generating means, which comprises an integrating means, said integrating means being responsive to said [control] digitally encoded signal to provide said reference signal.
In an electrical system of the type in which a digitally encoded signal is determined at least in part by the difference between a present value of an input signal and a reference signal representative of a past value of said input signal, improved circuitry for generating said reference signal, comprising
- extraction means including a filter for extracting from the pattern of bits in said digitally encoded signal information relating to the time derivative of said present value to provide a corresponding control signal,
- integrating means responsive to said control signal to provide said reference signal,
- modulating means for feeding back to an input of said filter a modulated signal comprising said control signal modulated by said encoded signal, and
- means for providing as an input to said filter a mixture of said modulated signal and said digitally encoded signal, said mixture being selected to provide tracking at low slew rates between said input and the decoded output while maintaining dynamic range.
[27. The electrical system of claim 1 wherein said envelope detector includes means producing a rectified control signal that rises rapidly, to follow increases in the filter output, and decays more slowly
- than it rises upon decreases in the filter output.] 28. The system of claim [27] 1 wherein the speed of decay of said means [producing a rectified] for providing a control signal is determined by a hold time constant that is selected to be long enough
- to make quantization noise less audible. 29. The electrical system of claim 28 wherein said hold time constant is selected to be longer than the period of the lowest frequency of the input signal.
Dependencies are inferred from the claim text.