Coded data generation or conversion – Analog to or from digital conversion – Analog to digital conversion
Patent
1987-12-02
1989-07-25
Roskoski, Bernard
Coded data generation or conversion
Analog to or from digital conversion
Analog to digital conversion
H03M 134
Patent
active
048518468
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to an apparatus for converting an analogue, balanced signal to a digital signal by charge redistribution in a plurality of capacitive elements, which are each connected in series with a controllable switch with which a first terminal in each capacitive element, at least during an approximating phase, may be selectively connected to a first or a second reference voltage.
BACKGROUND ART
Balanced signals are usually utilized in telephony technology, these signals being distinguished by the voltages in both conductors in a conductor pair being equally as great but of opposing polarity. In analogue-digital conversion of a balanced signal it is known first to convert it to an unbalanced signal and thereafter to convert the unbalanced signal to a digital signal. In the balance-unbalance conversion, half the dynamic range is lost however, since the signal voltage is limited by the feed voltage. The useful signals will also be distorted during the conversion, due to lack of linearity in the balance-unbalance converter.
It is therefore desirable to enable the analogue-digital-conversion of a balanced signal without first converting it to an unbalanced signal. One method for this is to utilize a separate A/D converter for each of the signal conductors of the balanced signal, and to connect the A/D converter outputs to a digital difference former. An apparatus for carrying out this method will be relatively voluminous and expensive, however.
SUMMARY OF INVENTION
The object of the present invention is to provide an apparatus for the analogue-digital conversion of balanced signals, which is more reliable, less voluminous and cheaper than previously available apparatus. This object is achieved in an apparatus of the kind given in the introduction by utilizing two sets of capacitive elements, these sets being connected to their respective input on a single comparator. The comparator output signal controls a means for sampling and approximating logic, which generates control signals to the switches connected in series with the capacitive elements.
In accordance with the present invention, there is provided apparatus for converting an analogue, balanced signal to a digital signal by charge redistribution in a plurality of capacitive elements, each of the plurality of capacitive elements being connected in series with respective ones of a plurality of controllable switches with which a first terminal in each capacitive element, at least during an approximating phase, may be selectively connected to a first or a second reference voltage, characterized in that the plurality of capacitive elements are grouped in two sets comprising equally as many capacitive elements selected such that each capacitive element in a first set corresponds to a capacitive element with just as great a capacity in the second set, in that the capacitive elements and associated switches in the first set are arranged to act on a potential at a first point and in that corresponding capacitive elements and switches in the second set are arranged to act on a potential at a second point, in that a comparator is arranged for comparison of the potentials at said first and second points and in that means for sampling and approximating logic are arranged to generate a digital word which is changed during the approximating phase in response to the comparison of the comparator, said digital word being utilized for controlling said plurality of switches and that at an end of the approximating phase said word constitutes a digital output signal of the apparatus.
The characterizing features of the invention are disclosed in the claims.
BRIEF DESCRIPTION OF DRAWINGS
The invention will now be described in detail with reference to the drawings, in which
FIG. 1 illustrates an already known analogue-digital converter, and
FIGS. 2-4 illustrate first, second and third embodiments of an apparatus in accordance with the invention.
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 illustrates an A/D converter which is arranged
REFERENCES:
patent: 3056085 (1962-09-01), James
patent: 3140481 (1964-07-01), Hoffman
patent: 4195282 (1980-03-01), Cameron
patent: 4380756 (1983-04-01), Worsman
patent: 4661802 (1987-04-01), Yukawa
J. L. McCreary et al, "All-MOS Charge Redistribution Analog-to-Digital Conversion Techniques-Part 1", IEEE Journal of Solid-State Circuits, vol. SC-10, No., 6 (Dec. 1975), pp. 371-385.
Roskoski Bernard
Telefonaktiebolaget L M Ericsson
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