Coded data generation or conversion – Converter compensation
Reexamination Certificate
1998-10-13
2001-04-10
Williams, Howard L. (Department: 2819)
Coded data generation or conversion
Converter compensation
C341S122000
Reexamination Certificate
active
06215427
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to an analog-digital conversion device, especially adapted to the reception of signals transmitted by cable.
The basis of the invention has consisted in developing a conversion device suitable for the analog-digital conversion of a 256 QAM modulated signal within the frequency spectrum from 3.2 to 11.2 MHz and with a peak-to-peak dynamic swing of 1 volt, the input signal being applied via a capacitive coupling.
The capacitive coupling causes the loss of the continuous component of the input signal. The device will therefore have to take this into account. On the other hand, the dynamic swing of the signal is just 1 volt peak-to-peak, which is not much. This problem will also have to be taken into account. Lastly, an attempt will be made to minimize certain forms of noise.
SUMMARY OF THE INVENTION
The subject of the invention is a device for the analog-digital conversion of an input signal, characterized in that it comprises:
means for transposing the input signal into two differential signals;
means for restoring a continuous component of each of the differential signals at the mid-voltage of the conversion range of an analog-digital converter;
at least one differential comparator whose output is linked to the input of the analog-digital converter and whose two differential inputs respectively receive one of the two differential signals.
By employing at least one differential comparator it is possible on the one hand to double the dynamic swing of the signal, the two differential signals having opposite excursions with respect to a restored continuous component, and on the other hand to overcome the common-mode noise.
The function of the means for restoring the continuous component is to centre the continuous component on the mid-voltage of the conversion range of the converter, so as to limit the saturation of the converter.
According to a particular embodiment, the means for restoring a continuous component comprise in series a low-pass filter intended to filter the digital word output by the converter and a switched current source intended to charge or discharge a storage capacitor as a function of the most significant bit at the output of the filter.
According to a particular embodiment, the means for transposing the input signal to a first of the two differential signals comprise a subtracter and an adder which are intended to add the input signal to twice the mid-voltage of the conversion range of the converter and to subtract therefrom the restored continuous component.
According to a particular embodiment, the means for transposing the input signal to a second of the two differential signals comprise a subtracter and an adder which are intended to subtract the input signal from the restored continuous component.
According to a particular embodiment, the device furthermore comprises amplifiers used as buffers respectively for the input voltage, the mid-voltage of the reference range of the converter and the restored continuous component.
Other characteristics of the invention will emerge via the description of a particular non-limiting illustrative embodiment depicted by the accompanying figures.
REFERENCES:
patent: 4571507 (1986-02-01), Collings
patent: 4602374 (1986-07-01), Nakamura et al.
patent: 4633223 (1986-12-01), Senderowicz
patent: 4875049 (1989-10-01), Yoshida
patent: 388 130 A2 (1990-09-01), None
patent: 91/15899 (1991-10-01), None
Bonhoure Bruno
Palllardet Frédéric
Rouzier Thierry
Hermann Eric P.
Kurdyla Ronald H.
Thomson Multimedia
Tripoli Joseph S.
Williams Howard L.
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