U.S. patent application number 09/473268 was filed with the patent office on 2002-08-01 for method and device of information transfer between circuits that exchange data via converters.
Invention is credited to COMBE, MICHEL, FRAISSE, CHRISTIAN.
Application Number | 20020101370 09/473268 |
Document ID | / |
Family ID | 9506842 |
Filed Date | 2002-08-01 |
United States Patent
Application |
20020101370 |
Kind Code |
A1 |
COMBE, MICHEL ; et
al. |
August 1, 2002 |
METHOD AND DEVICE OF INFORMATION TRANSFER BETWEEN CIRCUITS THAT
EXCHANGE DATA VIA CONVERTERS
Abstract
The present invention relates to a method and a device of
information transfer between two circuits exchanging data via
delta-sigma converters. The present invention includes coding the
information in the form of at least one signal of determined
frequency corresponding to an integer multiple of a frequency of
the digital data samples; mixing, at a first end of a line carrying
an oversampled digital signal of the converter, the signal of
determined frequency; extracting from the mixture, at a second end
of the line, the signal of determined frequency; and decoding the
corresponding information.
Inventors: |
COMBE, MICHEL; (MEYLAN,
FR) ; FRAISSE, CHRISTIAN; (GRENOBLE, FR) |
Correspondence
Address: |
JAMES H MORRIS
WOLF GREENFIELD & SACKS P C
FEDERAL RESERVE PLAZA
600 ATLANTIC AVENUE
BOSTON
MA
022102211
|
Family ID: |
9506842 |
Appl. No.: |
09/473268 |
Filed: |
December 27, 1999 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09473268 |
Dec 27, 1999 |
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09073495 |
May 6, 1998 |
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6031475 |
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Current U.S.
Class: |
341/143 |
Current CPC
Class: |
H04B 14/062
20130101 |
Class at
Publication: |
341/143 |
International
Class: |
H03M 003/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 7, 1997 |
FR |
97/05867 |
Claims
What is claimed is:
1. A method of information transfer between two circuits exchanging
data via delta-sigma converters, the method comprising the steps
of: coding the information in the form of at least one signal of
determined frequency corresponding to an integer multiple of a
frequency of digital data samples; mixing, at a first end of a line
carrying an oversampled digital signal of the converter, said
signal of determined frequency; extracting from the mixture, at a
second end of the line, said signal of determined frequency; and
decoding the corresponding information.
2. The method of claim 1, wherein several additional information
signals are transferred, each being associated with a determined
frequency corresponding to an integer multiple of the frequency of
the digital data samples.
3. The method of claim 1, wherein the oversampling frequency of the
delta-sigma converter is chosen to be much higher than the
frequency of the digital samples.
4. The method of claim 2, applied to a digital-to-analog converter,
wherein said line connects a noise shaping circuit to a converter
over one bit of the digital oversamples, the signal of determined
frequency being mixed to the digital data samples upstream of the
noise shaping circuit.
5. The method of claim 2, applied to a digital-to-analog converter,
wherein said line connects a modulator issuing oversamples over one
bit to a digital decimator, the signal of determined frequency
being mixed to a digital data analog signal upstream of the
modulator.
6. The method of claim 1, wherein the digital data are audio
data.
7. The method of claim 1, wherein said line crosses a galvanic
isolation barrier separating digital and analog parts of the
converter.
8. An information transfer device over a line of oversampled
digital data of a digital-to-analog delta-sigma converter,
including: means for coding at least one information signal in the
form of a signal of determined frequency corresponding to an
integer multiple of a sampling frequency of the digital data input
into the converter; means for mixing, at a first end of the line,
the signal of determined frequency with the oversampled digital
data signal issued by a circuit for shaping the converter noise;
and means for extracting, at a second end of the line, the signal
of determined frequency from the mixed signal.
9. The device of claim 8, further including means for multiplexing
several signals of determined frequencies before the mixing means,
and means for demultiplexing these signals of determined frequency
at the second end of the line.
10. An information transfer device over a line of oversampled
digital data of an analog-to-digital delta-sigma converter,
including: means for coding at least one information signal in the
form of a signal of determined frequency corresponding to an
integer multiple of a sampling frequency of the digital data
restored by the converter; means for mixing, at a first end of the
line, the signal of determined frequency with an oversampled
digital data signal issued by a modulator receiving an analog data
signal; and means for extracting, at a second end of the line, the
signal of determined frequency from the mixed signal.
11. The device of claim 10, further including means for
multiplexing several signals of determined frequencies before the
mixing means, and means for demultiplexing these signals of
determined frequency at the second end of the line.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to the field of
digital-to-analog and analog-to-digital converters. The present
invention more specifically relates to so-called "delta-sigma"
converters which perform a coding/decoding of the digital signals
at a much higher frequency than the sampling frequency, and which
use actual digital-to-analog and analog-to-digital converters on a
single bit.
[0003] The present invention more specifically relates to exchanges
of information, other than the data processed by the converters,
between circuits communicating via delta-sigma converters.
[0004] 2. Discussion of the Related Art
[0005] Delta-sigma converters are used, for example, in modems that
transmit data over a telephone line. In such an application, an
analog part of the circuit connected to the telephone line must be
galvanically isolated from digital inputs/outputs of the modem
connected, for example, to a digital signal processor or to a
microcomputer. Signals other than the actual data must generally
transit through the galvanic isolation barrier of the modem. These
additional signals require additional isolation means, separated
from the isolation means through which the data transit, which is
prejudicial to the cost and bulk of the modem.
[0006] Delta-sigma converters are also used in other applications,
for example, between a digital circuit for processing audio data
and an analog circuit that restores or records an audio signal. In
such applications, it is frequent that information other than the
actual audio data have to be transferred between the digital and
analog parts of the system. The transfer of such additional
information conventionally requires additional links dedicated to
this information.
SUMMARY OF THE INVENTION
[0007] The present invention aims at providing a novel method of
information transfer between two circuits exchanging data via a
digital-to-analog or analog-to-digital converter of delta-sigma
type without it being necessary to provide additional links
dedicated to this information.
[0008] A first solution includes putting aside, on the digital
side, a certain number of bits for this additional information.
However, in addition to the fact that such a solution increases the
number of bits, it is not satisfactory since it transfers
information from the digital circuit to the analog circuit only.
Further, such information then pollutes the actual data analog
signal.
[0009] An object of the present invention is to provide a method of
information transfer which, while enabling the use of a link by the
converter, does not pollute the transfer of actual data.
[0010] The present invention also aims at not modifying the number
of bits over which the converter operates.
[0011] To achieve these and other objects, the present invention
provides a method of information transfer between two circuits
exchanging data via delta-sigma converters, including the steps of:
coding the information in the form of at least one signal of
determined frequency corresponding to an integer multiple of a
frequency of digital data samples; mixing, at a first end of a line
carrying an oversampled digital signal of the converter, the signal
of determined frequency; extracting from the mixture, at a second
end of the line, the signal of determined frequency; and decoding
the corresponding information.
[0012] According to an embodiment of the present invention, several
additional information signals are transferred by being each
associated with a determined frequency corresponding to an integer
multiple of the frequency of the digital data samples.
[0013] According to an embodiment of the present invention, the
oversampling frequency of the delta-sigma converter is chosen to be
much higher than the frequency of the digital samples.
[0014] According to an embodiment of the present invention, applied
to a digital-to-analog converter, said line connects a noise
shaping circuit to a converter over one bit of the digital
oversamples, the signal of determined frequency being mixed to the
digital data samples upstream of the noise shaping circuit.
[0015] According to an embodiment of the present invention, applied
to a digital-to-analog converter, said line connects a modulator
issuing oversamples over one bit to a digital decimator, the signal
of determined frequency being mixed to a digital data analog signal
upstream of the modulator.
[0016] According to an embodiment of the present invention, the
digital data are audio data.
[0017] According to an embodiment of the present invention, said
line crosses a galvanic isolation barrier separating digital and
analog parts of the converter.
[0018] The present invention also relates to an information
transfer device over a line of oversampled digital data of a
digital-to-analog delta-sigma converter, which includes: means for
coding at least one information signal in the form of a signal of
determined frequency corresponding to an integer multiple of a
sampling frequency of the digital data input in the converter;
means for mixing, at a first end of the line, the signal of
determined frequency with the oversampled digital data signal
issued by a circuit for shaping the converter noise; and means for
extracting, at a second end of the line, the signal of determined
frequency from the mixed signal.
[0019] The present invention also relates to an information
transfer device over a line of oversampled digital data of an
analog-to-digital delta-sigma converter, which includes: means for
coding at least one information signal in the form of a signal of
determined frequency corresponding to an integer multiple of a
sampling frequency of the digital data restored by the converter;
means for mixing, at a first end of the line, the signal of
determined frequency with an oversampled digital data signal issued
by a modulator receiving an analog data signal; and means for
extracting, at a second end of the line, the signal of determined
frequency from the mixed signal.
[0020] According to an embodiment of the present invention, the
device further includes means for multiplexing several signals of
determined frequencies before the mixing means, and means for
demultiplexing these signals of determined frequency at the second
end of the line.
[0021] The foregoing objects, features and advantages of the
present invention will be discussed in detail in the following
non-limiting description of specific embodiments in connection with
the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 shows, in the form of a block diagram, a delta-sigma
digital-to-analog converter associated with an information transfer
device according to the present invention;
[0023] FIG. 2 illustrates the spectral distribution of the data and
information transfer in a device such as shown in FIG. 1;
[0024] FIG. 3 shows, the form of a block diagram, a delta-sigma
analog-to-digital converter associated with an information transfer
device according to the present invention; and
[0025] FIG. 4 illustrates the spectral distribution of the data and
information transfer in a device such as shown in FIG. 3.
DETAILED DESCRIPTION
[0026] For clarity, only those elements of the delta-sigma
converters which are necessary to the understanding of the present
invention have been shown in the drawings and will be described
hereafter.
[0027] FIG. 1 shows an embodiment of a delta-sigma
digital-to-analog converter associated with an information transfer
device according to the present invention.
[0028] A delta-sigma converter includes a digital part 1 of
filtering and formatting of data words Td over n bits into a
digital signal Td' over a single bit. Signal Td transits through an
interpolation filter 2 (INTERP) which forms a finite impulse
response filter exhibiting zeros for each multiple of frequency f0
of the samples of signal Td. Filter 2 is generally preceded by a
half-band filter (assumed to be included in block 2) which issues
the samples at a frequency p.f0 to the interpolation filter, p
representing an integer which is higher than or equal to 2. Filter
2 issues digital oversamples at a frequency fs=p.q.f0, where q
represents an integer number. Product p.q is generally higher than
or equal to 64. The n outputs of filter 2 are sent onto a noise
shaping circuit 3 (NS), the function of which is to push back the
quantization noise outside the useful band. Circuit 3 issues signal
Td' over a single bit at oversampling frequency fs. Signal Td' is
sent onto an analog part 4 of the converter, essentially formed of
a one bit digital-to-analog converter (DAC) 5 working at
oversampling frequency fs and issuing an analog signal Ta. The
level of a current sample is determined by incrementing, or
decrementing, the level of the preceding sample according to the
state of the single bit. Converter 5 performs, at its output, a
low-pass filtering to eliminate the quantization noise previously
pushed back outside the useful band.
[0029] FIG. 2 illustrates the operation of such a converter from a
frequency point of view. Useful band bu contains the frequencies
lower than data sampling frequency f0/2 and quantization noise qn
has a gaussian spectral density centered on frequency fs/2.
Frequency fs generally corresponds to a very high multiple of
frequency f0. For example, in audio applications, frequency fs is
approximately 64 or 128 times frequency f0. For a data transmission
by means of a modem, frequency fs corresponds to a multiple
generally included between 96 and 256 of frequency f0.
[0030] The structure and operation of a delta-sigma
digital-to-analog converter is well known and will not be discussed
in more detail.
[0031] According to the present invention, line 6 separating
circuit 3 from converter 5 is used to transmit additional
information with respect to the data. This transmission is
performed at one or several frequencies f1, f2, lower than
frequency fs and corresponding to integer multiples of frequency
f0. In the example shown, two information signals I1 and I2 are
transmitted at frequencies f1 and f2 corresponding, for example, to
two or three times frequency f0. Information signals I1 and I2 are,
for example, formed of binary signals over one bit which pass
through encoders (CODE) 7, 8, transforming these binary signals
into frequency signals at frequency f1. The respective outputs of
encoders 7 and 8 are mixed by a multiplexer 9 (MUX). The output of
multiplexer 9 is mixed with the data signal, at a first end of line
6. In practice and as illustrated in FIG. 1, the mixture of the
output of multiplexer 9 with the digital data is performed,
preferably, upstream of noise shaping circuit 3. It is indeed not
very handy to mix frequency signals with a digital signal over 1
bit. The number of bits over which frequencies f1 and f2 are mixed
depends on the desired amplitude for these frequencies. At the
other end of line 6 (on the side of converter 5), the mixed signal
is sent, on the one hand, to the input of converter 5 and, on the
other hand, to the input of a demultiplexer 10 for detecting the
presence of frequencies f1 and f2 and separating them to restore
the two information signals I'1 and I'2 at frequencies f1 and
f2.
[0032] As illustrated in FIG. 2, frequencies f1 and f2 do not
pollute the data going through the delta-sigma converter. Indeed,
these frequencies are located between the useful band and the
quantization noise distribution around frequency fs/2.
[0033] FIG. 3 shows an embodiment of an analog-to-digital
delta-sigma converter associated with a device that transfers
additional information according to the present invention.
[0034] An analog-to-digital delta-sigma converter generally
includes an analog part 11 formed of a modulator 12
(.DELTA./.SIGMA. MODUL) at an oversampling frequency fs, receiving
an analog signal Ra. Modulator 12 issues digital oversamples Rd'
over one bit at frequency fs. Signal Rd' is sent onto a digital
decimator 13 (DECIM) of a digital part 14 of the converter. The
function of decimator 13 is to convert the oversamples over 1 bit
into n samples Rd at frequency p.f0 (fs/q). Decimator 13 forms a
finite impulse response filter comprising zeros for each multiple
of frequency f0 and performs a low-pass filtering of signal Rd'.
The outputs of decimator 13 generally transit through a half-band
filter (assumed to be included in block 13) which brings back the n
samples to frequency f0 and issues signals Rd over n bits.
[0035] FIG. 4 illustrates the frequency response of an
analog-to-digital delta-sigma converter. The quantization noise qn
is, as previously, of gaussian form and is centered on frequency
fs/2. The frequency response of modulator 12 exhibits zeros for
each multiple of frequency f0. Decimator 13 eliminates any
frequency higher than the useful band bu of the converted
signal.
[0036] As for the digital-to-analog converter, the structure and
operation of an analog-to-digital delta-sigma converter is well
known and will not be discussed in further detail.
[0037] According to the present invention, to transmit additional
information over line 15 separating modulator 12 from decimator 13,
one or several frequencies corresponding to integer multiples of
frequency f0 are used, as in the case of the digital-to-analog
conversion. If several additional information signals have to be
transmitted, these information signals are, as previously,
multiplexed (MUX 16), and are here mixed with signal Rd'. The
mixture is, preferably, performed upstream of modulator 12, that
is, on signal Ra. At the other end of line 15, the signal is sent
on the one hand to decimator 13, and on the other hand to a
demultiplexer 17 (DEMUX) for detecting and isolating frequencies f1
and f2 to restore the transmitted information. Of course, as in the
case of the digital-to-analog conversion, the additional
information may be coded upstream of multiplexer 16 and decoded
downstream of demultiplexer 17.
[0038] As can be seen in FIG. 4, the transfer of the additional
information at frequencies f1 and f2 does not pollute the data
since these frequencies f1 and f2 are filtered before restoration
of data Rd. Indeed, these frequencies correspond to zeros of finite
impulse response filter 3 and are included between the useful band
of the converter and the quantization noise distribution around
frequency fs/2.
[0039] If, for reasons of practical implementation convenience, the
fixed frequency signals are, for a transfer using the
digital-to-analog converter, generated in the form of digital
frequencies to be mixed with the actual data and, for a transfer
using the analog-to-digital converter, generated in the form of
analog signals to be mixed with the analog data signal, these
signals can also be mixed with the oversampled digital signals over
1 bit, that is, at the output of circuit 3 (FIG. 1) or at the
output of circuit 12 (FIG. 2). The number of additional information
signals that it is possible to transmit by implementing the present
invention depends on the ratio between oversampling frequency fs
and frequency f0. Thus, delta-sigma converters having a much higher
oversampling frequency than frequency f0 will preferably be used.
This condition is perfectly compatible with the usual ratios
between frequencies fs and f0 in audio applications or applications
of digital data transmission by means of a modem.
[0040] To implement the present invention in a modem of digital
data transmission between a user's equipment, for example, a
microcomputer, and a telephone line, the galvanic isolation between
the telephone line and the user's equipment is, according to the
present invention, performed between the digital (1, 14) and analog
(4, 11) parts of the delta-sigma converters. Thus, additional
information such as control signals and signals for programming the
analog part can transit through the same isolation barrier as the
data without requiring additional isolation means.
[0041] In a system for restoring or recording sound signals coded
in digital form, the implementation of the present invention
superposes on the same line (6, 15) both the audio data and the
control signals (for example, a volume control for the analog sound
restoration part).
[0042] An advantage of the present invention is that it reduces or
minimizes the number of connections needed to transmit information
between circuits exchanging data by means of delta-sigma
converters.
[0043] Of course, the present invention is likely to have various
alterations, modifications, and improvements which will readily
occur to those skilled in the art. In particular, the practical
implementation of the coding of the information signals to be
transmitted and of the possible multiplexers and demultiplexers is
within the abilities of those skilled in the art according to the
functional indications given hereabove. Further, the number and the
choice of the frequencies of transmission of the additional
information depend on the application for which the device of the
present invention is meant, provided that these frequencies always
correspond to integer multiples of the data sampling frequency.
Further, the present invention applies to any system of conversion
respecting the features of 1 bit delta-sigma converters, that is,
exhibiting a transfer line of data oversampled over 1 bit. Such
alterations, modifications, and improvements are intended to be
part of this disclosure, and are intended to be within the spirit
and the scope of the present invention. Accordingly, the foregoing
description is by way of example only and is not intended to be
limiting. The present invention is limited only as defined in the
following claims and the equivalents thereto.
* * * * *