FR2660815A1 - ANALOG / DIGITAL CONVERSION SYSTEM. - Google Patents

Abstract

Analog-to-digital conversion system comprising an analog-to-digital converter (4) designed to sample the analog signal (A) supplied to its input at a predetermined sampling frequency (fc) and to construct a digital representation of the sampled values according to a code preset with a predetermined quantization range or band (Q), a generator (6) to generate a periodic signal (B) of frequency (f) lower than the sampling frequency (fc) and of peak-to-peak amplitude (a ) at least equal to the amplitude of the quantization range (Q) of the analog / digital converter (4), the periodic signal (B) being superimposed on the analog signal (A), storage devices (8) adapted to add the digital values supplied by the analog / digital converter (4) during a predetermined period of time.

Description

ANALOG / DIGITAL CONVERSION SYSTEM

  The present invention relates to an analog / digital conversion system and more specifically, a system comprising: an input for an anatogic signal to be converted into digital form, and a logic / digital anat converter designed to sample L Lttonner a signal supplied at its input at a predetermined sampling frequency and in order to develop a digital representation of the sampled vectors, according to a pre-set code with a

  dynamic or predetermined quantization band.

  The aim of the present invention is to provide a logic / digital ana conversion system.

improved resolution.

  In accordance with your present invention, this object is achieved by means of an anatogic / digital conversion system of the type mentioned above, and the main innovative characteristic of which resides in the fact that it also includes: a generator for preparing a signat periodic of frequency lower than the sampling frequency and peak-peak amplitude at least equal to the amplitude of the quantization range of the analog / digital converter, and a means for superimposing the periodic signal provided by the generator on a signal anatogic applied to the input, and apply the resulting signat to the input of the anatogic / digital converter. Another feature of the system is that the periodic signal generator is preferably a waveform signal generator.

triangu Ltaire.

  Other features and benefits

  of the invention will emerge from the description

  detail presented below with reference to the accompanying drawings which are provided without limitation of illustration of the invention and in which: FIG. 1 is a functional diagram representing the structure of a logic / digital ana conversion system from - the invention, and FIG. 2 is a series of explanatory graphs facilitating the understanding of the mode of

  -invention system operation.

  Referring to FIG. 1, an anatogical / digital conversion system of the invention, generally designated at 1, has an input 2 for an analog signal to be converted into digital form and a muttifity output 3 from which is issued the digital representation of

  sampled signatory data.

  The system includes an anatogic / digital converter 4 of a known type such as the

  single slope or negative feedback type.

  When it works, the ana Logic / digital converter samples the anatogical signal supplied at its input at a sampling frequency L L tonnage fc (for example 5 k Hz) fixed by an oscillator 5 and draws up a digital representation of the sampled vectors Data is based on a pre-established code with a predetermined quantization band or band. A generator, designated at 6, generates a periodic signal at a frequency f which is lower than the sampling frequency fc and has a peak-peak amplitude at least equal to the amplitude of the quantization range of the analog / digital converter 4 The generator 6 is, for example of a known type which generates a triangular waveform signal preferably having (but not

  necessarily) an average value nu-tle.

  The signal-1 supplied by the generator 6 is superimposed on the anatogic signal applied to the input 2 at a node or an adder 7, and the resulting signal is applied to the input of the

converter 4.

  The output of the converter 4 is connected to a storage device 8 which is suitable for adding -the digital values supplied by the converter 4 during a time interval of preset duration. This device can for example include memories and an adder for retaining, at any time, the last N digital values corresponding to the last N sampled analog values and producing an indication of the sum or an average value of these

n latest digital values.

  The superimposition of the periodic signal supplied by generator 6 on the analog signal to be converted into digital form improves the resolution of the conversion, as will be explained below.

with reference to your figure 2.

  FIG. 2 represents, by way of example, the curve A of an analog signal app-liqued at the input 2 of the conversion system 1 The quantization range of the anatogic / digital converter 4 is indicated by Q The part of the signal A shown in Figure 2 is located entirely within a certain quantization point that we will assume to be associated with the digital vector "100" If the sign A shown was applied to the input of converter 4 , the converter would always produce the signal "100" because -ta variation of the signal is less than the amplitude of -the quantization plate Q and the signal does not cross

  not The adjacent quantization pages.

  A curve B of the periodic output signal (triangular wave) of the generator 6 is shown by way of example in FIG. 2 The frequency f = 1 / T of this signal is less than the sampling frequency fc of the converter 4 and is by

  free equal to 1/32 of this frequency.

  The peak-peak amplitude of the sign B indicated in a in your figure 2 is (at least) equal to the amplitude of -ta p Quantization rate Q. Referring always to figure 2, your average vector of the signal A + B therefore follows The curve of signal A Signalt A + B is not entirely located within your quantization range within which signal A remains (in the example shown) but during a time t 1, it enters the range or The band situated above and which is associated with the digital driver "101" then for a time t 2, enters the p-ltage or-your band situated in- below, and that is

  associated with the digital vector "011".

  In operation, the converter 4 of the conversion system I therefore converts

  -your signal A + B in digital form.

  Always referring to the situation shown as an example in Figure 2, twisted -The app signal Liquefied at -the input 2 adopts the curve indicated in A in your Figure 2, -the converter 4 does not provide ptus permanently -the value "100" but: before Period t 1, it supplies your vector "100" during -ta period t 1, it supplies the vector

"101",

  between periods t 1 and t 2, it provides -the value

"1 00",

  during -the period t 2, it supplies the value "011", and after you intervene it t 2, i-l supplies again -ta

go to Their "100".

  It is clear from the explanation given above that, due to the superposition of signal B on signal A, your values produced by converter 4 constitute a more faithful representation of the behavior of sign A to be converted under numerical form and therefore, allow to obtain a better resolution than -y representation which would be produced by -Applying the sign A directly to -The input

of the converter.

  It is not necessary for the periodic signal superimposed on the analog signal to be converted to digital form to be of average zero; the only effect of an average different from O is that a "constant" component appears, that is to say a constant bias in the values produced by the conversion system, which can

  easily be eliminated in a known manner.

  In addition, the signals produced by the analog / digital converter of the system of the invention can be manipulated by methods other than those indicated here, in order to extract the average values of the set of signals or of sub- groups of these signals, by techniques

classical mathematics.

  It is obvious that, while retaining the basic principle of the invention, your embodiments and details of the structure of the system can be modified to a large extent compared to those which are described and illustrated. non-limiting examples, without you

  departs from the scope of the present invention.

Claims (5)

  1 Analog / digital conversion system comprising: an input (2) for an analog signal (A) to be converted into digital form, an ana-logical / digital converter (4) designed for sampling L Lttonner -le signa-l supplied at its input at a predetermined sampling frequency (fc) and to develop a digital representation of the sampled values according to a pre-established code with a predefined quantization band or page, characterized in that it comprises: a generator (6) for developing a periodic signal of frequency (f) lower than -ta frequency of sample L Lonnage (fc) and a peak-peak amplitude (a) at least equal to -The amplitude of your quantization range (Q) of the analog / digital converter (4) and a means (7) for superimposing the periodic sign (B) provided by the generator (6) on the anatogic sign (A) provided at the input (2), and apply the remaining signal (A + B) to the converter input analog / digital (4).   2 Lton system Claim 1, characterized in that it also includes storage means (8) for adding -the digital values provided by the converter (4) during   a period of predetermined duration.   3 System according to claim 1 or 2, characterized in that the generator (6) is designed to develop a periodic signal (B) from the vector average zero Le.   4 System according to any of   previous claims, characterized in that   generator 6 is a shape sign generator triangular wave.   5 se-ton system -ta claim 1, characterized in that -lte storage means (8) includes a memory and addition devices adapted to keep at any time, -The n last digital vators corresponding to the N last vateurs analog samples L Data and to provide an indication of your sum or an average vator of the N last numerical values, N being a predetermined whole number.