GB2242798A

GB2242798A - Analog to digital converter

Info

Publication number: GB2242798A
Application number: GB9107023A
Authority: GB
Inventors: Marcello Boella; Giampaolo Dian
Original assignee: Marelli Autronica SpA
Current assignee: Marelli Europe SpA
Priority date: 1990-04-05
Filing date: 1991-04-04
Publication date: 1991-10-09
Also published as: IT9067251A1; DE4110946A1; GB9107023D0; IT1240168B; IT9067251A0; FR2660815B1; FR2660815A1

Abstract

An analog/digital converter (4) samples the signal supplied to its input at a predetermined sampling frequency (fc) and generates a digital representation of the values sampled in a pre-established code with a predetermined quantisation range or band. A generator (6) generates a periodic signal (B) with a frequency (f) lower than the sampling frequency (fc) and a peak-peak amplitude at least equal to the amplitude of the quantisation range of the analog/digital converter (4), the periodic signal (B) being superimposed on the received analog signal (A) to be converted. A storage device (8) adds the digital values supplied by the analog/digital converter (4) within a period of time of predetermined duration. <IMAGE>

Description

1

DESCRIPTION

The present invention relates to an analog/digital conversion system and more specifically to a system including; an input for an analog signal to be converted into digital form, and an analog/digfltal converter arranged to sa.,,,inle a signal supplied to its input at a predetermined sampling frequency and to generate a digital representation of the values sa.rroled in a Ere-establ-4s&lecl code with a Dredetermined quantisation range or band.

The object of the present _Js to pprovide an analog/digital conversion systei-,,i witb i-inn-roved According to the invention, this object- is achieved by meanA of an an. alocr/d-Ja.,ik'.-al conversion syst-em of: the type specif led above, whose ma in innovative characteristic lies in the fact that it also includes a genetator for generating- a per-ic,,c5-Jc with a frequency lower than the sampling frequency and a peak-peak amplitude at least equal to the of the quantisation range of the ana!Qg/digital converter, and means for superimposing the periodic signal supplied by the generator on the analog signal applied to the input and applying the resulting signal to the i-.-.put of the analog/digital conver,"--er.

1 According to a further characteristic, the periodic-signal generator is preferably a triangular-wave signal generator.

Further characteristics and advantages of the invention will become clear from the detailed description which followsi with reference to 1Che appended drawings, provided purely by way of non-limiting example, in which:

Fiaure 1 is a block d-4agram showing the structure of an analog/dig-1tal conversion system according to the invention, and Figure 2 is a series of exDlanatorv cra,;:,hs useful for 1 - an understanding of the way in tj'.-.-ich the syste-m according to the - inven.11..1o--i works.

With re-.erp-nce to Figure 1, an ana'Log/digital co,-.ve.-sion system according to the Invention, generally indicaiL'-ed 1, has an input 2. fOr an analog signal to be converted into digital form and a multi-wire output 3 from which the digital representation of the sampled values of the signal is emitted.

The system includes an analog/d_lgital converter 4 of known type, for example, of the single-slope or nega'c--ive-feedback type. In oteration, the analog/digital converter samples the analog signal supplied to its input at a saxipling frequency z c (for exampler 5 kHz) set by an oscillator 5 and generates a digital representation of the values sa=, pled in a r,re-es-"Lablished code with a predetermined quantisation range or band.

J 1 3 A generatorr indicated 6t generates a periodic signal with a frequency f which is lower than the sampling frequency f c and hlas a peak-peak amplitude at least equal to the amplitude of the quantisation range of the analog/digital converter 4. The generator 6 is, f or example, a generator of known type which generates a triangular-wave signal, preferably (but not necessarily) with a zero mean value.

The signal supplied by the generator 6 is superimposed on the analog signal applied to the input. 2 at a node or adder 7 and the resulting signal is applied to the inDut of the converter 4.

The output of the converter 4 is connected a storage device 8 which is adapted to add the digital values supplied by the converter 4 within a Deriod oil 0= pre-established duration. This device may include, lor example, memories and an adder for retainingr, at any moment, -thle last n values corresponding to the last n analog values sar-pled and outiDuttil-.g an indication oi the sum or of a mean value of those last n digital values.

The superimi-osilb-ion of the periodic signal supplied by the generator 6 on the analog signal to be converted Into digital forn., improves the resolution of the conversion, as will now be explained further with reference to Figure 2.

Figure 2 shows, by way of example, the curve A of an analog signal applied to the input 2 of the conversion.

system 1. The quantisation r. a.r. g e O.L the analog/digital converter 4 is jndl'cal-ed Q. The portion of the signal A shown in Figure 2 falls 4 entirely within a certain quantisation range which is assumed to be associated with the digital value "100". if the signal A shown were applied to the input of the converter 41 the converter would always outpull: the signal "100" since the variation of the signal is more restricted than the amplitude of the quantisation range Q and the signal does not, therefore, cross into adjacent quantisation ranges.

A curve, B of the Deriodic (triangu, lar -wave) signal output by the generator 6 is shown. by way of example, in Figure 2. The frequency f = 1/T of this signal is lower than the sampling -f-requency 'L c of the converter 4 and is, for example, about one thirty-second of that,;. requency. The peak-peak airiD!-ijl..ude of the signal Bt indicated a in Figure 2, is (at least) equal to the an.plitude of the quantisation range 0.

Still with reference to Figure 2, the mean value of the signal A + l thus follows the curve of the signal A. The signal A + B is not entirely contained within the quantisation range _In which the signal A remains (in the example illustrated) but, for a period of time tly crosses into the range or band above, which is associated with the digital value "1- 01", and, for a period of time tV, crosses into th.e ranae or band below, which is- associated with the digital value 1101121.

in operation, the converter 4 in the conversion system 1 thus converts the signal A +]8 into -digital Still with reference to the sit,41.a,,-iQn shown by way of example in Figure 2, when the signal applied to the input 2 assumes the curve indicated A j..,1 Figure 2, therefore, t_he converter 4 no longer always outputs the -i value "100" but:

before the period t 1 it provides the value "100", during the period ti it provides the value "101, between the perlods.t 1 and t2 it provides the value "100".- during the period t 2 it provides the value "Oll", and after the interval t2 it provides the value "100" again.

It is clear from the foregoing explanation that, as a result of the super imposition of the signal 3 on the signal A, the values output by the converter 4 constitute a more' faithful representation of the behaviour of the signal A to be converted into digital form and hence achieve better resolution than the representation which would be produced by the application of the signal A directly to the inpug'-- of the converter.

The periodic signal superimposed on the analog signal to be converted into digital forn need not necessarily have a zero mean value; a mean value other than 0 simply involves the appearance of a "constant" component, that is, a constant "o.-c6,iE"set" value _In the values output by the con.er51on system, which can easily be eliminated in known 7iianner.

Moreover, the signals output by the analocj/digital converter of the system according to the invention may be manipulated in ways other than that shown in order to extract mean values of th.e set of signals or of subgroups thereof conventional mathematical techniques.

-v, X

Claims

1. An analog/digital conversion system including:

an input (2) f or an analog signal (A) to be converted into digital form, an analog/digital converter (4) arranged to sample the signal supplied to its input at a predetermined -sampling frequency (f c) and to generate a digital representation of t h. e values samiled in a pre-established code with a predetermined quantisation range or-bande characterised in that it also includes:

a generator (6) for generating a periodic signal with a frequency (f) lower than the samt^ling frequency (.f and a peak-peak. amplitude (a) at leasi.. equal to IL-11,4e amplitude of the quantisation range (Q) of the analog/digizal converter (4), and n means (7) f or superimposing the periodic signal (B) supplied by the generator (6) on %.he analog signal (A) aPplied to the inout, (2) and applying the resulting signal (A + B) to the input of the analog/digital converter (4).

2. A system according to Claim lt characterised in that it also includes storage means (8) for adding the digital values supplied by the converter (4) within a period of time of predetermined duration.

3. A syste-nt according to Claim 1 or Claim 20 characterised in that the generator (6) is arranged to generate a periodic signai (5) with a zeto mean value.

4. A system according to one of the preceding claims, characterised in that the generator (6) is a triangular-wave signal generator.

5. A system according to Claim 1. characterised in that the storage means (8) include memory and adding devices adapted to retain, at any moment. the last n digital values corresponding to the last n analog values sampled and to output an indication of the sun, or of a mean value of the last n digital values, n being a predetermined whole number.

6. An analog/digital conversion system substantially as described he-rein with reference to the acccmpanyi'ng drawing.

-..I Published 3991 at The Patent Office. Concept House. CardilT Road. Gwent NP9 I RH Further copies mas. be obta n d from Mfelinfach. Cross Keys. Newport. NPI 7HZ. Printed by Multiplex techniques ltd. St Mary Crav, Kent Sales Branch. Unit 6. NineMile Point. Cl'