BSTJ 50: 4. April 1971: A Digital Approach to Adaptive Delta Modulation. (Goodman, David J.)

2.8 MB·English

A Digital Approach to Adaptive
Delta Modulation

Uy DAVID J, GOODMAN
(Stasi sted Noverbo #,10

size ella modutotar followed ty dita eet for

A fi
senoratng sn eagle dee mniultin sire provides
umpromite beteetn code efeioney ond ust In order to zontrol the
total quantizing noes, the fradheteprse delta modulation sampling
te ie hpher than the adepive nelix movwletion output vate.
‘puter rinlacione, bated on the edaptive delty modulation technique
Aeseribed by X. 8. Jayont, indicate thet the sampling rate required
far neghinble degradation relative fo a conventionat adaptive dele
‘modula ss well within the eveant stats of the art. Ox oppreach
Tends itself to any scheme of stepaize veriaton and may te en
menns of sinlecintepration, Rendateprise delta wodhtation.

Since che invention of della mowiatin, wonsidorae eff hae
heen devoled la devi, mean ot inmproving ele efilency wich
2ecrideing the inherent simplisty of tao analogzo-diial converter.
‘The key to succese in this respect is the setention ofa singe binary
dosision Zor cach sample ofthe azaing input. Key Ravk concentrated
fn sophisticated linear eigaal processing to he introduced ether a
the Input tothe dee wodulator, ne preditar in te feabuek loop,
for as ar error iter in the forwesd Woop’? Tn recent yeurs, the use
of a time-varying stop igs an the feodbaek ‘oop hae bees capha-
Sined'® Althngh he steyesne entation, se sense, tearm the
le malas fen ry co» mulilevel devge plementation
ie Ezely to be move coonomioa than ths: ef a ontentiunal maltileve
Qquancize. The varishleatep sine, sometinis etd “uiapive” oF
“oompanding.” mechani provides contlecuble provement in
afiienoy and i: 6 poisble tat for epeceh encading, thie tiem of
Vere an evsrmne raceteat, Touma, AT, eT

Getty mesutation wll zesuls in Delt posformance eharaeiersies fs
the 20-40 Iiloitjeecont range tbun eoaventional PCM

‘the purpose ef Ks paper ie to ovesort w new approrch to the
smplencentation of adaptive dela modulators, Thr approach ie matix
Selel hy eurent trnde in revise daviee technology thet susgest
thas clgial harénate implementvione heees x stanrdiaedetding
blocks ‘ill offer alvaatages of econoray and Nexility relative. 0
fnnlog tshiques. Tais hypulesie eombized wilh the observation
Shut tnentmnion rate rather thaw onsiog-to-tatel conversion vate
Soflucns lhe overall coat of digital eompnniestion system stgrsta
fhe uae of fhe very simple sigheinteration della modulator for
Enulog-toligilal conversion aad gal berdware for conversing the
Shales iesgre ins, fisesnnapesaerepresestatios Uo he deste eieient
feamet. Thy seyststing snslos-losigtal eogversion from source exe
coding, ye elvan compromise Iebween the gous 0: etonomy 6°
Implencoruion and ficiency of eprezantstion, This compromise,
based on the addition of only digice! devious to the wile dete
rnodulstr, promise, ia many sisson, to be more ecorouieal than
he conventions] ajytoeeh of petforring acus-loyisl conversion
Sn ezareo ending sn one step, This paint of view Ins ed ta a now
tyne of PCM eneoler thar combines a delle modalacoe with & none
reuse dita Her

‘The digits! rienits required to convert » simple den modution
signal to a vavinblescepsige forse comprise 4 "digital delta modu
Tater” opeseng om Ue Svegsatad entre of the Bist delta modulator
Thu edetion to w staentiat irae tot determines the appsoprite
step ian a euch instant, che éigital delta modular cmtsing oniy
inary counting vel wMlitice eens ez ace simple dessin elemaeat.
[Fygure Lien operational bloc dageamn uf the entice encoder.

Computer simulations Inve verified the Zeaibity of the eombie
naaion of xad-tep-nite delta moulatar ana s digital deltw morla-
Ince. N.S. ayant’ sehere of slap delta modulation? was srt
loa Ty tieana of eofoware provide by Jeyant-anc Mae K. Shipley
Fora given output rst the operation of The digital deta moduetor
in Figs 1 is determined eompetely by Uhe sleposize lgie. Ac cech
Ineteal the slay sie depends on the provious step ize end the ox
i)
ent and previnsbinaey outputs T the binary oulsuts ae identical,
the caren! step ine [5 times the previous exp sine; 1 they fer,
Sh is 0.65 tice the previous step size. Lo ation tothe autput rate
Of ile digial dats molator, she design paranectora io Tig. 1 are
She wep sow and sampling rate ul the Sxed-stopsine deka mola
Je our smulaous, tae prot of step size asl sampling ret,
ius the mexinune slope of (ie delta madulitor, wae Seld constant
‘This eumtent. was ebones on le hese of previous simulations 2
Iuyant of Bxed-step-'se dela Tndalators tpoenting ox the ech
“agp used in our emulations,

‘Gur wets aze sbown in Fig. 2 as eurvee of ouput signsi~io-oine
ratiy (5/9) plotted noainet the sampling rate 0° the fxed-cop-sie
{elle nodular for two different outpat sates [by vot urpnising that
for low sampling sates 0 the fret delte moduler, iti th error per~
Fornuaee 0! hie deve tout, Tgely determin the overall S/N. A
Ue sapling rate ere, he insegeated outpuve the e-stepsize
tle modulator becomes ariverily claes to the unalog input and the
Aevmmolacie BY ie Mentioal ta that of aa wlaplive deta moduletor
Sevating Giectly on the analog input. (A sepia wiration hee
‘ecified this statement.) ‘The siviulation results are quite encouraging

Fig, Poems dncsleriins
soserive autre sown aan
heause they shew thet for tke ourput rates eosidered, which ane in
the rango of practical intrest, the hiheped samme rae request
for rehgible performanoe degradation relative to x romventions)
lnnplemeneaion is we) within fe sate of dear

[By contrast with This empties! mea of deternining Ue ral al
step tee of he high-epees celta masletor oe may take te follow
ing conservative appzoach: (0) Ser the sep sue athe ina step
fine of the ative celle orlatos, Une nssusiag the the quaotising
ecetution is not compenmieed nnd 1) let the high-speed lock Zale
‘be te zal autput eats timas the ratio of main taal sap
sine 20 thas the maxinnin shpe iv vo! reduced A typieal ratio ef
rpesizoun fo minimum le sie 12831 so that th a ouput rato ef
(kb, the Axed-eop-rne seke mult ead to operate st
$5102 Ills seeording to this eonsey ative cites

Figure | ie fanetionel blk diagram whieh indent the sequired
en proeeesing operations. Ir « hardware implementation, east
‘rable simplifea:ion is peeible. The wp-ciwu euunver ard ie cer
snd necumulstor of the digital delta molator may be combined ix
¥ sioale acoumultor ce show: ia Fig $.'This areulatae se raise
by Hl or 1 Zor each suple of the fixed-eteperize delta molator
std ie changes Sy che maguiiste he lap sige al exe output
sampling instant.

‘The two-level quantisee éetersines the polarity af earn outpt
hulse geeordng to the ete of ingle bit ofthe aevumulstor. The
epee logie provides a digital wvneaetation uf te rurromt sep
site, Various mane of ning 1h ‘adation ane possible, eveh
ppropriste to a diferent scheme of alep-size Variation, One method
involves ekocsing th et size Stam» "lctgracy" nesuding to he
fxspat state of the adaptation foie. This terhninun lends vise co
Fnpleesetation by ener af atabcetaie-up” Sons w at 0 vead-on'y
rremory registers, each containing ane of the jssble step sins
Another toeinique ae to specify {heures rlepriar we on writes
funtion of she previces step 2ize—fo> example wmtltnke of or inero-
mental ehange frm the peviows ste ine, For this type of adapon,
he digs) delta nsulaior sould eunveniently contain e maiae
roicter which is azithmetically modified according to the output of
{the adapeation Inge.
1428 re aut svete meiveat FOURMAL, APRIL 197

ig, Sind plenecaon,

‘The echxigue deseibed in this puoee combinos the simplicity of
antloy-todigital eonversan provided by five-sta-sie della mec
Jasion With the code ofioney 0! weriuble-step-size delta modulation,
Gnily'« ezgle rep sie sort be precisely contre wich analog Bl
Wrote; the step-ine vacation by controlled digitally, nd is Uierefone
Srl The techni lanes Ite to wny sohvine of eop-see variation
nd eng means of fxed-tepeie, siale-integration dete modulation

sani aE ted Guay, J.

HET tg nme yo” lt. Oe

‘ecmd 73, Por. Moreh 189), pp, 280-988
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