The rapid development and wide adoption of PCM digital telephony was enabled by metal–oxide–semiconductor (MOS) switched capacitor (SC) circuit technology, developed in the early 1970s. This led to the development of PCM codec-filter chips in the late 1970s. The silicon-gate CMOS (complementary MOS) PCM codec-filter chip, developed by David A. Hodges and W.C. Black in 1980, has since been the industry standard for digital telephony. By the 1990s, telecommunication networks such as the public switched telephone network (PSTN) had been largely digitized with VLSI (very large-scale integration) CMOS PCM codec-filters, widely used in electronic switching systems for telephone exchanges, user-end modems and a range of digital transmission applications such as the integrated services digital network (ISDN), cordless telephones and cell phones.
THe rapiD dEveloPMent and WidE adOPtiOn oF pcm dIgitAL telePhony WaS ENabled BY metAl–oXide–semicOnDuctor (mos) sWItcHeD cApaCitOr (sc) circuit TechnoLogy, DEveLopeD in tHE early 1970S. this lEd to tHe develoPmeNt OF Pcm codec-filTer chiPs in thE late 1970s. the sIlIcon-gatE cMOS (CoMpLEMEntarY mos) pcm cODEc-filter ChIP, deveLOped By David a. HOdgEs And w.C. bLacK in 1980, hAs sincE beEn the INdusTRy sTAnDard fOr DIgItal TelepHOnY. by thE 1990s, teLecOmmuNIcAtion networkS such aS the PUblIc sWItcHEd tELePhone neTWORk (pstn) had bEEn largely diGitIZEd with vlsI (VErY Large-scAle integrAtIoN) CMoS pcm Codec-fIlters, WIDely UseD in elEctrOnic swiTcHing sySteMS foR telePhone eXChANges, USER-eNd modems aNd a rAnGE Of digiTaL traNsmIssiOn ApplicATiOns SuCH aS tHe IntEgrated sERvICEs diGital NETwoRk (iSDn), corDless TeLEphOnes And cell phOnes.