An Oversampling Adc With Non-linear Quantizer For Pcm-codec

Abstract

This piper clescrihes rtri overxinipling cinnlog-io-digitctl converter (ADC) suiirible for PCM codecs. Non-linear 5-level quctrttiier is iiiipleiiwiied to the itoise-s/iaping modulator. This ADC cun sciti.$fi the specifications of CCITT G. 712. in .siii/e of using ,firs[ order delta-siRma irioddrttor rinc/'reniiie.s low xwer opemfiori. This clrip is fdJriccitcd in O.t+iii dou/i/e-po/y (im/ dr,uL/e-rnetci[ CMOS lirocess orid occupies clrip urefi of 1Snim2. The ruri.riinuni power consurnpiion is 12.8m W with u single +3Vporver supply iwludirig DAC ciml TONE genercttor. INTHODUCTION Oversampling ADCs and DACs usin second order delta-sigma modulatorsl) or interpolation modulators8 have been developed for applying PCM codecs along with the progress of VLSI technology. However. the second order delta-sigma modulator requires sever specifications",, for SCF circuits such as high low-frequency open-loop voltage gain over 70dB for each operational amplifiers, small settling error lower than O.S%, and small relative enor of capacitors less than 0.2%. Hence it is difficult to realize operational amplifiers satisfying these severe specifications with low power consumption. The interpolation modulator needs the local DAC having 7b equivalent precision and it causes large area of analog circuits compared with other oversampling techniques. Thus we have proposed a new conversion scheme of ADC suitable for PCM codecs with paying attention to the SNR specifications defined as CCITT G.7 12. As a result, it can satisfy the needed SNR by introducing the non-linear S-level quantizer, in spite of using the first order delta-sigma modulator.