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  • Modellingof

    Power Dissipationin

    CMOS DACs

    Sofie Jrgensen

    LiTH-ISY-EX-3275-2002March 14, 2002

  • Avdelning, Institution Division, Department

    Institutionen fr Systemteknik 581 83 LINKPING

    Datum Date 2002-03-14

    Sprk Language

    Rapporttyp Report category

    ISBN

    Svenska/Swedish X Engelska/English

    Licentiatavhandling X Examensarbete

    ISRN LITH-ISY-EX-3275-2002

    C-uppsats D-uppsats

    Serietitel och serienummer Title of series, numbering

    ISSN

    vrig rapport ____

    URL fr elektronisk version http://www.ep.liu.se/exjobb/isy/2002/3275/

    Titel Title

    Modellering av effektfrbrukning i CMOS DA-omvandlare Modelling of Power Dissipation in CMOS DACs

    Frfattare Author

    Sofie Jrgensen

    Sammanfattning Abstract I det hr examensarbetet har effektfrbrukningen av en current-steering digital-analog omvandlare studerats. Den digitala samt den analoga effektfrbrukningen har modellerats mha MATLAB och modellen stmmer vl verens med resultaten frn kretssimulatorn (Spectre). In this master thesis work, the power dissipation in a current-steering digital- to-analog converter, DAC, has been studied. The digital as well as the analog power dissipation have been modelled in MATLAB and it is shown that the MATLAB models agrees well with simulation results from the circuit simulator (Spectre). A case study on a DAC designed at Ericsson Microelectronics AB in Linkping has also been done. The DAC is a thermometer-coded current-steering DAC suitable for telecommunications applications. The telecommunication standards that have been studied are asymmetric digital subscriber line, ADSL, very high speed data digital subscriber line, VDSL, and, wireless local area network, WLAN. The conlusion of the study is that the power dissipation of the specific DAC, used in ADSL applications, 75mW, is far from optimized. It can theoretically be lowered to 3.5mW.

    Nyckelord Keyword DAC, power consumption, power dissipation, telecommunications

  • Modellingof

    Power Dissipation in

    CMOS DACsExamensarbete utfrt i Datorteknik vid Linkpings Tekniska Hgskola

    av

    Sofie Jrgensen

    LiTH-ISY-EX-3275-2002

    Handledare: Niklas Andersson, Ericsson Microelectronics ABOla Andersson, Ericsson Microelectronics AB

    Examinator: Mark Vesterbacka, Linkpings UniversitetLinkping den 14 mars 2002

  • AbstractIn this master thesis work, the power dissipation in a current-steering digital-to-analog con-verter, DAC, has been studied. The digital as well as the analog power dissipation have beenmodelled in MATLAB and it is shown that the MATLAB models agrees well with simulationresults from the circuit simulator (Spectre).

    A case study on a DAC designed at Ericsson Microelectronics AB in Linkping has also beendone. The DAC is a thermometer-coded current-steering DAC suitable for telecommunica-tions applications. The telecommunication standards that have been studied are asymmetricdigital subscriber line, ADSL, very high speed data digital subscriber line, VDSL, and, wire-less local area network, WLAN. The conclusion of the study is that the power dissipation ofthe specific DAC, used in ADSL applications, 75mW, is far from optimized. It can theoreti-cally be lowered to 3.5mW.

  • Table of Contents1 Introduction .................................................................................................................... 1

    1.1 Brief Overview of the Report ...................................................................................................... 11.2 Aim and Goal............................................................................................................................... 1

    1.2.1 Limitations .................................................................................................................... 21.3 Method......................................................................................................................................... 21.4 Telecommunication...................................................................................................................... 3

    1.4.1 Introduction to Telecommunication .............................................................................. 3

    2 Digital-to-Analog Converters......................................................................................... 72.1 The Ideal DAC............................................................................................................................. 72.2 DAC Performance Measures ....................................................................................................... 8

    2.2.1 Static Performance Measures ........................................................................................ 82.2.2 Dynamic Performance Measures ................................................................................ 102.2.3 Frequency-Domain Measures ..................................................................................... 10

    2.3 Nyquist-Rate DACs ....................................................................................................................112.3.1 DAC Architectures .......................................................................................................112.3.2 Implementation Modes for DAC................................................................................. 12

    3 CMOS Power Dissipation ............................................................................................ 153.1 General Power Dissipation for CMOS ...................................................................................... 153.2 Power Dissipation in the Digital Part ........................................................................................ 15

    3.2.1 Measures of Power Dissipation in the Digital Part ..................................................... 163.2.2 Minimizing the Power Dissipation in the Digital Part ................................................ 18

    3.3 Power Dissipation in the Analog Part........................................................................................ 213.3.1 Fundamentals of Noise................................................................................................ 213.3.2 Different Types of Noise ............................................................................................. 223.3.3 Noise Models............................................................................................................... 233.3.4 Mixed-Signal Layout Considerations for Low Noise ................................................. 23

    4 Case Study.................................................................................................................... 274.1 Market Study of DACs .............................................................................................................. 274.2 Thermometer Coded Current-Steering DAC............................................................................. 284.3 Power Dissipation in the Digital Part ........................................................................................ 31

    4.3.1 Switching Activity....................................................................................................... 314.3.2 Load Capacitance ........................................................................................................ 334.3.3 Gate Capacitance......................................................................................................... 334.3.4 Connectivity Capacitance............................................................................................ 374.3.5 Power Dissipation of an N-bit Decoder ...................................................................... 374.3.6 Total Power Dissipation in the Digital Part................................................................. 38

    4.4 Power Dissipation in the Analog Part........................................................................................ 394.4.1 Quantization Noise ...................................................................................................... 394.4.2 SNR for DACs ............................................................................................................ 404.4.3 Unit Current vs. Temperature...................................................................................... 414.4.4 Noise............................................................................................................................ 424.4.5 Total Power Dissipation in the Analog Part ................................................................ 43

    5 Summary ...................................................................................................................... 455.1 Total Power Dissipation............................................................................................................. 45

    5.1.1 Power Dissipation in the Digital Part .......................................................................... 455.1.2 Power Dissipation in the Analog Part ......................................................................... 45

    5.2 Conclusions................................................................................................................................45

  • 5.3 Further Work...............................................................................................................................46

    6 References .................................................................................................................... 47

    7 Appendix ...............................................................................................