• Sigma- C haracteristic Flash Pipelined SAR Delta
  • Total Throughput Effective




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    analog-to-digital-converter-architectures-and-choices

    Total
    Throughput Effective
    Converters
    (14-Bit
    Multiplexed Needed for
    Converter Architecture Resolution) Throughput Application
    AD7865
    SAR
    416 kSPS
    416 kSPS
    8
    AD7722
    Sigma-Delta
    220 kSPS
    2.3 kSPS
    16
    AD9240
    Pipelined
    10 MSPS
    10 MSPS
    1
    Of the three converters, only the AD9240 has the throughput
    needed to convert all 16 channels. The AD7865 has sufficient
    throughput for 2 inputs per converter. To use the AD7865 in this
    application, 8 converters would be needed. The AD7722 would


    4
    Analog Dialogue 33-8 (1999)
    need to be used in a converter-per-channel implementation; thus
    16 converters would be required.
    Summary
    While not exhaustive, the following table summarizes and ranks
    (in a generalized sense) the relative advantages of flash, pipelined,
    SAR, and sigma-delta architectures. A rank of 1 in a performance
    category indicates that the architecture is inherently better than
    the others for that category. An * indicates that the architecture
    has the capability or characteristic listed.
    Sigma-
    C
    haracteristic
    Flash Pipelined SAR Delta
    Throughput
    1
    2
    3
    4
    Resolution (ENOB)
    4
    3
    2
    1
    Latency
    1
    3
    2
    4
    Suitability for converting multiple
    signals per ADC
    1
    2
    1
    3
    Capability to convert non-periodic
    multiplexed signals
    1
    2
    1
    3
    Simplified anti-aliasing
    *
    Can undersample
    *
    *
    *
    Can increase resolution through
    averaging (with dither noise)
    *
    *
    *
    ACKNOWLEDGMENT
    The author is indebted to Alain Guery and Mike Coln for providing
    valuable direction, and for providing the figures shown.
    REFERENCES
    Analog-Digital Conversion Handbook
    , The Engineering Staff
    of Analog Devices, Inc. Englewood Cliffs, NJ: Prentice Hall,
    1986. ISBN 0-13-032848-0. Available from Analog Devices:
    Phone (781) 461-3392.
    Practical Analog Design Techniques
    , edited by Walt Kester. Norwood,
    MA: Analog Devices, Inc., 1995. ISBN 0-916550-16-8. Available
    from Analog Devices: Phone (781) 461-3392. Also available free
    on the Internet as 
    PDF chapters
    . http://www.analog.com/support/
    standard_linear/seminar_material/index.html
    High Speed Design Techniques
    , edited by Walt Kester. Norwood, MA:
    Analog Devices, Inc., 1996. ISBN 0-916550-17-6. Available from
    Analog Devices: Phone (781) 461-3392. Also available free on the
    Internet as 
    PDF chapters
    . http://www.analog.com/support/
    standard_linear/seminar_material/index.html
    Linear Design Seminar
    , edited by Walt Kester. Norwood, MA:
    Analog Devices, Inc., 1995. ISBN 0-916550-15-X. Available from
    Analog Devices: Phone (781) 461-3392.
    b

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