參數(shù)資料
      型號(hào): AD668AQ
      廠商: ANALOG DEVICES INC
      元件分類: DAC
      英文描述: 12-Bit Ultrahigh Speed Multiplying D/A Converter
      中文描述: PARALLEL, WORD INPUT LOADING, 0.12 us SETTLING TIME, 12-BIT DAC, CDIP24
      封裝: 0.300 INCH, SKINNY, CERDIP-24
      文件頁數(shù): 5/16頁
      文件大小: 602K
      代理商: AD668AQ
      AD668
      REV. A
      –5–
      ANALOG OFFSET ERROR: The analog offset is defined as
      the offset of the analog amplifier channel, referred to the analog
      input. Ideally, this would be measured with the analog input at
      0 V and the digital input at full scale. Since a 0 V analog input
      voltage constitutes an undervoltage condition, this specification
      is determined through linear extrapolation, as indicated in
      Figure 1.
      Figure 1. Derivation of Analog Offset Voltage
      GLITCH IMPULSE: Asymmetrical switching times in a DAC
      may give rise to undesired output transients which are quanti-
      fied by their glitch impulse. It is specified as the net area of the
      glitch in pV-sec.
      Figure 2. AD668 Major Carry Glitch
      FUNCTIONAL DESCRIPTION
      The AD668 is designed to combine excellent performance with
      maximum flexibility. The functional block diagram and the
      simple transfer functions provided below will provide the user
      with a basic grasp of the AD668’s operation. Examples of typi-
      cal circuit configurations are provided in the section APPLY-
      ING THE AD668. Subsequent sections contain more detailed
      information useful in optimizing DAC performance in high
      speed, high resolution applications.
      DAC Transfer Function
      The AD668 may be used either in a current output mode (DAC
      output connected to a virtual ground) or a voltage output mode
      (DAC output connected to a resistive load).
      In current output mode:
      Unipolar Mode
      I
      OUT
      =
      V
      IN
      V
      NOM
      ×
      DAC code
      4096
      ×
      10.24
      mA
      Bipolar Mode
      I
      OUT
      =
      V
      IN
      V
      NOM
      ×
      DAC code
      4096
      ×
      10.24
      mA
      V
      IN
      V
      NOM
      ×
      5.12
      mA
      In voltage output mode:
      V
      OUT
      =
      I
      OUT
      ×
      R
      LOAD
      (for both unipolar and bipolar modes)
      where:
      V
      IN
      – the analog input voltage.
      V
      NOM
      the nominal full scale of the reference voltage: 1 V,
      1.25 V, or 5 V, determined by the wiring configuration of Pins
      21 and 22. (See APPLYING THE AD668.)
      DAC code –
      the numerical representation of the DAC’s digital
      inputs; a number between 0 and 4095.
      R
      LOAD
      the resistance of the DAC output node; the maximum
      this can be is 200
      (the internal DAC ladder resistance). The
      on-board load resistor (Pin 19) has been trimmed so that its
      parallel combination with the DAC ladder resistance is 100
      (
      ±
      1%)
      Bipolar mode –
      produces a bipolar analog output from the digital
      input by offsetting the normal output current with a precision
      current source. This offset is achieved by connecting Pin 16 to
      the DAC output. In the unipolar mode, Pin 16 should be
      grounded.
      If the dc errors are included, the transfer function becomes
      somewhat more complex:
      I
      OUT
      =
      V
      IN
      V
      NOM
      +
      OFFSET
      ANALOG
      ×
      DAC code
      4096
      ×
      (1
      +
      E
      )
      ×
      10.24
      mA
      +
      OFFSET
      DIGITAL
      ×
      V
      IN
      V
      NOM
      ×
      10.24
      mA
      V
      IN
      V
      NOM
      +
      OFFSET
      ANALOG
      ×
      (5.12
      mA
      +
      [
      OFFSET
      BIPOLAR
      ×
      10.24
      mA
      ])
      (Last term is for use in bipolar mode; V
      OUT
      is still just I
      OUT
      ×
      R
      LOAD
      )
      where:
      OFFSET
      ANALOG
      =
      the analog offset error.
      OFFSET
      DIGITAL
      = is
      the unipolar digital offset error.
      OFFSET
      BIPOLAR
      = is
      the bipolar offset error.
      E
      = the gain error, expressed fractionally.
      Operating Limits:
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