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AD668J データシート(PDF) 5 Page - Analog Devices |
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AD668J データシート(HTML) 5 Page - Analog Devices |
5 / 16 page 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 = IOUT × RLOAD (for both unipolar and bipolar modes) where: VIN – the analog input voltage. VNOM – 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. RLOAD – the resistance of the DAC output node; the maximum this can be is 200 Ω (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 Ω ( ±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; VOUT is still just IOUT × RLOAD) where: OFFSETANALOG = the analog offset error. OFFSETDIGITAL = is the unipolar digital offset error. OFFSETBIPOLAR = is the bipolar offset error. E = the gain error, expressed fractionally. Operating Limits: |
同様の部品番号 - AD668J |
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同様の説明 - AD668J |
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