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  • 參數(shù)資料
    型號: AD7899ARS-2
    英文描述: Analog-to-Digital Converter, 14-Bit
    中文描述: 模擬到數(shù)字轉(zhuǎn)換器,14位
    文件頁數(shù): 11/20頁
    文件大小: 191K
    代理商: AD7899ARS-2
    REV. B
    AD7890
    –11–
    When using the device in the External-Clocking Mode, the out-
    put register can be read at any time and the most up-to-date
    conversion result will be obtained. However, reading data from
    the output register or writing data to the Control Register dur-
    ing conversion or during the 500 ns prior to the next
    CONVST
    will result in reduced performance from the part. A read opera-
    tion to the output register has most effect on performance with
    the signal-to-noise ratio likely to degrade especially when higher
    serial clock rates are used while the code flicker from the part
    will also increase (see AD7890 Performance section).
    Figure 5 shows the timing and control sequence required to
    obtain optimum performance from the part in the external
    clocking mode. In the sequence shown, conversion is initiated
    on the rising edge of
    CONVST
    and new data is available in the
    output register of the AD7890 5.9
    μ
    s later. Once the read oper-
    ation has taken place, a further 500 ns should be allowed before
    TRACK/HOLD GOES
    INTO THE HOLD
    t
    CONVERT
    THREE-STATE
    NOTE:
    (I) SIGNIFIES AN INPUT; (O) SIGNIFIES AN OUTPUT. PULL-UP RESISTOR ON SCLK.
    DATA OUT (O)
    SCLK (O)
    RFS
    (O)
    CONVST
    (I)
    Figure 4. Self-Clocking (Master) Mode Conversion Sequence
    RFS
    TFS
    t
    CONVERT
    500ns MIN
    CONVST
    SCLK
    CONVERSION IS
    INITIATED AND
    TRACK/HOLD GOES
    INTO HOLD
    CONVERSION
    ENDS 5.9 s
    LATER
    SERIAL READ
    AND WRITE
    OPERATIONS
    READ AND WRITE
    OPERATIONS SHOULD END
    500ns PRIOR TO NEXT
    RISING EDGE OF
    CONVST
    NEXT CONVERSION
    START COMMAND
    Figure 5. External Clocking (Slave) Mode Timing Sequence for Optimum Performance
    the next rising edge of
    CONVST
    to optimize the settling of the
    track/hold before the next conversion is initiated. The diagram
    shows the read operation and the write operation taking place in
    parallel. On the sixth falling edge of SCLK in the write sequence
    the internal pulse will be initiated. Assuming MUX OUT is
    connected to SHA IN, 2
    μ
    s are required between this sixth
    falling edge of SCLK and the rising edge of
    CONVST
    to allow
    for the full acquisition time of the track/hold amplifier. With the
    serial clock rate at its maximum of 10 MHz, the achievable
    throughput rate for the part is 5.9
    μ
    s (conversion time) plus
    0.6
    μ
    s (six serial clock pulses before internal pulse is initiated)
    plus 2
    μ
    s (acquisition time). This results in a minimum through-
    put time of 8.5
    μ
    s (equivalent to a throughput rate of 117 kHz).
    If the part is operated with a slower serial clock, it will impact
    the achievable throughput rate for optimum performance.
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