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    參數(shù)資料
    型號(hào): AD7876BNZ
    廠商: Analog Devices Inc
    文件頁(yè)數(shù): 9/28頁(yè)
    文件大?。?/td> 0K
    描述: IC ADC 12BIT SAMPLING 10V 24DIP
    產(chǎn)品變化通告: Conversion Time Change
    標(biāo)準(zhǔn)包裝: 15
    位數(shù): 12
    采樣率(每秒): 100k
    數(shù)據(jù)接口: 串行,并聯(lián)
    轉(zhuǎn)換器數(shù)目: 1
    功率耗散(最大): 95mW
    電壓電源: 雙 ±
    工作溫度: -40°C ~ 85°C
    安裝類型: 通孔
    封裝/外殼: 24-DIP(0.300",7.62mm)
    供應(yīng)商設(shè)備封裝: 24-PDIP
    包裝: 管件
    輸入數(shù)目和類型: 1 個(gè)單端,雙極
    AD7870/AD7875/AD7876
    Rev. C | Page 17 of
    28
    Fourier transform (FFT) plot is generated from which the SNR
    data can be obtained. Figure 18 shows a typical 2048 point FFT
    plot of the AD7870KN/AD7875KN with an input signal of 25 kHz
    and a sampling frequency of 100 kHz. The SNR obtained from
    this graph is 72.6 dB. It should be noted that the harmonics are
    taken into account when calculating the SNR.
    0
    –30
    –60
    –90
    –120
    –140
    0
    25
    50
    07
    73
    0-
    0
    18
    S
    IG
    N
    AL
    AM
    P
    L
    IT
    UDE
    (
    d
    B)
    FREQUENCY (kHz)
    INPUT FREQUENCY = 25kHz
    SAMPLE FREQUENCY = 100kHz
    SNR = 72.6dB
    TA = 25°C
    Figure 18. FFT Plot
    Effective Number of Bits
    The formula given in Equation 1 relates SNR to the number of
    bits. Rewriting the formula, as in Equation 2, it is possible to get
    a measure of performance expressed in effective number of
    bits (N).
    02
    .
    6
    76
    .
    1
    =
    SNR
    N
    (2)
    The effective number of bits for a device can be calculated
    directly from its measured SNR.
    Figure 19 shows a typical plot of effective number of bits vs.
    frequency for an AD7870KN/AD7875KN with a sampling
    frequency of 100 kHz. The effective number of bits typically
    falls between 11.7 and 11.85 corresponding to SNR figures of
    72.2 and 73.1 dB.
    12.0
    11.5
    11.0
    10.5
    10.0
    0
    12.5
    18.75
    6.25
    25.0
    31.25
    37.5
    43.75
    50.0
    07
    73
    0-
    01
    9
    E
    F
    E
    CT
    IV
    E
    NUM
    BE
    R
    O
    F
    BI
    T
    S
    INPUT FREQUENCY (kHz)
    SAMPLE FREQUENCY = 100kHz
    TA = 25°C
    Figure 19. Effective Number of Bits vs. Frequency
    Total Harmonic Distortion (THD)
    THD is the ratio of the rms sum of harmonics to the rms
    value of the fundamental. For the AD7870/AD7875, THD is
    defined as
    1
    2
    6
    2
    5
    2
    4
    2
    3
    2
    log
    20
    V
    THD
    +
    =
    where V1 is the rms amplitude of the fundamental and V2, V3,
    V4, V5 and V6 are the rms amplitudes of the second through the
    sixth harmonic. The THD is also derived from the FFT plot of
    the ADC output spectrum.
    Intermodulation Distortion
    With inputs consisting of sine waves at two frequencies, fa and
    fb, any active device with nonlinearities creates distortion
    products at sum and difference frequencies of mfa ± nfb where
    m, n = 0, 1, 2, 3, and so on. Intermodulation terms are those
    for which neither m nor n are equal to zero. For example, the
    second order terms include (fa + fb) and (fa fb), while the
    third order terms include (2fa + fb), (2fa fb), (fa + 2fb) and
    (fa 2fb).
    Using the CCIF standard, where two input frequencies near the
    top end of the input bandwidth are used, the second and third
    order terms are of different significance. The second order
    terms are usually distanced in frequency from the original sine
    waves while the third order terms are usually at a frequency
    close to the input frequencies. As a result, the second and third
    order terms are specified separately. The calculation of the
    intermodulation distortion is as per the THD specification
    where it is the ratio of the rms sum of the individual distortion
    products to the rms amplitude of the fundamental expressed in
    dBs. In this case, the input consists of two, equal amplitude, low
    distortion sine waves. Figure 20 shows a typical IMD plot for
    the AD7870/AD7875.
    Peak Harmonic or Spurious Noise
    Peak harmonic or spurious noise is defined as the ratio of the
    rms value of the next largest component in the ADC output
    spectrum (up to FS/2 and excluding dc) to the rms value of the
    fundamental. Normally, the value of this specification is deter-
    mined by the largest harmonic in the spectrum, but for parts
    where the harmonics are buried in the noise floor the peak is a
    noise peak.
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    相關(guān)代理商/技術(shù)參數(shù)
    參數(shù)描述
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