• 參數(shù)資料
    型號(hào)： LTC1967
    廠商： Linear Integrated Systems
    英文描述： Precision Extended Bandwidth, RMS-to-DC Converter
    中文描述： 精密擴(kuò)展帶寬，有效值- DC轉(zhuǎn)換器
    文件頁(yè)數(shù)： 9/28頁(yè)
    文件大小： 328K
    代理商： LTC1967
    9
    LTC1967
    1967f
    APPLICATIOU
    W
    U
    U
    Note that the internal scalings are such that the
    Σ
    output
    duty cycle is limited to 0% or 100% only when V
    IN
    exceeds
    ±
    4 V
    OUT
    .
    Linearity of an RMS-to-DC Converter
    Linearity may seem like an odd property for a device that
    implements a function that includes two very nonlinear
    processes: squaring and square rooting.
    However, an RMS-to-DC converter has a transfer func-
    tion, RMS volts in to DC volts out, that should ideally have
    a 1:1 transfer function. To the extent that the input to
    output transfer function does not lie on a straight line, the
    part is nonlinear.
    A more complete look at linearity uses the simple model
    shown in Figure 5. Here an ideal RMS core is corrupted by
    both input circuitry and output circuitry that have imper-
    fect transfer functions. As noted, input offset is introduced
    in the input circuitry, while output offset is introduced in
    the output circuitry.
    Any nonlinearity that occurs in the output circuity will
    corrupt the RMS in to DC out transfer function. A nonlin-
    earity in the input circuitry will typically corrupt that
    transfer function far less simply because with an AC input,
    the RMS-to-DC conversion will average the nonlinearity
    from a whole range of input values together.
    But the input nonlinearity will still cause problems in an
    RMS-to-DC converter because it will corrupt the accuracy
    as the input signal shape changes. Although an RMS-to-
    DC converter will convert any input waveform to a DC
    output, the accuracy is not necessarily as good for all
    waveforms as it is with sine waves. A common way to
    describe dynamic signal wave shapes is Crest Factor. The
    crest factor is the ratio of the peak value relative to the RMS
    value of a waveform. A signal with a crest factor of 4, for
    instance, has a peak that is four times its RMS value.
    The
    Σ
    modulator has a single-bit output whose average
    duty cycle (D) will be proportional to the ratio of the input
    signal divided by the output. The
    Σ
    is a 2nd order
    modulator with excellent linearity. The single-bit output is
    used to selectively buffer or invert the input signal. Again,
    this is a circuit with excellent linearity, because it operates
    at only two points:
    ±
    1 gain; the average effective multipli-
    cation over time will be on the straight line between these
    two points. The combination of these two elements again
    creates a lowpass filter input signal equal to (V
    IN
    )
    2
    /V
    OUT
    ,
    which, as shown above, results in RMS-to-DC conversion.
    The lowpass filter performs the averaging of the RMS
    function and must be a lower corner frequency than the
    lowest frequency of interest. For line frequency measure-
    ments, this filter is simply too large to implement on-chip,
    but the LTC1967 needs only one capacitor on the output
    to implement the lowpass filter. The user can select this
    capacitor depending on frequency range and settling time
    requirements, as will be covered in the Design Cookbook
    section to follow.
    This topology is inherently more stable and linear than log/
    antilog implementations primarily because all of the signal
    processing occurs in circuits with high gain op amps
    operating closed loop.
    More detail of the LTC1967 inner workings is shown in the
    Simplified Schematic towards the end of this data sheet.
    Figure 4. Topology of LTC1967
    -
    Σ
    REF
    V
    IN
    V
    OUT
    LPF
    1967 F04
    ±
    1
    D
    V
    V
    IN
    OUT
    α
    INPUT CIRCUITRY
    V
    IOS
    INPUT NONLINEARITY
    IDEAL
    RMS-TO-DC
    CONVERTER
    OUTPUT CIRCUITRY
    V
    OOS
    OUTPUT NONLINEARITY
    INPUT
    OUTPUT
    1967 F05
    Figure 5. Linearity Model of an RMS-to-DC Converter
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    相關(guān)代理商/技術(shù)參數(shù)
    參數(shù)描述
    LTC1967CMS8 功能描述:IC CONVERTER RMS-DC PREC 8MSOP RoHS:否 類別:集成電路 (IC) >> PMIC - RMS 至 DC 轉(zhuǎn)換器 系列:- 標(biāo)準(zhǔn)包裝:46 系列:- 電流 - 電源:1.2mA 電源電壓:±18 V，36 V 安裝類型:表面貼裝 封裝/外殼:16-SOIC（0.295"，7.50mm 寬） 供應(yīng)商設(shè)備封裝:16-SOIC W 包裝:管件
    LTC1967CMS8#PBF 功能描述:IC CONVERTER RMS-DC PREC 8MSOP RoHS:否 類別:集成電路 (IC) >> PMIC - RMS 至 DC 轉(zhuǎn)換器 系列:- 標(biāo)準(zhǔn)包裝:46 系列:- 電流 - 電源:1.2mA 電源電壓:±18 V，36 V 安裝類型:表面貼裝 封裝/外殼:16-SOIC（0.295"，7.50mm 寬） 供應(yīng)商設(shè)備封裝:16-SOIC W 包裝:管件
    LTC1967CMS8#TR 功能描述:IC CONVERTER RMS-DC PREC 8MSOP RoHS:否 類別:集成電路 (IC) >> PMIC - RMS 至 DC 轉(zhuǎn)換器 系列:- 標(biāo)準(zhǔn)包裝:46 系列:- 電流 - 電源:1.2mA 電源電壓:±18 V，36 V 安裝類型:表面貼裝 封裝/外殼:16-SOIC（0.295"，7.50mm 寬） 供應(yīng)商設(shè)備封裝:16-SOIC W 包裝:管件
    LTC1967CMS8#TRPBF 功能描述:IC CONVERTER RMS-DC PREC 8MSOP RoHS:是 類別:集成電路 (IC) >> PMIC - RMS 至 DC 轉(zhuǎn)換器 系列:- 標(biāo)準(zhǔn)包裝:46 系列:- 電流 - 電源:1.2mA 電源電壓:±18 V，36 V 安裝類型:表面貼裝 封裝/外殼:16-SOIC（0.295"，7.50mm 寬） 供應(yīng)商設(shè)備封裝:16-SOIC W 包裝:管件
    LTC1967CMS8PBF 制造商:Linear Technology 功能描述:RMS-DC converter, LTC1967 40kHz MSOP
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