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AD677BD 数据表(PDF) 8 Page - Analog Devices |
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AD677BD 数据表(HTML) 8 Page - Analog Devices |
8 / 17 page INTERMODULATION DISTORTION (IMD) With inputs consisting of sine waves at two frequencies, fa and fb, any device with nonlinearities will create distortion products, of order (m+n), at sum and difference frequencies of mfa ± nfb, where m, n = 0, 1, 2, 3 . . . . Intermodulation terms are those for which m or n is not equal to zero. For example, the second order terms are (fa + fb) and (fa – fb), and the third order terms are (2 fa + fb), (2 fa – fb), (fa + 2 fb) and (fa – 2 fb). The IMD products are expressed as the decibel ratio of the rms sum of the measured input signals to the rms sum of the distortion terms. The two signals applied to the converter are of equal amplitude, and the peak value of their sum is –0.5 dB from full scale. The IMD products are normalized to a 0 dB input signal. APERTURE DELAY Aperture delay is the time required after SAMPLE pin is taken LOW for the internal sample-hold of the AD677 to open, thus holding the value of VIN. APERTURE JITTER Aperture jitter is the variation in the aperture delay from sample to sample. POWER SUPPLY REJECTION DC variations in the power supply voltage will affect the overall transfer function of the ADC, resulting in zero error and full- scale error changes. Power supply rejection is the maximum change in either the bipolar zero error or full-scale error value. Additionally, there is another power supply variation to con- sider. AC ripple on the power supplies can couple noise into the ADC, resulting in degradation of dynamic performance. This is displayed in Figure 15. INPUT SETTLING TIME Settling time is a function of the SHA’s ability to track fast slewing signals. This is specified as the maximum time required in track mode after a full-scale step input to guarantee rated conversion accuracy. NOISE/DC CODE UNCERTAINTY Ideally, a fixed dc input should result in the same output code for repetitive conversions. However, as a consequence of un- avoidable circuit noise within the wideband circuits in the ADC, there is a range of output codes which may occur for a given in- put voltage. If you apply a dc signal to the ADC and record a large number of conversions, the result will be a distribution of codes. If you fit a Gaussian probability distribution to the histo- gram, the standard deviation is approximately equivalent to the rms input noise of the ADC. REV. A –7– Definition of Specifications–AD677 NYQUIST FREQUENCY An implication of the Nyquist sampling theorem, the “Nyquist frequency’’ of a converter is that input frequency which is one half the sampling frequency of the converter. TOTAL HARMONIC DISTORTION Total harmonic distortion (THD) is the ratio of the rms sum of the harmonic components to the rms value of a full-scale input signal and is expressed in percent (%) or decibels (dB). For in- put signals or harmonics that are above the Nyquist frequency, the aliased components are used. SIGNAL-TO-NOISE PLUS DISTORTION RATIO Signal-to-noise plus distortion is defined to be the ratio of the rms value of the measured input signal to the rms sum of all other spectral components below the Nyquist frequency, includ- ing harmonics but excluding dc. +/– FULL-SCALE ERROR The last + transition (from 011 . . . 10 to 011 . . . 11) should occur for an analog voltage 1.5 LSB below the nominal full scale (4.99977 volts for a ±5 V range). The full-scale error is the deviation of the actual level of the last transition from the ideal level. BIPOLAR ZERO ERROR Bipolar zero error is the difference between the ideal midscale input voltage (0 V) and the actual voltage producing the mid- scale output code. DIFFERENTIAL NONLINEARITY (DNL) In an ideal ADC, code transitions are one LSB apart. Differen- tial nonlinearity is the maximum deviation from this ideal value. It is often specified in terms of resolution for which no missing codes are guaranteed. INTEGRAL NONLINEARITY (INL) The ideal transfer function for an ADC is a straight line bisect- ing the center of each code drawn between “zero” and “full scale.” The point used as “zero” occurs 1/2 LSB before the most negative code transition. “Full scale” is defined as a level 1.5 LSB beyond the most positive code transition. Integral non- linearity is the worst-case deviation of a code center average from the straight line. BANDWIDTH The full-power bandwidth is that input frequency at which the amplitude of the reconstructed fundamental is reduced by 3 dB for a full-scale input. |
类似零件编号 - AD677BD |
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类似说明 - AD677BD |
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