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AD7720 Datasheet(PDF) 8 Page - Analog Devices |
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AD7720 Datasheet(HTML) 8 Page - Analog Devices |
8 / 17 page AD7720 –7– REV. 0 TERMINOLOGY (IDEAL FIR FILTER USED WITH AD7720 [FIGURE 1]) Integral Nonlinearity This is the maximum deviation of any code from a straight line passing through the endpoints of the transfer function. The endpoints of the transfer function are zero scale (not to be con- fused with bipolar zero), a point 0.5 LSB below the first code transition (100...00 to 100...01 in bipolar mode and 000...00 to 000...01 in unipolar mode) and full scale, a point 0.5 LSB above the last code transition (011...10 to 011...11 in bipolar mode and 111...10 to 111...11 in unipolar mode). The error is expressed in LSBs. Differential Nonlinearity This is the difference between the measured and the ideal 1 LSB change between two adjacent codes in the ADC. Common-Mode Rejection Ratio The ability of a device to reject the effect of a voltage applied to both input terminals simultaneously—often through variation of a ground level—is specified as a common-mode rejection ratio. CMRR is the ratio of gain for the differential signal to the gain for the common-mode signal. Unipolar Offset Error Unipolar offset error is the deviation of the first code transition from the ideal VIN(+) voltage which is (VIN(–) + 0.5 LSB) when operating in the unipolar mode. Bipolar Offset Error This is the deviation of the midscale transition (111...11 to 000... 00) from the ideal VIN(+) voltage which is (VIN(–) –0.5 LSB) when operating in the bipolar mode. Gain Error The first code transition should occur at an analog value 1/2 LSB above minus full scale. The last code transition should occur for an analog value 3/2 LSB below the nominal full scale. Gain error is the deviation of the actual difference between first and last code transitions and the ideal difference between first and last code transitions. Signal-to-(Noise + Distortion) Signal-to-(Noise + Distortion) is measured signal-to-noise at the output of the ADC. The signal is the rms magnitude of the fundamental. Noise plus distortion is the rms sum of all of the nonfundamental signals and harmonics to half the output word rate (fMCLK/128), excluding dc. Signal-to-(Noise + Distortion) is dependent on the number of quantization levels used in the digitization process; the more levels, the smaller the quantiza- tion noise. The theoretical Signal-to-(Noise + Distortion) ratio for a sine wave input is given by Signal-to-(Noise + Distortion) = (6.02 N + 1.76) dB where N is the number of bits. Total Harmonic Distortion Total Harmonic Distortion (THD) is the ratio of the rms sum of harmonics to the rms value of the fundamental. For the AD7720, THD is defined as THD = 20 log (V 2 2 +V 3 2 +V 4 2 +V 5 2 +V 6 2) V 1 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. Spurious Free Dynamic Range Spurious free dynamic range is the difference, in dB, between the peak spurious or harmonic component in the ADC output spectrum (up to fMCLK/128 and excluding dc) and the rms value of the fundamental. Normally, the value of this specification will be determined by the largest harmonic in the output spectrum of the FFT. For input signals whose second harmonics occur in the stop band region of the digital filter, a spur in the noise floor limits the spurious free dynamic range. Intermodulation Distortion With inputs consisting of sine waves at two frequencies, fa and fb, any active device with nonlinearities will create distortion products at sum and difference frequencies of mfa ± nfb where m, n = 0, 1, 2, 3, etc. Intermodulation distortion terms are those for which neither m or 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). |
Número de pieza similar - AD7720_17 |
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Descripción similar - AD7720_17 |
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