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AD7495ARZ データシート(PDF) 11 Page - Analog Devices |
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AD7495ARZ データシート(HTML) 11 Page - Analog Devices |
11 / 24 page AD7475/AD7495 Rev. B | Page 11 of 24 ) TERMINOLOGY Integral Nonlinearity The maximum deviation from a straight line passing through the endpoints of the ADC transfer function. The endpoints of the transfer function are zero scale, a point ½ LSB below the first code transition, and full scale, a point ½ LSB above the last code transition. Differential Nonlinearity The difference between the measured and the ideal 1 LSB change between any two adjacent codes in the ADC. Offset Error The deviation of the first code transition (00 . . . 000) to (00 . . . 001) from the ideal, that is, AGND + 0.5 LSB. Gain Error This is the deviation of the last code transition (111. . . 110) to (111. . . 111) from the ideal (that is, VREF − 1.5 LSB) after the offset error has been adjusted out. Track-and-Hold Acquisition Time The track-and-hold amplifier returns into track mode on the 13 th SCLK rising edge (see the Serial Interface section). The track-and-hold acquisition time is the minimum time required for the track-and-hold amplifier to remain in track mode for its output to reach and settle to within 0.5 LSB of the applied input signal, given a step change to the input signal. Signal-to-Noise and Distortion Ratio (SINAD) The measured ratio of signal-to-noise and distortion at the output of the analog-to-digital converter (ADC). The signal is the rms amplitude of the fundamental. Noise is the sum of all nonfundamental signals up to half the sampling frequency (fS/2), excluding dc. The ratio is dependent on the number of quantization levels in the digitization process; the more levels, the smaller the quantization noise. The theoretical SINAD ratio for an ideal N-bit converter with a sine wave input is given by () ( dB 76 . 1 02 . 6 + = + N Distortion Noise to Signal For a 12-bit converter, the SINAD is 74 dB. Total Harmonic Distortion (THD) The ratio of the rms sum of harmonics to the fundamental. For the AD7475/AD7495, THD is defined as () 1 6 5 4 3 2 V V V V V V THD 2 2 2 2 2 log 20 dB + + + + = 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 harmonics. Peak Harmonic or Spurious Noise 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 determined by the largest harmonic in the spectrum, but for ADCs where the harmonics are buried in the noise floor, it is a noise peak. 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, etc. Intermodulation distortion terms are those for which neither m nor n is 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). The AD7475/AD7495 are tested using the CCIF standard where two input frequencies near the top end of the input bandwidth are used. In this case, 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. Like THD, intermodulation distortion is calculated as the rms sum of the individual distortion products to the rms amplitude of the sum of the fundamentals, expressed in dBs. |
同様の部品番号 - AD7495ARZ |
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同様の説明 - AD7495ARZ |
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