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AD7992 データシート(PDF) 10 Page - Analog Devices |
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AD7992 データシート(HTML) 10 Page - Analog Devices |
10 / 29 page AD7992 Rev. 0 | Page 9 of 28 TERMINOLOGY Signal-to-Noise and Distortion Ratio (SINAD) The measured ratio of signal-to-noise and distortion at the output of the A/D converter. 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 digit- ization process; the more levels, the smaller the quantization noise. The theoretical signal-to-noise and distortion ratio for an ideal N-bit converter with a sine wave input is given by Signal-to-(Noise + Distortion) = (6.02 N + 1.76) dB Thus, the SINAD is 74 dB for a 12-bit converter. Total Harmonic Distortion (THD) The ratio of the rms sum of harmonics to the fundamental. For the AD7992, it 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 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. Typically, 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, and so on. Intermodulation distortion terms are those for which neither m nor n equal zero. For example, second-order terms include (fa + fb) and (fa − fb), while third-order terms include (2fa + fb), (2fa − fb),(fa + 2fb), and (fa − 2fb). The AD7992 is 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. The calculation of intermodulation distortion is, like the THD specification, the ratio of the rms sum of the individual distortion products to the rms amplitude of the sum of the fundamentals, expressed in dB. Channel-to-Channel Isolation A measure of the level of crosstalk between channels, taken by applying a full-scale sine wave signal to the unselected input channels, and determining how much the 108 Hz signal is attenuated in the selected channel. The sine wave signal applied to the unselected channels is then varied from 1 kHz up to 2 MHz, each time determining how much the 108 Hz signal in the selected channel is attenuated. This figure represents the worst-case level across all channels. Aperture Delay The measured interval between the sampling clock’s leading edge and the point at which the ADC takes the sample. Aperture Jitter The sample-to-sample variation in the effective point in time when the sample is taken. Full-Power Bandwidth The input frequency at which the amplitude of the reconstructed fundamental is reduced by 0.1 dB or 3 dB for a full-scale input. Power Supply Rejection Ratio (PSRR) The ratio of the power in the ADC output at the full-scale frequency, f, to the power of a 200 mV p-p sine wave applied to the ADC VDD supply of frequency fS: PSRR (dB) = 10 log (Pf/PfS) where Pf is the power at frequency f in the ADC output; PfS is the power at frequency fS coupled onto the ADC VDD supply. Integral Nonlinearity The maximum deviation from a straight line passing through the endpoints of the ADC transfer function. The endpoints are zero scale, a point 1 LSB below the first code transition, and full scale, a point 1 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 + 1 LSB. Offset Error Match The difference in offset error between any two channels. Gain Error The deviation of the last code transition (111…110) to (111…111) from the ideal (that is, REFIN − 1 LSB) after the offset error has been adjusted out. Gain Error Match The difference in gain error between any two channels. |
同様の部品番号 - AD7992_15 |
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同様の説明 - AD7992_15 |
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