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AD7457BRT-REEL7 数据表(PDF) 10 Page - Analog Devices |
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AD7457BRT-REEL7 数据表(HTML) 10 Page - Analog Devices |
10 / 20 page AD7457 Rev. A | Page 10 of 20 TERMINOLOGY Signal to (Noise + Distortion) Ratio (SINAD) The measured ratio of SINAD at the output of the 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 Therefore, 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 AD7457, it is defined as () 1 2 6 2 5 2 4 2 3 2 2 20 dB V V V V V V log THD + + + + = where: V1 is the rms amplitude of the fundamental. V2 , V3, V4, V5, and V6 are the rms amplitudes of the second to 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 specifica- tion 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 prod- ucts 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 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). The AD7457 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 fre- quency 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 the intermodulation distortion is as per the total harmonic distortion specification, where it is the ratio of the rms sum of the individual distortion products to the rms amplitude of the sum of the fundamentals expressed in dB. Aperture Delay The amount of time from the leading edge of the sampling clock until the ADC actually takes the sample. Aperture Jitter The sample-to-sample variation in the effective point in time at which the actual sample is taken. Full-Power Bandwidth The full-power bandwidth of an ADC is that input frequency at which the amplitude of the reconstructed fundamental is reduced by 0.1 dB or 3 dB for a full-scale input. Integral Nonlinearity (INL) The maximum deviation from a straight line passing through the endpoints of the ADC transfer function. Differential Nonlinearity (DNL) 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 (000...000 to 000...001) from the ideal (that is, AGND + 1 LSB). Gain Error The deviation of the last code transition (111...110 to 111...111) from the ideal (that is, VREF − 1 LSB), after the offset error has been adjusted out. Track-and-Hold Acquisition Time 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. Power Supply Rejection Ratio (PSRR) The ratio of the power in the ADC output at full-scale frequency, f, to the power of a 100 mV p-p sine wave applied to the ADC VDD supply of frequency fs. The frequency of this input varies from 1 kHz to 1 MHz. PSRR (dB) = 10 log(Pf/Pfs) Pf is the power at frequency f in the ADC output; Pfs is the power at frequency fs in the ADC output. |
类似零件编号 - AD7457BRT-REEL7 |
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类似说明 - AD7457BRT-REEL7 |
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