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AD7994BRU-0 データシート(PDF) 10 Page - Analog Devices |
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AD7994BRU-0 データシート(HTML) 10 Page - Analog Devices |
10 / 27 page AD7994/AD7993 –10– REV. PrF PRELIMINARYTECHNICAL DATA Channel-to-Channel Isolation Channel-to-Channel Isolation is a measure of the level of crosstalk between channels. It is measured by applying a fullscale TBD kHz sine wave signal to the nonselected input channels and determining how much the TBD kHz signal is attenuated in the selected channel. This figure is given worse case across all channels. Aperture Delay This is the measured interval between the leading edge of the sampling clock and the point at which the ADC actu- ally takes the sample. Aperture Jitter This is the sample-to-sample variation in the effective point in time at which the sample is taken. Full Power Bandwidth The Full Power Bandwidth of an ADC is that input fre- quency at which the amplitude of the reconstructed Fun- damental is reduced by 0.1 dB or 3 dB for a full-scale input PSRR (Power Supply Rejection) The power supply rejection ratio is defined as the ratio of the power in the ADC output at 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) Pf is the power at frequency f in the ADC output; Pfs is the power at frequency fs coupled into the ADC VDD sup- ply. Integral Nonlinearity This is the maximum deviation from a straight line pass- ing through the endpoints of the ADC transfer function. The endpoints of the transfer function 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 This is the difference between the measured and the ideal 1 LSB change between any two adjacent codes in the ADC. Offset Error This is the deviation of the first code transition (00 . . . 000) to (00 . . . 001) from the ideal, i.e AGND + 1LSB Offset Error Match This is the difference in offset error between any two channels. Gain Error This is the deviation of the last code transition (111 . . . 110) to (111 . . . 111) from the ideal (i.e., REFIN – 1 LSB) after the offset error has been adjusted out. Gain Error Match This is the difference in Gain error between any two chan- nels. TERMINOLOGY Signal to (Noise + Distortion) Ratio This is the measured ratio of signal to (noise + 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 num- ber of quantization levels in the digitization process; the more levels, the smaller the quantization noise. The theo- retical signal to (noise + 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 for a 12-bit converter, this is 74 dB Total Harmonic Distortion Total harmonic distortion (THD) is the ratio of the rms sum of harmonics to the fundamental. For the AD7994/ AD7993, it is defined as: THD (dB ) = 20 log V2 2 +V 3 2 +V 4 2 +V 5 2 +V 6 2 V1 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 Peak harmonic or spurious noise is defined as 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 har- monic in the spectrum, but for ADCs where the har- monics are buried in the noise floor, it will be a noise peak. Intermodulation Distortion With inputs consisting of sine waves at two frequen- cies, 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 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 AD7994/AD7993 is tested using the CCIF stan- dard 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 speci- fied separately. The calculation of the intermodulation distortion is as per the THD specification where it is the ratio of the rms sum of the individual distortion products to the rms amplitude of the sum of the funda- mentals expressed in dBs. |
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