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AD7856KR データシート(PDF) 8 Page - Analog Devices |
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AD7856KR データシート(HTML) 8 Page - Analog Devices |
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8 / 32 page  AD7856 –8– REV. A TERMINOLOGY 1 Integral Nonlinearity This is the maximum deviation from a straight line passing through the endpoints of the ADC transfer function. The end- points of the transfer function are zero scale, a point 1/2 LSB below the first code transition, and full scale, a point 1/2 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. Total Unadjusted Error This is the deviation of the actual code from the ideal code taking all errors into account (Gain, Offset, Integral Nonlinearity and other errors) at any point along the transfer function. Unipolar Offset Error This is the deviation of the first code transition (00 . . . 000 to 00 . . . 001) from the ideal AIN(+) voltage (AIN(–) + 1/2 LSB). Positive Full-Scale Error This is the deviation of the last code transition from the ideal AIN(+) voltage (AIN(–) + Full Scale – 1.5 LSB) after the offset error has been adjusted out. Channel-to-Channel Isolation Channel-to-channel isolation is a measure of crosstalk between the channels. It is measured by applying a full-scale 25 kHz signal to the other seven channels and determining how much that signal is attenuated in the channel of interest. The figure given is the worst case for all channels. Track/Hold Acquisition Time The track/hold amplifier returns into track mode and the end of conversion. Track/Hold acquisition time is the time required for the output of the track/hold amplifier to reach its final value, within ±1/2 LSB, after the end of conversion. 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 number of quantization levels in the digiti- zation process; the more levels, the smaller the quantization noise. The theoretical 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 14-bit converter, this is 86 dB. NOTE 1AIN(+) refers to the positive input of the pseudo-differential pair, and AIN(–) refers to the negative analog input of the pseudo-differential pair or to AGND depending on the channel configuration. Total Harmonic Distortion Total Harmonic Distortion (THD) is the ratio of the rms sum of harmonics to the fundamental. For the AD7856, it is defined as: THD (dB) = 20 log V 2 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 deter- mined by the largest harmonic in the spectrum, but for parts where the harmonics are buried in the noise floor, it will be a noise peak. 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 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). Testing is performed 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 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 fundamentals expressed in dBs. Full Power Bandwidth The Full Power Bandwidth (FPBW) of the AD7856 is that frequency at which the amplitude of the reconstructed (using FFTs) fundamental (neglecting harmonics and SNR) is reduced by 3 dB for a full-scale input. |
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同様の説明 - AD7856KR |
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