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AD7490BRU датащи(PDF) 7 Page - Analog Devices |
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AD7490BRU датащи(HTML) 7 Page - Analog Devices |
7 / 24 page AD7490 –7– REV. A TERMINOLOGY Integral Nonlinearity This is 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 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 1 LSB. 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 1LSB) after the offset error has been adjusted out. Gain Error Match This is the difference in gain error between any two channels. Zero Code Error This applies when using the twos complement output coding option, in particular to the 2 REFIN input range with –REFIN to +REFIN biased about the REFIN point. It is the deviation of the midscale transition (all 0s to all 1s) from the ideal VIN voltage, i.e., REFIN – 1 LSB. Zero Code Error Match This is the difference in zero code error between any two channels. Positive Gain Error This applies when using the twos complement output coding option, in particular to the 2 REFIN input range with –REFIN to +REFIN biased about the REFIN point. It is the deviation of the last code transition (011…110) to (011…111) from the ideal (i.e., +REFIN 1 LSB) after the Zero Code Error has been adjusted out. Positive Gain Error Match This is the difference in Positive Gain Error between any two channels. Negative Gain Error This applies when using the twos complement output coding option, in particular to the 2 REFIN input range with –REFIN to +REFIN biased about the REFIN point. It is the deviation of the first code transition (100…000) to (100…001) from the ideal (i.e., –REFIN + 1 LSB) after the Zero Code Error has been adjusted out. Negative Gain Error Match This is the difference in negative gain error between any two channels. Channel-to-Channel Isolation Channel-to-channel isolation is a measure of the level of cross- talk between channels. It is measured by applying a full-scale 400 kHz sine wave signal to all 15 nonselected input channels and determining how much that signal is attenuated in the selected channel with a 50 kHz signal. The figure is given worst case across all 16 channels for the AD7490. PSR (Power Supply Rejection) Variations in power supply will affect the full scale transition, but not the converter’s linearity. Power supply rejection is the maximum change in full-scale transition point due to a change in power- supply voltage from the nominal value. (See Typical Performance Characteristics.) Track/Hold Acquisition Time The track/hold amplifier returns into track on the 14th SCLK falling edge. Track/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 ±1 LSB of the applied input signal, given a step change to the input signal. 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 digitiza- tion 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 N dB () ( . . ) += + 602 176 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 AD7490, it is defined as: THD dB VVV V V V () log =× ++ + + 20 2 2 3 2 4 2 5 2 6 2 1 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 harmonic 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 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, 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 AD7490 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 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. |
Аналогичный номер детали - AD7490BRU |
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Аналогичное описание - AD7490BRU |
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