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AD7569TQ2 датащи(PDF) 5 Page - Analog Devices |
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AD7569TQ2 датащи(HTML) 5 Page - Analog Devices |
5 / 20 page AD7569/AD7669 –5– REV. B NOTE: The term DAC (Digital-to-Analog Converter) throughout the data sheet applies equally to the dual DACs in the AD7669 as well as to the single DAC of the AD7569 unless otherwise stated. It follows that the term VOUT applies to both VOUTA and VOUTB of the AD7669 also. TERMINOLOGY Total Unadjusted Error Total unadjusted error is a comprehensive specification that in- cludes internal voltage reference error, relative accuracy, gain and offset errors. Relative Accuracy (DAC) Relative Accuracy or endpoint nonlinearity is a measure of the maximum deviation from a straight line passing through the endpoints of the DAC transfer function. It is measured after al- lowing for offset and gain errors. For the bipolar output ranges, the endpoints of the DAC transfer function are defined as those voltages that correspond to negative full-scale and positive full- scale codes. For the unipolar output ranges, the endpoints are code 1 and code 255. Code 1 is chosen because the amplifier is now working in single supply and, in cases where the true offset of the amplifier is negative, it cannot be seen at code 0. If the relative accuracy were calculated between code 0 and code 255, the “negative offset” would appear as a linearity error. If the off- set is negative and less than 1 LSB, it will appear at code 1, and hence the true linearity of the converter is seen between code 1 and code 255. Relative Accuracy (ADC) Relative Accuracy is the deviation of the ADC’s actual code transition points from a straight line drawn between the end- points of the ADC transfer function. For the bipolar input ranges, these points are the measured, negative, full-scale transi- tion point and the measured, positive, full-scale transition point. For the unipolar ranges, the straight line is drawn between the measured first LSB transition point and the measured full-scale transition point. Differential Nonlinearity Differential Nonlinearity is the difference between the measured change and an ideal 1 LSB change between any two adjacent codes. A specified differential nonlinearity of ±1 LSB max en- sures monotonicity (DAC) or no missed codes (ADC). A differ- ential nonlinearity of ±3/4 LSB max ensures that the minimum step size (DAC) or code width (ADC) is 1/4 LSB, and the maxi- mum step size or code width is 3/4 LSB. Digital-to-Analog Glitch Impulse Digital-to-Analog Glitch Impulse is the impulse injected into the analog output when the digital inputs change state with the DAC selected. It is normally specified as the area of the glitch in nV secs and is measured when the digital input code is changed by 1 LSB at the major carry transition. Digital Feedthrough Digital Feedthrough is also a measure of the impulse injected to the analog output from the digital inputs, but is measured when the DAC is not selected. It is essentially feedthrough across the die and package. It is also a measure of the glitch impulse trans- ferred to the analog output when data is read from the internal ADC. It is specified in nV secs and is measured with WR high and a digital code change from all 0s to all 1s. DAC-to-DAC Crosstalk (AD7669 Only) The glitch energy transferred to the output of one DAC due to an update at the output of the second DAC. The figure given is the worst case and is expressed in nV secs. It is measured with an update voltage of full scale. DAC-to-DAC Isolation (AD7669 Only) DAC-to-DAC Isolation is the proportion of a digitized sine wave from the output of one DAC, which appears at the output of the second DAC (loaded with all 1s). The figure given is the worst case for the second DAC output and is expressed as a ra- tio in dBs. It is measured with a digitized sine wave (fSAMPLING = 100 kHz) of 20 kHz at 2.5 V pk-pk. Signal-to-Noise Ratio Signal-to-Noise Ratio (SNR) is the measured signal to noise at the output of the converter. The signal is the rms magnitude of the fundamental. Noise is the rms sum of all the nonfundamen- tal signals (excluding dc) up to half the sampling frequency. SNR is dependent on the number of quantization levels used in the digitization process; the more levels, the smaller the quanti- zation noise. The theoretical SNR for a sine wave is given by SNR = (6.02N + 1.76) dB where N is the number of bits. Thus for an ideal 8-bit converter, SNR = 50 dB. Harmonic Distortion Harmonic Distortion is the ratio of the rms sum of harmonics to the fundamental. For the AD7569/AD7669, Total Harmonic Distortion (THD) is defined as 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 individual harmonics. Intermodulation Distortion With inputs consisting of sine waves at two frequencies, fa and fb, any active device with nonlinearities will create distortion products, of order (m + n), at sum and difference frequencies of mfa ± nfb where m, n = 0, l, 2, 3,… . Intermodulation terms are those for which m or n is not equal to zero. For example, the second order terms include (fa + fb) and (fa – fb) and the third order terms include (2fa + fb), (2fa – fb), (fa + 2fb) and (fa – 2fb). |
Аналогичный номер детали - AD7569TQ2 |
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Аналогичное описание - AD7569TQ2 |
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