Datasheet AD7863 (Analog Devices) - 9

AD7863 TERMINOLOGY Signal-to-(Noise + Distortion) Ratio Channel-to-Channel Isolation
This is the measured ratio of signal to (noise + distortion) at the Channel-to-channel isolation is a measure of the level of output of the analog-to-digital converter. The signal is the rms crosstalk between channels. It is measured by applying a full- amplitude of the fundamental. Noise is the rms sum of all non- scale 50 kHz sine wave signal to all nonselected channels and fundamental signals up to half the sampling frequency (fS/2), determining how much that signal is attenuated in the selected excluding dc. The ratio is dependent upon the number of channel. The figure given is the worst case across all channels. quantization levels in the digitization process; the more levels, the smaller the quantization noise. The theoretical signal-to-
Relative Accuracy
(noise + distortion) ratio for an ideal N-bit converter with a sine Relative accuracy or endpoint nonlinearity is the maximum wave input is given by deviation from a straight line passing through the endpoints of the ADC transfer function. Signal to (Noise + Distortion) = (6.02N + 1.76) dB For a 14-bit converter, this is 86.04 dB.
Differential Nonlinearity
This is the difference between the measured and the ideal 1 LSB
Total Harmonic Distortion
change between any two adjacent codes in the ADC. Total harmonic distortion (THD) is the ratio of the rms sum of harmonics to the fundamental. For the AD7863 it is defined as
Positive Gain Error
(AD7863-10, ±10 V, AD7863-3, ±2.5 V) This is the deviation of the last code transition (01 . 110 to 2 2 2 2 + + + 01 . 111) from the ideal 4 × VREF − 1 LSB (AD7863-10, ±10 V THD (dB) V V V V 2 3 4 5 = 20 log V range) or VREF − 1 LSB (AD7863-3, ±2.5 V range), after the 1 bipolar offset error has been adjusted out. where: V
Positive Gain Error
(AD7863-2, 0 V to 2.5 V) 1 is the rms amplitude of the fundamental. V This is the deviation of the last code transition (11 . 110 to 2, V3, V4, and V5 are the rms amplitudes of the second through the fifth harmonics. 11 . 111) from the ideal VREF − 1 LSB, after the unipolar offset error has been adjusted out.
Peak Harmonic or Spurious Noise
Peak harmonic or spurious noise is defined as the ratio of the
Bipolar Zero Error
(AD7863-10, ±10 V, AD7863-3, ±2.5 V) rms value of the next largest component in the ADC output This is the deviation of the midscale transition (all 0s to all 1s) spectrum (up to f from the ideal 0 V (AGND). S/2 and excluding dc) to the rms value of the fundamental. Normally, the value of this specification is
Unipolar Offset Error
(AD7863-2, 0 V to 2.5 V) determined by the largest harmonic in the spectrum, but for This is the deviation of the first code transition (00 . 000 to parts where the harmonics are buried in the noise floor, it is 00 . 001) from the ideal AGND + 1 LSB. a noise peak.
Negative Gain Error
(AD7863-10, ±10 V, AD7863-3, ±2.5 V)
Intermodulation Distortion
This is the deviation of the first code transition (10 . 000 to With inputs consisting of sine waves at two frequencies, fa and 10 . 001) from the ideal −4 × VREF + 1 LSB (AD7863-10, ±10 V fb, any active device with nonlinearities creates distortion range) or –VREF + 1 LSB (AD7863-3, ±2.5 V range), after bipolar products at sum and difference frequencies of mfa ± nfb where zero error has been adjusted out. m, n = 0, 1, 2, 3. Intermodulation terms are those for which neither m nor n is equal to zero. For example, the second order
Track-and-Hold Acquisition Time
terms include (fa + fb) and (fa − fb), and the third order terms Track-and-hold acquisition time is the time required for the include (2fa + fb), (2fa − fb), (fa + 2fb), and (fa − 2fb). output of the track/hold amplifier to reach its final value, with The AD7863 is tested using two input frequencies. In this case, ±½ LSB, after the end of conversion (the point at which the the second and third order terms are of different significance. track-and-hold returns to track mode). It also applies to The second order terms are usually distanced in frequency from situations where a change in the selected input channel takes the original sine waves, and the third order terms are usually at place or where there is a step input change on the input voltage a frequency close to the input frequencies. As a result, the applied to the selected VAX/BX input of the AD7863. It means second and third order terms are specified separately. The that the user must wait for the duration of the track-and-hold calculation of the intermodulation distortion is as per the THD acquisition time after the end of conversion or after a channel specification where it is the ratio of the rms sum of the change/step input change to VAX/BX before starting another individual distortion products to the rms amplitude of the conversion, to ensure that the part operates to specification. fundamental, expressed in decibels (dB). Rev. B | Page 8 of 24 Document Outline FEATURES GENERAL DESCRIPTION PRODUCT HIGHLIGHTS TABLE OF CONTENTS REVISION HISTORY SPECIFICATIONS TIMING CHARACTERISTICS ABSOLUTE MAXIMUM RATINGS ESD CAUTION PIN CONFIGURATION AND FUNCTION DESCRIPTIONS TERMINOLOGY CONVERTER DETAILS TRACK-AND-HOLD SECTION REFERENCE SECTION CIRCUIT DESCRIPTION ANALOG INPUT SECTION OFFSET AND FULL-SCALE ADJUSTMENT Positive Full-Scale Adjust (−10 Version) Negative Full-Scale Adjust (−10 Version) TIMING AND CONTROL Read Options OPERATING MODES MODE 1 OPERATION Normal Power, High Sampling Performance MODE 2 OPERATION Power-Down, Auto-Sleep After Conversion AD7863 DYNAMIC SPECIFICATIONS SIGNAL-TO-NOISE RATIO (SNR) EFFECTIVE NUMBER OF BITS TOTAL HARMONIC DISTORTION (THD) INTERMODULATION DISTORTION PEAK HARMONIC OR SPURIOUS NOISE DC LINEARITY PLOT POWER CONSIDERATIONS MICROPROCESSOR INTERFACING AD7863 TO ADSP-2100 INTERFACE AD7863 TO ADSP-2101/ADSP-2102 INTERFACE AD7863 TO TMS32010 INTERFACE AD7863 TO TMS320C25 INTERFACE AD7863 TO MC68000 INTERFACE AD7863 TO 80C196 INTERFACE VECTOR MOTOR CONTROL MULTIPLE AD7863S APPLICATIONS HINTS PC BOARD LAYOUT CONSIDERATIONS GROUND PLANES POWER PLANES SUPPLY DECOUPLING OUTLINE DIMENSIONS ORDERING GUIDE