Datasheet AD7992 (Analog Devices) - 10

AD7992 TERMINOLOGY Signal-to-Noise and Distortion Ratio (SINAD) Channel-to-Channel Isolation
The measured ratio of signal-to-noise and distortion at the A measure of the level of crosstalk between channels, taken output of the A/D converter. The signal is the rms amplitude of by applying a full-scale sine wave signal to the unselected input the fundamental. Noise is the sum of all nonfundamental signals channels, and determining how much the 108 Hz signal is up to half the sampling frequency (fS/2), excluding dc. The ratio attenuated in the selected channel. The sine wave signal applied is dependent on the number of quantization levels in the digit- to the unselected channels is then varied from 1 kHz up to ization process; the more levels, the smaller the quantization 2 MHz, each time determining how much the 108 Hz signal in noise. The theoretical signal-to-noise and distortion ratio for the selected channel is attenuated. This figure represents the an ideal N-bit converter with a sine wave input is given by worst-case level across all channels. Signal-to-(Noise + Distortion) = (6.02 N + 1.76) dB
Aperture Delay
Thus, the SINAD is 74 dB for a 12-bit converter. The measured interval between the sampling clock’s leading edge and the point at which the ADC takes the sample.
Total Harmonic Distortion (THD)
The ratio of the rms sum of harmonics to the fundamental. For
Aperture Jitter
the AD7992, it is defined as The sample-to-sample variation in the effective point in time when the sample is taken. 2 2 2 2 2 V + V + V + V + V 2 3 4 5 6 THD ( ) dB = 20 log
Full-Power Bandwidth
V1 The input frequency at which the amplitude of the reconstructed fundamental is reduced by 0.1 dB or 3 dB for a full-scale input. where V1 is the rms amplitude of the fundamental, and V2, V3, V4, V5, and V6 are the rms amplitudes of the second through
Power Supply Rejection Ratio (PSRR)
sixth harmonics. The ratio of the power in the ADC output at the full-scale frequency, f, to the power of a 200 mV p-p sine wave applied
Peak Harmonic or Spurious Noise
to the ADC VDD supply of frequency fS: The ratio of the rms value of the next largest component in the ADC output spectrum (up to f PSRR (dB) = 10 log (Pf/Pf S/2 and excluding dc) to the rms S) value of the fundamental. Typically, the value of this specification where Pf is the power at frequency f in the ADC output; PfS is is determined by the largest harmonic in the spectrum, but for the power at frequency fS coupled onto the ADC VDD supply. ADCs where the harmonics are buried in the noise floor, it is a noise peak.
Integral Nonlinearity
The maximum deviation from a straight line passing through
Intermodulation Distortion
the endpoints of the ADC transfer function. The endpoints are With inputs consisting of sine waves at two frequencies, fa zero scale, a point 1 LSB below the first code transition, and full and fb, any active device with nonlinearities creates distortion scale, a point 1 LSB above the last code transition. products at sum and difference frequencies of mfa ± nfb, where m, n = 0, 1, 2, 3, and so on. Intermodulation distortion terms
Differential Nonlinearity
are those for which neither m nor n equal zero. For example, The difference between the measured and the ideal 1 LSB second-order terms include (fa + fb) and (fa − fb), while change between any two adjacent codes in the ADC. third-order terms include (2fa + fb), (2fa − fb),(fa + 2fb), and (fa − 2fb).
Offset Error
The deviation of the first code transition (00…000) to The AD7992 is tested using the CCIF standard where two input (00…001) from the ideal—that is, AGND + 1 LSB. frequencies near the top end of the input bandwidth are used. In this case, the second-order terms are usually distanced in
Offset Error Match
frequency from the original sine waves while the third-order The difference in offset error between any two channels. terms are usually at a frequency close to the input frequencies.
Gain Error
As a result, the second- and third-order terms are specified The deviation of the last code transition (111…110) to separately. The calculation of intermodulation distortion is, (111…111) from the ideal (that is, REFIN − 1 LSB) after the like the THD specification, the ratio of the rms sum of the offset error has been adjusted out. individual distortion products to the rms amplitude of the sum of the fundamentals, expressed in dB.
Gain Error Match
The difference in gain error between any two channels. Rev. 0 | Page 9 of 28 Document Outline FEATURES GENERAL DESCRIPTION FUNCTIONAL BLOCK DIAGRAM PRODUCT HIGHLIGHTS SPECIFICATIONS I2C TIMING SPECIFICATIONS ABSOLUTE MAXIMUM RATINGS ESD CAUTION PIN CONFIGURATION AND PIN FUNCTION DESCRIPTIONS TERMINOLOGY TYPICAL PERFORMANCE CHARACTERISTICS CIRCUIT INFORMATION CONVERTER OPERATION TYPICAL CONNECTION DIAGRAM ANALOG INPUT INTERNAL REGISTER STRUCTURE ADDRESS POINTER REGISTER CONFIGURATION REGISTER CONVERSION RESULT REGISTER LIMIT REGISTERS ALERT STATUS REGISTER CYCLE TIMER REGISTER SAMPLE DELAY AND BIT TRIAL DELAY SERIAL INTERFACE SERIAL BUS ADDRESS WRITING TO THE AD7992 WRITING TO THE ADDRESS POINTER REGISTER FOR A SUBSEQUENT REA WRITING A SINGLE BYTE OF DATA TO THE ALERT STATUS REGISTER, WRITING TWO BYTES OF DATA TO A LIMITREGISTER OR HYSTERESIS READING DATA FROM THE AD7992 ALERT/BUSY PIN SMBus ALERT PLACING THE AD7992-1 INTO HIGH SPEED MODE THE ADDRESS SELECT (AS) PIN MODES OF OPERATION MODE 1—USING THE /CONVST PIN MODE 2 – COMMAND MODE MODE 3—AUTOMATIC CYCLE MODE OUTLINE DIMENSIONS ORDERING GUIDE