Datasheet AD7760 (Analog Devices) - 12

AD7760 TERMINOLOGY
Signal-to-Noise Ratio (SNR) Integral Nonlinearity (INL)
SNR is the ratio of the rms value of the actual input signal to the INL is the maximum deviation from a straight line passing rms sum of all other spectral components below the Nyquist through the endpoints of the ADC transfer function. frequency, excluding harmonics and dc. The value for SNR is expressed in decibels.
Differential Nonlinearity (DNL)
DNL is the difference between the measured and the ideal
Total Harmonic Distortion (THD)
1 LSB change between any two adjacent codes in the ADC. THD is the ratio of the rms sum of harmonics to the fundamental. For the AD7760, it is defined as
Zero Error
Zero error is the difference between the ideal midscale input 2 2 2 2 2 voltage (when both inputs are shorted together) and the actual THD dB V V V V V 2 3 4 5 6 20 log voltage producing the midscale output code. V1 where:
Zero Error Drift
V Zero error drift is the change in the actual zero error value due 1 is the rms amplitude of the fundamental. V to a temperature change of 1°C. It is expressed as a percentage 2, V3, V4, V5, and V6 are the rms amplitudes of the second to the sixth harmonics. of full scale at room temperature.
Nonharmonic Spurious-Free Dynamic Range (SFDR) Gain Error
SFDR is the ratio of the rms signal amplitude to the rms value The first transition (from 100 … 000 to 100 … 001) should of the peak spurious spectral component, excluding harmonics. occur for an analog voltage ½ LSB above the nominal negative full scale. The last transition (from 011 … 110 to 011 … 111)
Dynamic Range
should occur for an analog voltage 1½ LSB below the nominal Dynamic range is the ratio of the rms value of the full scale to full scale. The gain error is the deviation of the difference the rms noise measured with the inputs shorted together. The between the actual level of the last transition and the actual value for the dynamic range is expressed in decibels. level of the first transition, from the difference between the ideal levels.
Intermodulation Distortion
With inputs consisting of sine waves at two frequencies, fa and
Gain Error Drift
fb, any active device with nonlinearities creates distortion products Gain error drift is the change in the actual gain error value due at sum and difference frequencies of mfa ± nfb, where m, n = 0, to a temperature change of 1°C. It is expressed as a percentage 1, 2, 3, and so on. Intermodulation distortion terms are those of full scale at room temperature. for which neither m nor n are equal to 0. 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). The AD7760 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, and 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 decibels. Rev. A | Page 11 of 36