11.1.1.1 Definition of Specifications

Analog Bandwidth
The analog input frequency at which the power of the fundamental is reduced by 3 dB with respect to the low-frequency value

Aperture Delay
The delay in time between the rising edge of the input sampling clock and the actual time at which the sampling occurs

Aperture Uncertainty (Jitter)
The sample-to-sample variation in aperture delay

Clock Pulse Duration/Duty Cycle
The duty cycle of a clock signal is the ratio of the time the clock signal remains at a logic high (clock pulse duration) to the period of the clock signal, expressed as a percentage.

Differential Nonlinearity (DNL)
An ideal ADC exhibits code transitions at analog input values spaced exactly 1 LSB apart. DNL is the deviation of any single step from this ideal value, measured in units of LSB.

Common-Mode Rejection Ratio (CMRR)
CMRR measures the ability to reject signals that are presented to both analog inputs simultaneously. The injected common-mode frequency level is translated into dBFS, the spur in the output FFT is measured in dBFS, and the difference is the CMRR in dB.

Effective Number of Bits (ENOB)
ENOB is a measure in units of bits of a converter's performance as compared to the theoretical limit based on quantization noise

Gain Error
Gain error is the deviation of the ADC actual input full-scale range from its ideal value, given as a percentage of the ideal input full-scale range.

Integral Nonlinearity (INL)
INL is the deviation of the ADC transfer function from a best-fit line determined by a least-squares curve fit of that transfer function. The INL at each analog input value is the difference between the actual transfer function and this best-fit line, measured in units of LSB.

Offset Error
Offset error is the deviation of output code from mid-code when both inputs are tied to common-mode.

Power-Supply Rejection Ratio (PSRR)
PSRR is a measure of the ability to reject frequencies present on the power supply. The injected frequency level is translated into dBFS, the spur in the output FFT is measured in dBFS, and the difference is the PSRR in dB. The measurement calibrates out the benefit of the board supply decoupling capacitors.

Signal-to-Noise Ratio (SNR)
SNR is the ratio of the power of the fundamental (P_S) to the noise floor power (P_N), excluding the power at dc and in the first five harmonics.

Equation 10.

SNR is either given in units of dBc (dB to carrier) when the absolute power of the fundamental is used as the reference, or dBFS (dB to full scale) when the power of the fundamental is extrapolated to the converter’s full-scale range.

Signal-to-Noise and Distortion (SINAD)
SINAD is the ratio of the power of the fundamental (P_S) to the power of all the other spectral components including noise (P_N) and distortion (P_D), but excluding dc.

Equation 11.

SINAD is either given in units of dBc (dB to carrier) when the absolute power of the fundamental is used as the reference, or dBFS (dB to full scale) when the power of the fundamental is extrapolated to the converter’s full-scale range.

Temperature Drift
Temperature drift (with respect to gain error and offset error) specifies the change from the value at the nominal temperature to the value at T_MIN or T_MAX. It is computed as the maximum variation the parameters over the whole temperature range divided by T_MIN – T_MAX.

Total Harmonic Distortion (THD)
THD is the ratio of the power of the fundamental (P_S) to the power of the first five harmonics (P_D).

Equation 12.

THD is typically given in units of dBc (dB to carrier).

Two-Tone Intermodulation Distortion (IMD3)
IMD3 is the ratio of the power of the fundamental (at frequencies f₁, f₂) to the power of the worst spectral component at either frequency 2f₁ – f₂ or 2f₂ – f₁). IMD3 is given in units of either dBc (dB to carrier) when the absolute power of the fundamental is used as the reference, or dBFS (dB to full scale) when the power of the fundamental is extrapolated to the converter’s full-scale range.