ADS5400 Datasheet, PDF (46/55 Pages) Texas Instruments – 12-Bit, 1-GSPS Analog-to-Digital Converter

ADS5400
SLAS611C – OCTOBER 2009 – REVISED JANUARY 2016
11 Device and Documentation Support
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11.1 Device Support
11.1.1 Device Nomenclature
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
ENOB = (SINAD – 1.76)/ 6.02
(7)
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
SNR
=
10Log₁₀
P_S
P_N
(8)
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.
SINAD
=
10Log₁₀
P_S
P_N + P_D
(9)
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.
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