ADS5474 Datasheet, PDF (31/38 Pages) Texas Instruments – 14-Bit, 400-MSPS Analog-to-Digital Converter

ADS5474
www.ti.com
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 converter
performance as compared to the theoretical limit
based on quantization noise:
ENOB = (SINAD – 1.76)/6.02
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.
SLAS525 – JULY 2007
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
(4)
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 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
(5)
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 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).
THD
+
10log₁₀
P_S
P_D
(6)
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 full-scale range.
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