ADS6149_1 Datasheet, PDF (61/69 Pages) Texas Instruments – 14/12-Bit, 250/210 MSPS ADCs With DDR LVDS and Parallel CMOS Outputs

ADS6149/ADS6129
ADS6148/ADS6128
www.ti.com ..................................................................................................................................................... SLWS211B – JULY 2008 – REVISED OCTOBER 2008
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. This delay will be different across channels. The maximum variation is specified as
aperture delay variation (channel-channel).
Aperture Uncertainty (Jitter) – The sample-to-sample variation in aperture delay.
Clock Pulse Width/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 width) to the period of the clock signal. Duty cycle is typically expressed as a
percentage. A perfect differential sine-wave clock results in a 50% duty cycle.
Maximum Conversion Rate – The maximum sampling rate at which certified operation is given. All parametric
testing is performed at this sampling rate unless otherwise noted.
Minimum Conversion Rate – The minimum sampling rate at which the ADC functions.
Differential Nonlinearity (DNL) – An ideal ADC exhibits code transitions at analog input values spaced exactly
1 LSB apart. The DNL is the deviation of any single step from this ideal value, measured in units of LSBs.
Integral Nonlinearity (INL) – The INL is the deviation of the ADC's transfer function from a best fit line
determined by a least squares curve fit of that transfer function, measured in units of LSBs.
Gain Error – Gain error is the deviation of the ADC's actual input full-scale range from its ideal value. The gain
error is given as a percentage of the ideal input full-scale range. Gain error has two components: error due to
reference inaccuracy and error due to the channel. Both these errors are specified independently as E_GREF and
E_GCHAN.
To a first order approximation, the total gain error will be E_TOTAL ~ E_GREF + E_GCHAN.
For example, if E_TOTAL = ±0.5%, the full-scale input varies from (1-0.5/100) x FS_ideal to (1 + 0.5/100) x FS_ideal.
Offset Error – The offset error is the difference, given in number of LSBs, between the ADC's actual average
idle channel output code and the ideal average idle channel output code. This quantity is often mapped into mV.
Temperature Drift – The temperature drift coefficient (with respect to gain error and offset error) specifies the
change per degree Celsius of the parameter from T_MIN to T_MAX. It is calculated by dividing the maximum deviation
of the parameter across the T_MIN to T_MAX range by the difference T_MAX–T_MIN.
Signal-to-Noise Ratio – SNR is the ratio of the power of the fundamental (PS) to the noise floor power (PN),
excluding the power at DC and the first nine harmonics.
SNR = 10Log^{10 PS}
P_N
(3)
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 = 10Log^{10 PS}
P_N + P_D
(4)
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.
Effective Number of Bits (ENOB) – The ENOB is a measure of the converter performance as compared to the
theoretical limit based on quantization noise.
Copyright © 2008, Texas Instruments Incorporated
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Product Folder Link(s): ADS6149/ADS6129 ADS6148/ADS6128