ADS6149_14 Datasheet, PDF (62/71 Pages) Texas Instruments – 14/12-Bit, 250/210 MSPS ADCs With DDR LVDS and Parallel CMOS Outputs

ADS6149/ADS6129
ADS6148/ADS6128
SLWS211B – JULY 2008 – REVISED OCTOBER 2008 ..................................................................................................................................................... www.ti.com
ENOB = ^{SINAD - 1.76}
6.02
(5)
Total Harmonic Distortion (THD) – THD is the ratio of the power of the fundamental (P_S) to the power of the
first nine harmonics (PD).
THD = 10Log^{10 PS}
P_N
(6)
THD is typically given in units of dBc (dB to carrier).
Spurious-Free Dynamic Range (SFDR) – The ratio of the power of the fundamental to the highest other
spectral component (either spur or harmonic). SFDR is typically given in units of dBc (dB to carrier).
Two-Tone Intermodulation Distortion – IMD3 is the ratio of the power of the fundamental (at frequencies f1
and f2) to the power of the worst spectral component at either frequency 2f1–f2 or 2f2–f1. IMD3 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.
DC Power Supply Rejection Ratio (DC PSRR) – The DC PSSR is the ratio of the change in offset error to a
change in analog supply voltage. The DC PSRR is typically given in units of mV/V.
AC Power Supply Rejection Ratio (AC PSRR) – AC PSRR is the measure of rejection of variations in the
supply voltage by the ADC. If ΔV_SUP is the change in supply voltage and ΔVout is the resultant change of the
ADC output code (referred to the input), then
PSRR = 20Log¹⁰
DV_OUT
DV_SUP
(Expressed in dBc)
(7)
Voltage Overload Recovery – The number of clock cycles taken to recover to less than 1% error after an
overload on the analog inputs. This is tested by separately applying a sine wave signal with 6dB positive and
negative overload. The deviation of the first few samples after the overload (from their expected values) is noted.
Common Mode Rejection Ratio (CMRR) – CMRR is the measure of rejection of variation in the analog input
common-mode by the ADC. If ΔVcm_in is the change in the common-mode voltage of the input pins and ΔV_OUT
is the resultant change of the ADC output code (referred to the input), then
CMRR = 20Log¹⁰
DV_OUT
DV_CM
(Expressed in dBc)
(8)
Cross-Talk (only for multi-channel ADC)– This is a measure of the internal coupling of a signal from adjacent
channel into the channel of interest. It is specified separately for coupling from the immediate neighboring
channel (near-channel) and for coupling from channel across the package (far-channel). It is usually measured
by applying a full-scale signal in the adjacent channel. Cross-talk is the ratio of the power of the coupling signal
(as measured at the output of the channel of interest) to the power of the signal applied at the adjacent channel
input. It is typically expressed in dBc.
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