ADS6445 Datasheet, PDF (68/75 Pages) STMicroelectronics – QUAD CHANNEL, 14-BIT, 125/105/80/65 MSPS ADC WITH SERIAL LVDS OUTPUTS

ADS6445, ADS6444
ADS6443, ADS6442
SLAS531 – MAY 2007
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. 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 – The 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. The gain error does not include the error
caused by the internal reference deviation from ideal value. This is specifed separately as internal reference
error. The maximum variation of the gain error across devices and across channels within a device is specified
separately.
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
+
10Log10
P_S
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
+
10Log10
P_S
PN ) PD
(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 a converter’s performance as compared to the
theoretical limit based on quantization noise.
ENOB
+
SINAD *
6.02
1.76
(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).
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